Physical Geology
Unit 1
Introduction: Definition, Aim and Scope of geology, relationship with other branches of science, branches of Geology.
INTRODUCTION TO GEOLOGY
Geology (in Greek, Geo means Earth, Logos means Science) is a branch of science dealing with the
study of the Earth. It is also known as earth science. The study of the earth comprises of the whole
earth, its origin, structure, composition and history (including the development of life) and the nature of
the processes. The word was first used in 1778 in the work of Jean Andrea de Luc (a Swiss-born
scientist who lived at Windsor for much of his life as adviser to Queen Charlotte) and at much the same
time in the work of Swiss Chemist, S.B. Saucer.
Geology is a fascinating subject.
Geology feels the pulse of the earth.
Geologists contribute their part to the nation through the discovery of new deposits of rocks and
minerals of economic value.
A student should know what lies beneath the crust and how long back the earth came into existence.
DIFFERENT BRANCHES OF GEOLOGY
For studying the earth in detail, the subject of Geology has been divided into various branches as
follows:
(i) Physical Geology
(ii) Crystallography
(iii) Mineralogy
(iv) Petrology
(v) Structural Geology
(vi) Stratigraphy
(vii) Paleontology
(viii) Historical Geology
(ix) Economic Geology
(x) Mining Geology
(xi) Civil Engineering Geology
(xii) Hydrology
(xiii) Indian Geology
(xiv) Resources Engineering
(xv) Photo Geology
(i) Physical Geology
As a branch of geology, it deals with the “various processes of physical agents such as wind, water,
glaciers and sea waves”, run on these agents go on modifying the surface of the earth continuously.
Physical geology includes the study of Erosion, Transportation and Deposition (ETD).
The study of physical geology plays a vital role in civil engineering thus:
(a) It reveals constructive and destructive processes of physical agents at a particular site.
(b) It helps in selecting a suitable site for different types of project to be under taken after studying
the effects of physical agents which go on modifying the surface of the earth physically,
chemically and mechanically.
(ii) Crystallography
As a branch of geology, it deals with ‘the study of crystals’. A crystal is a regular polyhedral form
bounded by smooth surfaces.
The study of crystallography is not much important to civil engineering, but to recognize the minerals
the study of crystallography is necessary.
(iii) Mineralogy
As a branch of geology, it deals with ‘the study of minerals’. A mineral may be defined as a naturally
occurring, homogeneous solid, inorganically formed, having a definite chemical composition and ordered
atomic arrangement. The study of mineralogy is most important.
(a) For a civil engineering student to identify the rocks.
(b) In industries such as cement, iron and steel, fertilizers, glass industry and so on.
(c) In the production of atomic energy.
(iv) Petrology
As a branch of geology it deals with ‘the study of rocks’. A rock is defined as “the aggregation of
minerals found in the earth’s crust”.
The study of petrology is most important for a civil engineer, in the selection of suitable rocks for
building stones, road metals, etc.
(v) Structural Geology
As a branch of geology, it deals with ‘the study of structures found in rocks’. It is also known as
tectonic geology or simply tectonics.
Structural geology is an arrangement of rocks and plays an important role in civil engineering in the
selection of suitable sites for all types of projects such as dams, tunnels, multistoried buildings, etc.
(vi) Stratigraphy
As a branch of geology it deals with ‘the study of stratified rocks and their correlation’.
(vii) Paleontology
As a branch of geology, it deals with ‘the study of fossils’ and the ancient remains of plants and animals
are referred to as fossils. Fossils are useful in the study of evolution and migration of animals and plants
through ages, ancient geography and climate of an area.Introduction and Scope 3
(viii) Historical Geology
As a branch of geology, it includes “the study of both stratigraphy and paleontology”. Its use in civil
engineering is to know about the land and seas, the climate and the life of early times upon the earth.
(ix) Economic Geology
As a branch of Geology, it deals with “the study of minerals, rocks and materials of economic importance
like coal and petroleum”.
(x) Mining Geology
As a branch of geology, it deals with “the study of application of geology to mining engineering in such
a way that the selection of suitable sites for quarrying and mines can be determined”.
(xi) Civil Engineering Geology
As a branch of geology, it deals with “all the geological problems that arise in the field of civil engineering
along with suitable treatments”. Thus, it includes the construction of dams, tunnels, mountain roads,
building stones and road metals.
(xii) Hydrology
As a branch of geology, it deals with “the studies of both quality and quantity of water that are present
in the rocks in different states”(Conditions). Moreover, it includes:
(a) Atmospheric water,
(b) Surface water, and
(c) Underground water.
(xiii) Indian Geology
As a branch of geology, it deals with “the study of our motherland in connection with the coal/petroleum,
physoigraphy, stratigraphy and economic mineral of India”.
(xiv) Resources Engineering
As a branch of geology deals with “the study of water, land, solar energy, minerals, forests, etc. fulfill
the human wants”.
(xv) Photo Geology
As a branch of geology deals with “the study of aerial photographs”.
RELATIONSHIP OF GEOLOGY WITH OTHER BRANCHES OF SCIENCE
AND ENGINEERING
In order to carry out civil engineering projects safely and successfully, geology should be related to the
other branches of bordering sciences as described as follows:4 A Textbook of Applied Engineering Geology
1. Geochemistry
As a branch of science, it deals with geology in such a way that it concerns with the abundance and
distribution of various elements and compounds in the earth.
2. Geophysics
As a branch of science, it is related with geology in such a way that it concerns with the constitution of
the earth and the nature of the physical forces operating on with in the earth.
3. Geohydrology
As a branch of science, it is related with geology in setting of ground water. In other words, Geohydrology
is an “interaction between Geology and Hydrology”.
4. Rock Mechanics
As a branch of science, it is related with geology in dealing with the behaviour of rocks that is subjected
to static and dynamic loads (force fields).
5. Mining Engineering
Geology is related to mining engineering in dealing with the formation and distribution of economic
minerals and response to fracturing processes. With out the knowledge of structural features of rock
masses and mode of occurrence and mineral deposits, a mining engineer cannot determine the method
of mining.
6. Civil Engineering
Before constructing roads, bridges, tunnels, tanks, reservoirs and buildings, selection of site is important
from the viewpoint of stability of foundation and availability of construction materials. Geology of area
is important and rock-forming region, their physical nature, permeability, faults, joints, etc. Thus, geology
is related to civil engineering in construction jobs with economy and success.
IMPORTANCE OF GEOLOGY FOR CIVIL ENGINEERING
The role of geology in civil engineering may be briefly outlined as follows:
1. Geology provides a systematic knowledge of construction materials, their structure and
properties.
2. The knowledge of Erosion, Transportation and Deposition (ETD) by surface water helps in
soil conservation, river control, coastal and harbour works.
3. The knowledge about the nature of the rocks is very necessary in tunneling, constructing
roads and in determining the stability of cuts and slopes. Thus, geology helps in civil engineering.
4. The foundation problems of dams, bridges and buildings are directly related with geology of
the area where they are to be built.
5. The knowledge of ground water is necessary in connection with excavation works, water
supply, irrigation and many other purposes.
6. Geological maps and sections help considerably in planning many engineering projects.Introduction and Scope 5
7. If the geological features like faults, joints, beds, folds, solution channels are found, they have
to be suitably treated. Hence, the stability of the structure is greatly increased.
8. Pre-geological survey of the area concerned reduces the cost of engineering work.
SCOPE OF GEOLOGY
Engineering Geology: A well established interdisciplinary branch of Science and Engineering has a
scope in different fields as outlined below:
(a) In Civil Engineering: Geology provides necessary information about the site of construction
materials used in the construction of buildings, dams, tunnels, tanks, reservoirs, highways
and bridges. Geological information is most important in planning phase (stage), design phase
and construction phase of an engineering project.
(b) In Mining Engineering: Geology is useful to know the method of mining of rock and mineral
deposits on earth’s surface and subsurface.
(c) In Ground Water: Resources development geology is applied in various aspects of resources
and supply, storage, filling up of reservoirs, pollution disposal and contaminated water disposal.
(d) Land pollution.
(e) Nuclear explosion.
(f) Oceanography.
(g) Space exploration.
In each of the above-mentioned fields Geology has to deal with an integral part of the earth.
EARTH AS A PLANET
The earth is a planet belonging to the solar system of the Milky Way Galaxy, with a natural satellite, the
moon. It is the third planet from the Sun. The planet on which we live is called the earth. There is a lot
of disagreement between the scientists regarding the shape of the earth. In recent times a new phrase
being used is that the earth is like a GEOID (Greek, GEO = earth, OID = like) i.e., our planet is like the
earth. They believe that the interior of the earth is shrinking day by day. This shrinkage may be either due
to loss of heat or reorganization of molecules under enormous pressure and high temperature. It is thus
obvious that the outer portion must shorten its circumference to adjust the shrunken interior.
Chart of the diameter and the area of the earth, according to the present state of
knowledge about it
STRUCTURES AND COMPOSITION OF EARTH
The outer envelopes of the gaseous material surrounding the earth are called atmosphere. Under the
atmosphere is our earth on which we live. That part of the earth, which is in the form of a land, is
known as the earth’s crust. It also includes the highest peaks of mountains and floors of the oceans.
Part of the land, which is visible on the Globe, is called the Lithosphere (Greek, Litho = Stone).
We know that nearly 75 per cent of the whole surface of the earth is covered with natural waters
like oceans, seas, lakes, rivers etc. Which is in the form of more or less, a continuous envelope around
the earth. This envelope of water is called Hydrosphere (Greek, Hudous = Water). Thus, Lithosphere
and Hydrosphere in a combined form is known as the Earth’s crust. Under the Earth’s crust is the
interior of the Earth. It is further sub-divided into three shells. Depending upon the nature, the material
is made up as shown in the Fig. 1.1.
The earth is composed of different rocks. In an ordinary sense the term rock means something hard
and resistant but the meaning of the word has been extended so as to include all natural substances of
the Earth’s crust, which may be hard like granite or soft like clay and sand. It has been estimated that
95 per cent of the Earth’s crust is made up of primary i.e., first formed (Igneous) rocks which is mostly
composed of Granite having Quartz, Feldspar, Biotite mica and Hornblende in varying proportions the remaining 5 per cent of the crust is made up of Secondary (Sedimentary or Metamorphic) rocks (as shown in Fig. 1.2). The Earth’s crust is in the form of a very thin layer of solidified rocks and is
heterogeneous in nature. These rocks may be classified on the basis of their density into the following
two groups:
1. Sial (Si = Silicon and Al = Aluminium) having density 2.75 to 2.90.
2. Sima (Si = Silicon and Ma= Magnesium) having density 2.90 to 4.75.
It has been estimated that the Sial rocks are about 70 per cent of the Earth’s crust, which include
chiefly Granite and Silica. These rocks are generally on the upper regions of the crust.
Sima rocks include heavy and dark coloured rocks like Basalts. In these rocks, the percentage of
Silica is reduced and Magnesium attains the next importance in place of Aluminium of Sial rocks. These
rocks are generally found on the floors of the Oceans and beneath sial rocks.
Mantle: It is the part of the earth below the crust and surrounding the core. The imaginary line that
separates the lithosphere from the mantle is known as ‘Moho’ (Mohorovicic discontinuity). Because of
high temperature and great pressure, the mineral matter in this part is the molten condition.
Core: It is the innermost layer of the earth; it extends from below the mantle (Gutenberg discontinuity)
to the central part of the earth. On the basis of earthquake waves, the core has been further divided into
two cores.
(a) Outer core
(b) Inner core
The outer core is 2,250 km thick and surrounds the core. It is believed that it is still in molten
condition.
The inner core is also called ‘Nife’ because it consists of Nickel and iron. Its thickness is about
1,228 km. It is very hard in nature.
Table 1.2 Thickness and composition of different layers of the earth
SOLAR SYSTEM
What Is The Solar System?
The Solar System is made up of all the planets that orbit our Sun. In addition to planets, the Solar System also consists of moons, comets, asteroids, minor planets, and dust and gas.
Everything in the Solar System orbits or revolves around the Sun. The Sun contains around 98% of all the material in the Solar System. The larger an object is, the more gravity it has. Because the Sun is so large, its powerful gravity attracts all the other objects in the Solar System towards it. At the same time, these objects, which are moving very rapidly, try to fly away from the Sun, outward into the emptiness of outer space. The result of the planets trying to fly away, at the same time that the Sun is trying to pull them inward is that they become trapped half-way in between. Balanced between flying towards the Sun, and escaping into space, they spend eternity orbiting around their parent star.
Our solar system is filled with a wide assortment of celestial bodies - the Sun itself, our eight planets, dwarf planets, and asteroids - and on Earth, life itself! The inner solar system is occasionally visited by comets that loop in from the outer reaches of the solar system on highly elliptical orbits. In the outer reaches of the solar system, we find the Kuiper Belt and the Oort cloud. Still farther out, we eventually reach the limits of the heliosphere, where the outer reaches of the solar system interact with interstellar space. Solar system formation began billions of years ago, when gases and dust began to come together to form the Sun, planets, and other bodies of the solar system.
Planet Earth: Forms and Dimensions of the Earth and its position in solar system.
From the perspective we get on Earth, our planet appears to be big and sturdy with an endless ocean of air. From space, astronauts often get the impression that the Earth is small with a thin, fragile layer of atmosphere. For a space traveler, the distinguishing Earth features are the blue waters, brown and green land masses and white clouds set against a black background.
Many dream of traveling in space and viewing the wonders of the universe. In reality all of us are space travelers. Our spaceship is the planet Earth, traveling at the speed of 108,000 kilometers (67,000 miles) an hour.
Earth is the 3rd planet from the Sun at a distance of about 150 million kilometers (93.2 million miles). It takes 365.256 days for the Earth to travel around the Sun and 23.9345 hours for the Earth rotate a complete revolution. It has a diameter of 12,756 kilometers (7,973 miles), only a few hundred kilometers larger than that of Venus. Our atmosphere is composed of 78 percent nitrogen, 21 percent oxygen and 1 percent other constituents.
Earth is the only planet in the solar system known to harbor life. Our planet's rapid spin and molten nickel-iron core give rise to an extensive magnetic field, which, along with the atmosphere, shields us from nearly all of the harmful radiation coming from the Sun and other stars. Earth's atmosphere protects us from meteors, most of which burn up before they can strike the surface.
From our journeys into space, we have learned much about our home planet. The first American satellite, Explorer 1, discovered an intense radiation zone, now called the Van Allen radiation belts. This layer is formed from rapidly moving charged particles that are trapped by the Earth's magnetic field in a doughnut-shaped region surrounding the equator. Other findings from satellites show that our planet's magnetic field is distorted into a tear-drop shape by the solar wind. We also now know that our wispy upper atmosphere, once believed calm and uneventful, seethes with activity -- swelling by day and contracting by night. Affected by changes in solar activity, the upper atmosphere contributes to weather and climate on Earth.
Besides affecting Earth's weather, solar activity gives rise to a dramatic visual phenomenon in our atmosphere. When charged particles from the solar wind become trapped in Earth's magnetic field, they collide with air molecules above our planet's magnetic poles. These air molecules then begin to glow and are known as the
auroras or the
northern and southern lights.
Terrestrial planet
The Terrestrial Planets are small and solid (like the Earth) and are made of rock and metal. The are also called the Inner Planets because they are fairly close to the Sun. They have no or very few satellites. In order from the Sun, these planets are Mercury, Venus, Earth and Mars.
Terrestrial planets are Earth-like planets (in Latin, terra means Earth) made up of rocks or metals with a hard surface — making them different from other planets that lack a solid surface. Terrestrial planets also have a molten heavy metal core, few moons, and a variety of topological features like valleys, volcanoes and craters. In our solar system, there are four terrestrial planets, which also happen to be the four closest to the sun: Mercury, Venus Earth and Mars. During the creation of the solar system, there were likely more terrestrial planetoids, but they likely merged or were destroyed.
 |
| The terrestrial planets or our solar system: Mercury, Venus, Earth & Mars |
MERCURY
Mercury is the closest planet to the Sun and due to its proximity it is not easily seen except during twilight. For every two orbits of the Sun, Mercury completes three rotations about its axis and up until 1965 it was thought that the same side of Mercury constantly faced the Sun. Thirteen times a century Mercury can be observed from the Earth passing across the face of the Sun in an event called a transit, the next will occur on the 9th May 2016.
Planet Profile
Mass: 330,104,000,000,000 billion kg (0.055 x Earth)
Equatorial Diameter: 4,879
Polar Diameter: 4,879
Equatorial Circumference: 15,329 km
Known Moons: none
Notable Moons: none
Orbit Distance: 57,909,227 km (0.39 AU)
Orbit Period: 87.97 Earth days
Surface Temperature: -173 to 427°C
First Record: 14th century BC
Recorded By: Assyrian astronomers
Size Of Mercury Compared To The Earth
Facts About Mercury
A year in Mercury is just 88 days long:
One day on Mercury lasts the equivalent of 176 Earth days. Mercury is nearly tidally locked to the Sun and over time this has slowed the rotation of the planet to almost match its orbit around the Sun. Mercury also has the highest orbital eccentricity of all the planets with its distance from the Sun ranging from 46 to 70 million km
Mercury is the smallest planet in the Solar System:
One of five planets visible with the naked eye a, Mercury is just 4,879 Kilometres across its equator, compared with 12,742 Kilometres for the Earth.
Mercury is the second densest planet:
Even though the planet is small, Mercury is very dense. Each cubic centimetre has a density of 5.4 grams, with only the Earth having a higher density. This is largely due to Mercury being composed mainly of heavy metals and rock.
Mercury has wrinkles:
As the iron core of the planet cooled and contracted, the surface of the planet became wrinkled. Scientist have named these wrinkles, Lobate Scarps. These Scarps can be up to a mile high and hundreds of miles long.
Mercury has a molten core:
In recent years scientists from NASA have come to believe the solid iron core of Mercury could in fact be molten. Normally the core of smaller planets cools rapidly, but after extensive research, the results were not in line with those expected from a solid core. Scientists now believe the core to contain a lighter element such as sulphur, which would lower the melting temperature of the core material. It is estimated Mercury’s core makes up 42% of its volume, while the Earth’s core makes up 17%.
Mercury is only the second hottest planet:
Despite being further from the Sun, Venus experiences higher temperatures. The surface of Mercury which faces the Sun sees temperatures of up to 427°C, whilst on the alternate side this can be as low as -173°C. This is due to the planet having no atmosphere to help regulate the temperature.
Mercury is the most cratered planet in the Solar System:
Unlike many other planets which “self-heal” through natural geological processes, the surface of Mercury is covered in craters. These are caused by numerous encounters with asteroids and comets. Most Mercurian craters are named after famous writers and artists. Any crater larger than 250 kilometres in diameter is referred to as a Basin. The Caloris Basin is the largest impact crater on Mercury covering approximately 1,550 km in diameter and was discovered in 1974 by the Mariner 10 probe.
Only two spacecraft have ever visited Mercury:
Owing to its proximity to the Sun, Mercury is a difficult planet to visit. During 1974 and 1975 Mariner 10 flew by Mercury three times, during this time they mapped just under half of the planet’s surface. On August 3rd 2004, the Messenger probe was launched from Cape Canaveral Air Force Station, this was the first spacecraft to visit since the mid 1970’s.
Mercury is named for the Roman messenger to the gods:
The exact date of Mercury’s discovery is unknown as it pre-dates its first historical mention, one of the first mentions being by the Sumerians around in 3,000 BC.
Mercury has an atmosphere (sort of):
Mercury has just 38% the gravity of Earth, this is too little to hold on to what atmosphere it has which is blown away by solar winds. However while gases escape into space they are constantly being replenished at the same time by the same solar winds, radioactive decay and dust caused by micrometeorites
VENUS
Venus is the second planet from the Sun and is the second brightest object in the night sky after the Moon. Named after the Roman goddess of love and beauty, Venus is the second largest terrestrial planet and is sometimes referred to as the Earth’s sister planet due the their similar size and mass. The surface of the planet is obscured by an opaque layer of clouds made up of sulfuric acid.
Planet Profile
Mass: 4,867,320,000,000,000 billion kg (0.815 x Earth)
Equatorial Diameter: 12,104 km
Polar Diameter: 12,104 km
Equatorial Circumference: 38,025 km
Known Moons: none
Notable Moons: none
Orbit Distance: 108,209,475 km (0.73 AU)
Orbit Period: 224.70 Earth days
Surface Temperature: 462 °C
First Record: 17th century BC
Recorded By: Babylonian astronomers
Size Of Venus Compared To The Earth
Facts About Venus
A day on Venus lasts longer than a year:
It takes 243 Earth days to rotate once on its axis. The planet’s orbit around the Sun takes 225 Earth days, compared to the Earth’s 365.
Venus is often called the Earth’s sister planet:
The Earth and Venus are very similar in size with only a 638 km difference in diameter, Venus having 81.5% of the Earth’s mass. Both also have a central core, a molten mantle and a crust.
Venus rotates counter-clockwise:
Also known as retrograde rotation. A possible reason might be a collision in the past with an asteroid or other object that caused the planet to alter its rotational path. It also differs from most other planets in our solar system by having no natural satellites.
Venus is the second brightest object in the night sky:
Only the Moon is brighter. With a magnitude of between -3.8 to -4.6 Venus is so bright it can be seen during daytime on a clear day.
Atmospheric pressure on Venus is 92 times greater than the Earth’s:
While its size and mass are similar to Earth, the small asteroids are crushed when entering its atmosphere, meaning no small craters lie on the surface of the planet. The pressure felt by a human on the surface would be equivalent to that experienced deep beneath the sea on Earth.
Venus is also known as the Morning Star and the Evening Star:
Early civilisations thought Venus was two different bodies, called Phosphorus and Hesperus by the Greeks, and Lucifer and Vesper by the Romans. This is because when its orbit around the Sun overtakes Earth’s orbit, it changes from being visible after sunset to being visible before sunrise. Mayan astronomers made detailed observations of Venus as early as 650 AD.
Venus is the hottest planet in our solar system:
The average surface temperature is 462 °C, and because Venus does not tilt on its axis, there is no seasonal variation. The dense atmosphere of around 96.5 percent carbon dioxide traps heat and causes a greenhouse effect.
A detailed study of Venus is currently underway:
In 2006, the Venus Express space shuttle was sent into orbit around Venus by the European Space Agency, and is sending back information about the planet. Originally planned to last five hundred Earth days, the mission has been extended several times. More than 1,000 volcanoes or volcanic centres larger than 20 km have been found on the surface of Venus.
The Russians sent the first mission to Venus:
The Venera 1 space probe was launched in 1961, but lost contact with base. The USA also lost their first probe to Venus, Mariner 1, although Mariner 2 was able to take measurements of the planet in 1962. The Soviet Union’s Venera 3 was the first man-made craft to land on Venus in 1966.
At one point it was thought Venus might be a tropical paradise:
The dense clouds of sulphuric acid surrounding Venus make it impossible to view its surface from outside its atmosphere. It was only when radio mapping was developed in the 1960s that scientists were able to observe and measure the extreme temperatures and hostile environment. It is thought Venus did once have oceans but these evaporated as the planets temperature increased.
Earth is the third planet from the Sun and is the largest of the terrestrial planets. Unlike the other planets in the solar system that are named after classic deities the Earth’s name comes from the Anglo-Saxon worderda which means ground or soil. The Earth was formed approximately 4.54 billion years ago and is the only known planet to support life.
Planet Profile
Mass: 5,972,190,000,000,000 billion kg
Equatorial Diameter: 12,756 km
Polar Diameter: 12,714 km
Equatorial Circumference: 40,030 km
Known Moons: 1
Notable Moons: The Moon
Orbit Distance: 149,598,262 km (1 AU)
Orbit Period: 365.26 Earth days
Surface Temperature: -88 to 58°C
Size Of The Earth Compared To The Moon
Facts About The Earth
The Earth’s rotation is gradually slowing:
This deceleration is happening almost imperceptibly, at approximately 17 milliseconds per hundred years, although the rate at which it occurs is not perfectly uniform. This has the effect of lengthening our days, but it happens so slowly that it could be as much as 140 million years before the length of a day will have increased to 25 hours.
The Earth was once believed to be the centre of the universe:
Due to the apparent movements of the Sun and planets in relation to their viewpoint, ancient scientists insisted that the Earth remained static, whilst other celestial bodies travelled in circular orbits around it. Eventually, the view that the Sun was at the centre of the universe was postulated by Copernicus, though this is also not the case.
Earth has a powerful magnetic field:
This phenomenon is caused by the nickel-iron core of the planet, coupled with its rapid rotation. This field protects the Earth from the effects of solar wind.
There is only one natural satellite of the planet Earth:
As a percentage of the size of the body it orbits, the Moon is the largest satellite of any planet in our solar system. In real terms, however, it is only the fifth largest natural satellite.
Earth is the only planet not named after a god:
The other seven planets in our solar system are all named after Roman gods or goddesses. Although onlyMercury, Venus, Mars, Jupiter and Saturn were named during ancient times, because they were visible to the naked eye, the Roman method of naming planets was retained after the discovery of Uranus andNeptune.
Of all the planets in our solar system, the Earth has the greatest density:
This varies according to the part of the planet; for example, the metallic core is denser than the crust. The average density of the Earth is approximately 5.52 grams per cubic centimetre.
Mars is the fourth planet from the Sun. Named after the Roman god of war, and often described as the “Red Planet” due to its reddish appearance. Mars is a terrestrial planet with a thin atmosphere composed primarily of carbon dioxide.
Mars Planet Profile
Mass: 641,693,000,000,000 billion kg (0.107 x Earth)
Equatorial Diameter: 6,805
Polar Diameter: 6,755
Equatorial Circumference: 21,297 km
Known Moons: 2
Notable Moons: Phobos & Deimos
Orbit Distance: 227,943,824 km (1.38 AU)
Orbit Period: 686.98 Earth days (1.88 Earth years)
Surface Temperature: -87 to -5 °C
First Record: 2nd millennium BC
Recorded By: Egyptian astronomers
Facts About Mars
Mars and Earth have approximately the same landmass:
Even though Mars has only 15% of the Earth’s volume and just over 10% of the Earth’s mass, around two thirds of the Earth’s surface is covered in water. Martian surface gravity is only 37% of the Earth’s (meaning you could leap nearly three times higher on Mars).
Mars is home to the tallest mountain in the solar system.
Olympus Mons, a shield volcano, is 21km high and 600km in diameter. Despite having formed over billions of years, evidence from volcanic lava flows is so recent many scientists believe it could still be active.
Only 18 missions to Mars have been successful
As of September 2014 there have been 40 missions to Mars, including orbiters, landers and rovers but not counting flybys. The most recent arrivals include the Mars Curiosity mission in 2012, the MAVEN mission, which arrived on September 22, 2014, followed by the Indian Space Research Organization’s MOM Mangalyaan orbiter, which arrived on September 24, 2014. The next missions to arrive will be the European Space Agency’s ExoMars mission, comprising an orbiter, lander, and a rover, followed by NASA’s InSight robotic lander mission, slated for launch in March 2016 and a planned arrival in September, 2016.”
Mars has the largest dust storms in the solar system:
They can last for months and cover the entire planet. The seasons are extreme because its elliptical (oval-shaped) orbital path around the Sun is more elongated than most other planets in the solar system.
On Mars the Sun appears about half the size as it does on Earth:
At the closest point to the Sun, the Martian southern hemisphere leans towards the Sun, causing a short, intensely hot summer, while the northern hemisphere endures a brief, cold winter: at its farthest point from the Sun, the Martian northern hemisphere leans towards the Sun, causing a long, mild summer, while the southern hemisphere endures a lengthy, cold winter.
Pieces of Mars have fallen to Earth:
Scientists have found tiny traces of Martian atmosphere within meteorites violently ejected from Mars, then orbiting the solar system amongst galactic debris for millions of years, before crash landing on Earth. This allowed scientists to begin studying Mars prior to launching space missions.
Mars takes its name from the Roman god of war:
The ancient Greeks called the planet Ares, after their god of war; the Romans then did likewise, associating the planet’s blood-red colour with Mars, their own god of war. Interestingly, other ancient cultures also focused on colour – to China’s astronomers it was ‘the fire star’, whilst Egyptian priests called on ‘Her Desher’, or ‘the red one’. The red colour Mars is known for is due to the rock and dust covering its surface being rich in iron.
THE MAJOR PLANETS(non terrestrial planets)
The outer planets (sometimes called Jovian planets or gas giants) are huge planets swaddled in gas. They all have rings and all of plenty of moons each. Despite their size, only two of them are visible without telescopes: Jupiter and Saturn. Uranus and Neptune were the first planets discovered since antiquity, and showed astronomers the solar system was bigger than previously thought. The outer planets are further away, larger and made up mostly of gas.
JUPITER
The planet Jupiter is the fifth planet out from the Sun, and is two and a half times more massive than all the other planets in the solar system combined. It is made primarily of gases and is therefore known as a “gas giant”.
Jupiter Planet Profile
Mass: 1,898,130,000,000,000,000 billion kg (317.83 x Earth)
Equatorial Diameter: 142,984 km
Polar Diameter: 133,709 km
Equatorial Circumference: 439,264 km
Known Moons: 67
Notable Moons: Io, Europa, Ganymede, & Callisto more info
Known Rings: 4
Orbit Distance: 778,340,821 km (5.20 AU)
Orbit Period: 4,332.82 Earth days (11.86 Earth years)
Surface Temperature: -108°C
First Record: 7th or 8th century BC
Recorded By: Babylonian astronomers
Size Of Jupiter Compared To The Earth
Facts About Jupiter
Jupiter is the fourth brightest object in the solar system:
Only the Sun, Moon and Venus are brighter. It is one of five planets visible to the naked eye from Earth.
The ancient Babylonians were the first to record their sightings of Jupiter:
This was around the 7th or 8th century BC. Jupiter is named after the king of the Roman gods. To the Greeks, it represented Zeus, the god of thunder. The Mesopotamians saw Jupiter as the god Marduk and patron of the city of Babylon. Germanic tribes saw this planet as Donar, or Thor.
Jupiter has the shortest day of all the planets:
It turns on its axis once every 9 hours and 55 minutes. The rapid rotation flattens the planet slightly, giving it an oblate shape.
Jupiter orbits the Sun once every 11.8 Earth years:
From our point of view on Earth, it appears to move slowly in the sky, taking months to move from one constellation to another.
Jupiter has unique cloud features:
The upper atmosphere of Jupiter is divided into cloud belts and zones. They are made primarily of ammonia crystals, sulfur, and mixtures of the two compounds.
The Great Red Spot is a huge storm on Jupiter:
It has raged for at least 350 years. It is so large that three Earths could fit inside it.
Jupiter’s interior is made of rock, metal, and hydrogen compounds:
Below Jupiter’s massive atmosphere (which is made primarily of hydrogen), there are layers of compressed hydrogen gas, liquid metallic hydrogen, and a core of ice, rock, and metals.
Jupiter’s moon Ganymede is the largest moon in the solar system:
Jupiter’s moons are sometimes called the Jovian satellites, the largest of these are Ganymeade, Callisto Io and Europa. Ganymeade measures 5,268 km across, making it larger than the planet Mercury.
Jupiter has a thin ring system:
Its rings are composed mainly of dust particles ejected from some of Jupiter’s smaller worlds during impacts from incoming comets and asteroids. The ring system begins some 92,000 kilometres above Jupiter’s cloud tops and stretches out to more than 225,000 km from the planet. They are between 2,000 to 12,500 kilometres thick.
Eight spacecraft have visited Jupiter:
Pioneer 10 and 11, Voyager 1 and 2, Galileo, Cassini, Ulysses, and New Horizons missions. The Juno mission is its way to Jupiter and will arrive in July 2016. Other future missions may focus on the Jovian moons Europa, Ganymede, and Callisto, and their subsurface oceans.
SATURN
Saturn is the sixth planet from the Sun and the most distant that can be seen with the naked eye. It is best known for its fabulous ring system that was discovered in 1610 by the astronomer Galileo Galilei.
Planet Profile
Mass: 568,319,000,000,000,000 billion kg (95.16 x Earth)
Equatorial Diameter: 120,536 km
Polar Diameter: 108,728 km
Equatorial Circumference: 365,882 km
Known Moons: 62
Notable Moons: Titan, Rhea & Enceladus more info
Known Rings: 30+ (7 Groups)
Orbit Distance: 1,426,666,422 km (9.58 AU)
Orbit Period: 10,755.70 Earth days (29.45 Earth years)
Surface Temperature: -139 °C
First Record: 8th century BC
Recorded By: Assyrians
Size Of Saturn Compared To The Earth
Facts About Saturn
Saturn can be seen with the naked eye:
It is the fifth brightest object in the solar system and is also easily studied through binoculars or a small telescope.
Saturn was known to the ancients, including the Babylonians and Far Eastern observers:
It is named for the Roman god Saturnus, and was known to the Greeks as Cronus.
Saturn is the flattest planet:
Its polar diameter is 90% of its equatorial diameter, this is due to its low density and fast rotation. Saturn turns on its axis once every 10 hours and 34 minutes giving it the second-shortest day of any of the solar system’s planets.
Saturn orbits the Sun once every 29.4 Earth years:
Its slow movement against the backdrop of stars earned it the nickname of “Lubadsagush” from the ancient Assyrians. The name means “oldest of the old”.
Saturn’s upper atmosphere is divided into bands of clouds:
The top layers are mostly ammonia ice. Below them, the clouds are largely water ice. Below are layers of cold hydrogen and sulfur ice mixtures.
Saturn has oval-shaped storms similar to Jupiter’s:
The region around its north pole has a hexagonal-shaped pattern of clouds. Scientists think this may be a wave pattern in the upper clouds. The planet also has a vortex over its south pole that resembles a hurricane-like storm.
Saturn is made mostly of hydrogen:
It exists in layers that get denser farther into the planet. Eventually, deep inside, the hydrogen becomes metallic. At the core lies a hot interior.
Saturn has the most extensive rings in the solar system:
The Saturnian rings are made mostly of chunks of ice and small amounts of carbonaceous dust. The rings stretch out more than 120,700 km from the planet, but are are amazingly thin: only about 20 meters thick.
Saturn has 150 moons and smaller moonlets:
All are frozen worlds. The largest moons are Titan and Rhea. Enceladus appears to have an ocean below its frozen surface.
Titan is a moon with complex and dense nitrogen-rich atmosphere:
It is composed mostly of water ice and rock. Its frozen surface has lakes of liquid methane and landscapes covered with frozen nitrogen. Planetary scientists consider Titan to be a possible harbour for life, but not Earth-like life.
Four spacecraft have visited Saturn:
Pioneer 11, Voyager 1 and 2, and the Cassini-Huygens mission have all studied the planet. Cassini continues to orbit Saturn, sending back a wealth of data about the planet, its moons, and rings.
URANUS
Uranus is the seventh planet from the Sun. It’s not visible to the naked eye, and became the first planet discovered with the use of a telescope. Uranus is tipped over on its side with an axial tilt of 98 degrees. It is often described as “rolling around the Sun on its side.”
Uranus Planet Profile
Mass: 86,810,300,000,000,000 billion kg (14.536 x Earth)
Equatorial Diameter: 51,118 km
Polar Diameter: 49,946 km
Equatorial Circumference: 159,354 km
Known Moons: 27
Notable Moons: Oberon, Titania, Miranda, Ariel & Umbriel more info
Known Rings: 13
Orbit Distance: 2,870,658,186 km (19.22 AU)
Orbit Period: 30,687.15 Earth days (84.02 Earth years)
Surface Temperature: -197 °C
Discover Date: March 13th 1781
Discovered By: William Herschel
Size Of Uranus Compared To The Earth
Facts About Uranus
Uranus was officially discovered by Sir William Herschel in 1781:
It is too dim to have been seen by the ancients. At first Herschel thought it was a comet, but several years later it was confirmed as a planet. Herscal tried to have his discovery named “Georgian Sidus” after King George III. The name Uranus was suggested by astronomer Johann Bode. The name comes from the ancient Greek deity Ouranos.
Uranus turns on its axis once every 17 hours, 14 minutes:
The planet rotates in a retrograde direction, opposite to the way Earth and most other planets turn.
Uranus makes one trip around the Sun every 84 Earth years:
During some parts of its orbit one or the other of its poles point directly at the Sun and get about 42 years of direct sunlight. The rest of the time they are in darkness.
Uranus is often referred to as an “ice giant” planet:
Like the other gas giants, it has a hydrogen upper layer, which has helium mixed in. Below that is an icy “mantle, which surrounds a rock and ice core. The upper atmosphere is made of water, ammonia and the methane ice crystals that give the planet its pale blue color.
Uranus is the Coldest Planet:
With minimum atmospheric temperature of -224°C Uranus is the coldest planet in the solar system. The upper atmosphere of Uranus is covered by a methane haze. This hides the storms that take place in the cloud decks.
Uranus has two sets of rings of very thin set of dark colored rings:
The ring particles are small, ranging from a dust-sized particles to small boulders. There are nine inner rings and two outer rings. They probably formed when one or more of Uranus’s moons were broken up in an impact. The first set of rings was discovered in 1977 and the second set was discovered in 2003 by the Hubble Space Telescope.
Uranus’ moons are named after characters created by William Shakespeare and Alaxander Pope:
These include Oberon, Titania and Miranda. All are frozen worlds with dark surfaces. Some are ice and rock mixtures. The most interesting Uranian moon is Miranda; it has ice canyons, terraces, and other strange-looking surface areas.
Only one spacecraft has flown by Uranus:
In 1986, the Voyager 2 spacecraft swept past the planet at a distance of 81,500 km. It returned the first close-up images of the planet, its moons, and rings.
NEPTUNE
Neptune is the eighth planet from the Sun and is the most distant planet from the Sun. This gas giantplanet may have formed much closer to the Sun in early solar system history before migrating to its present position.
Planet Profile
Mass: 102,410,000,000,000,000 billion kg (17.15x Earth)
Equatorial Diameter: 49,528 km
Polar Diameter: 48,682 km
Equatorial Circumference: 155,600 km
Known Moons: 14
Notable Moons: Triton more info
Known Rings: 5
Orbit Distance: 4,498,396,441 km (30.10 AU)
Orbit Period: 60,190.03 Earth days (164.79 Earth years)
Surface Temperature: -201 °C
Discover Date: September 23rd 1846
Discovered By: Urbain Le Verrier & Johann Galle
Size Of Neptune Compared To The Earth
Facts About Neptune
Neptune was not known to the ancients:
It is not visible to the naked eye and was first observed in 1846. Its position was determined using mathematical predictions. It was named after the Roman god of the sea.
Neptune spins on its axis very rapidly:
Its equatorial clouds take 18 hours to make one rotation. This is because Neptune is not solid body.
Neptune makes one trip around the Sun every 164.8 Earth years:
During some parts of its orbit one or the other of its poles point directly at the Sun and get about 42 years of direct sunlight. The rest of the time they are in darkness.
Neptune is the smallest of the ice giants:
Despite being smaller than Uranus, Neptune has a greater mass. Below its heavy atmosphere, Uranus is made of layers of hydrogen, helium, and methane gases. They enclose a layer of water, ammonia and methane ice. The inner core of the planet is made of rock.
The atmosphere of Neptune is made of hydrogen and helium, with some methane:
The methane absorbs red light, which makes the planet appear a lovely blue. High, thin clouds drift in the upper atmosphere.
Neptune has a very active climate:
Large storms whirl through its upper atmosphere, and high-speed winds track around the planet at up 600 meters per second. One of the largest storms ever seen was recorded in 1989. It was called the Great Dark Spot. It lasted about five years.
Neptune has a very thin collection of rings:
They are likely made up of ice particles mixed with dust grains and possibly coated with a carbon-based substance.
Neptune has 14 moons:
The most interesting moon is Triton, a frozen world that is spewing nitrogen ice and dust particles out from below its surface. It was likely captured by the gravitational pull of Neptune. It is probably the coldest world in the solar system.
Only one spacecraft has flown by Neptune:
In 1989, the Voyager 2 spacecraft swept past the planet. It returned the first close-up images of the Neptune system. The NASA/ESA Hubble Space Telescope has also studied this planet, as have a number of ground-based telescopes.
PLUTO
Discovered in 1930, Pluto is the second closest dwarf planet to the Sun and was at one point classified as the ninth planet. Pluto is also the second most massive dwarf planet with Eris being the most massive.
Pluto Dwarf Planet Profile
Mass: 13,050,000,000,000 billion kg (0.00218 x Earth)
Diameter: 2,368 km (+- 20km)
Known Moons: 5
Notable Moons: Charon, Nix, Hydra, Kerberos and Styx more info
Orbit Distance: 5,874,000,000 km (39.26 AU)
Orbit Period: 246.04 Earth years
Surface Temperature: -229°C
Discovery Date: 18th February 1930
Discovered By: Clyde W. Tombaugh
Size Of Pluto Compared To The Earth
Facts About Pluto
Pluto is named after the Greek god of the underworld:
This is a later name for the more well known Hades and was proposed by Venetia Burney an eleven year old schoolgirl from Oxford, England.
Pluto was reclassified from a planet to a dwarf planet in 2006:
This is when the IAU formalised the definition of a planet as “A planet is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit.”
Pluto was discovered on February 18th, 1930 by the Lowell Observatory:
For the 76 years between Pluto being discovered and the time it was reclassified as a dwarf planet it completed under a third of its orbit around the Sun.
Pluto has five known moons:
They are Charon (discovered in 1978,), Hydra and Nix (both discovered in 2005), Kerberos originally P4 (discovered 2011) and Styx originally P5 (discovered 2012) official designations S/2011 (134340) 1 and S/2012 (134340) 1.
Pluto may be the largest dwarf planet:
Or it could be Eris. Currently the most accurate measurements give Eris an average diameter of 2,326km with a margin of error of 12km, while Pluto’s diameter is 2,368km with a 20km margin of error, however due to Pluto’s atmosphere it is difficult to say for certain.
Pluto is smaller than a number of moons:
These are Ganymede, Titan, Callisto, Io, Europa, Triton, and the Earth’s moon. Pluto has 66% of the diameter of the Earth’s moon and 18% of its mass.
Pluto has a eccentric and inclined orbit:
This takes it between 4.4 and 7.4 billion km from the Sun meaning Pluto is periodically closer to the Sun than Neptune.
No spacecraft have visited Pluto:
Though in July 2015 the spacecraft New Horizons, which was launched in 2006, is scheduled to fly by Pluto on its way to the Kuiper Belt.
Pluto’s location was predicted by Percival Lowell in 1915:
The prediction came from deviations he initially observed in 1905 in the orbits of Uranus and Neptune.
Pluto sometimes has an atmosphere:
During Pluto’s elliptical when Pluto is closer to the Sun its surface ice thaws and forms a thin atmosphere primarily of nitrogen with a little methane and carbon monoxide. When Pluto travels away from the Sun the atmosphere then freezes back to its solid state.
MOON
The Moon (or Luna) is the Earth’s only natural satellite and was formed 4.6 billion years ago around some 30–50 million years after the formation of the solar system. The Moon is in synchronous rotation with Earth meaning the same side is always facing the Earth. The first unmanned mission to the Moon was in 1959 by the Soviet Lunar Program with the first manned landing being Apollo 11 in 1969.
Moon Profile
Circumference at Equator: 10,917.0 km
Diameter: 3,475 km
Mass: 73,476,730,924,573,500 million kg (0.0123 x Earth)
Orbits: The Earth
Average Distance from Earth: 384,400 km
Length of Orbit: 27.3 Earth days
Surface Temperature: -233 to 123 °C
Size Of The Moon Compared To The Earth
Facts About The Moon
The dark side of the moon is a myth:
In reality both sides of the Moon see the same amount of sunlight however only one face of the Moon is ever seen from Earth this is because the Moon rotates around on its own axis in exactly the same time it takes to orbit the Earth, meaning the same side is always facing the Earth. The side we see is lit by reflected sunlight, while the side facing away from Earth lies in darkness and has only been seen by the human eye from a spacecraft.
The rise and fall of the tides on Earth is caused by the Moon:
There are two bulges in the Earth due to the gravitational pull that the Moon exerts; one on the side facing the Moon, and the other on the opposite side that faces away from the Moon, The bulges move around the oceans as the Earth rotates, causing high and low tides around the globe.
The Moon is drifting away from the Earth:
The Moon is moving approximately 3.8 cm away from our planet every year. It is estimated that it will continue to do so for around 50 billion years. By the time that happens, the Moon will be taking around 47 days to orbit the Earth instead of the current 27.3 days.
A person would weigh much less on the Moon:
The Moon has much weaker gravity than Earth, due to its smaller mass, so you would weigh about one sixth (16.5%) of your weight on Earth. This is why the lunar astronauts could leap and bound so high in the air.
The Moon has only been walked on by 12 people; all American males:
The first man to set foot on the Moon in 1969 was Neil Armstrong on the Apollo 11 mission, while the last man to walk on the Moon in 1972 was Gene Cernan on the Apollo 17 mission. Since then the Moon has only be visited by unmanned vehicles.
The Moon has no atmosphere:
This means that the surface of the Moon is unprotected from cosmic rays, meteorites and solar winds, and has huge temperature variations. The lack of atmosphere means no sound can be heard on the Moon, and the sky always appears black.
The Moon has quakes:
These are caused by the gravitational pull of the Earth. Lunar astronauts used seismographs on their visits to the Moon, and found that small moonquakes occurred several kilometres beneath the surface, causing ruptures and cracks. Scientists think the Moon has a molten core, just like Earth.
The first spacecraft to reach the Moon was Luna 1 in 1959:
This was a Soviet craft, which was launched from the USSR. It passed within 5995 km of the surface of the Moon before going into orbit around the Sun.
The Moon is the fifth largest natural satellite in the Solar System:
At 3,475 km in diameter, the Moon is much smaller than the major moons of Jupiter and Saturn. Earth is about 80 times the volume than the Moon, but both are about the same age. A prevailing theory is that the Moon was once part of the Earth, and was formed from a chunk that broke away due to a huge object colliding with Earth when it was relatively young.
The Moon will be visited by man in the near future:
NASA plans to return astronauts to the moon to set up a permanent space station. Mankind may once again walk on the moon in 2019, if all goes according to plan.
During the 1950’s the USA considered detonating a nuclear bomb on the Moon:
The secret project was during the height cold war was known as “A Study of Lunar Research Flights” or “Project A119″ and meant as a show of strength at a time they were lagging behind in the space race.
Phases Of The Moon
COMET
What Is A Comet?
A comet is a very small solar system body made mostly of ices mixed with smaller amounts of dust and rock. Most comets are no larger than a few kilometres across. The main body of the comet is called the nucleus, and it can contain water, methane, nitrogen and other ices.
When a comet is heated by the Sun, its ices begin to sublimate (similar to the way dry ice “fizzes” when you leave it in sunlight). The mixture of ice crystals and dust blows away from the comet nucleus in the solar wind, creating a pair of tails. The dust tail is what we normally see when we view comets from Earth.
A plasma tail also forms when molecules of gas are “excited” by interaction with the solar wind. The plasma tail is not normally seen with the naked eye, but can be imaged. Comets normally orbit the Sun, and have their origins in the Oort Cloud and Kuiper Belt regions of the outer solar system.
Comet Naming
Comets come in several categories. The most common are periodic and non-periodic.
In the past, comets were named for their discoverers, such as Comet Halley for Sir Edmond Halley. In modern times, comet names are governed by rules set forth by the International Astronomical Union (IAU). A comet is given an official designation, and can also be identified by the last names of up to three independent discoverers.
Here’s how it works. Once a comet has been confirmed, the following naming rules are followed. First, if the comet is a periodic comet, then it is indicated with a P/ followed by the year of its discovery, a letter indicating the half-month in which it was discovered, followed by a number indicating its order of discovery. So, for example, the second periodic comet found in the first half of January, 2015 would be called P/2015 A2.
A non-periodic comet would be indicated with a C/ followed by the year of its discovery, a letter indicating the half-month in which it was discovered, followed by a number indicating its order of discovery.
If a comet is independently discovered by three people named Smith, Jones, and Petersen, it could also be called Comet Smith-Jones-Petersen, in addition to its formal designation. Today, many comets are found through automated instrument searches, and so the formal designations are more commonly used.
Famous Comets
Well-known comets include the non-periodic comets Hale-Bopp (C/1995 O1), Hyakutake (C/1996 B2), McNaught (C2006 P1), and Lovejoy (C/2011 W3). These flared brightly in our skies and then faded into obscurity.
In addition, Comet Shoemaker-Levy 9 (D/1993 F2) was spotted after it had broken up after a close call with Jupiter. (The D in its proper designation means it has disappeared or is determined to no longer exist). More than a year later, the pieces of the comet crashed into Jupiter.
The periodic Comet Halley (1P/Halley) is the most famous in history. It returns to the inner solar system once every 76 years. Other well-known periodic comets include 2P/Encke, which appears ever 3.3 years and 9P/Tempel (Tempel 2), which was visited by the Deep Impact and Stardust probes, and makes perihelion around the Sun every 5.5 years.
Facts About Comets
There are many misconceptions about comets, which are simply pieces of solar system ices travelling in orbit around the Sun. Here are some fascinating and true facts about comets.
- The nucleus of a comet is made of ice and can be as small as a few meters across to giant boulders a few kilometres across.
- The closest point in a comet’s orbit to the Sun is called “perihelion”. The most distant point is called “aphelion”.
- As a comet gets closer to the Sun, it begins to experience heat. That causes some of its ices to sublimate (similar to dry ice sizzling in sunlight). If the ice is close to the comet’s surface, it may form a small “jet” of material spewing out from the comet like a mini-geyser.
- Material streams from comets and populates the comet’s orbit. If Earth (or another planet) happens to move through that stream, those particles fall to Earth as meteor showers.
- As a comet gets close to the Sun, it loses some of its mass due to the sublimation. If a comet goes around enough times, it will eventually break up. Comets also break up if they come TOO close to the Sun or another planet in their orbits.
- Comets are usually made of frozen water and supercold methane, ammonia and carbon dioxide ices. Those are mixed with rock, dust, and other metallic bits of solar system debris.
- Comets have two tails: a dust tail (which you can see with the naked eye) and a plasma tail, which is easily photographed but difficult to see with your eyes.
- Comet orbits are usually elliptical.
- Many comets formed in the Oort Cloud and Kuiper Belts, two of the outermost regions of the solar system.
- Comets are not spaceships or alien bases. They are fascinating bits of solar system material that date back to the formation of the Sun and planets.
SUN
The Sun or Sol, is the star at the centre of our solar system and is responsible for the Earth’s climate and weather. The Sun is an almost perfect sphere with a difference of just 10km in diameter between the poles and the equator. The average radius of the Sun is 695,508 km (109.2 x that of the Earth) of which 20–25% is the core.
Star Profile
Age: 4.6 Billion Years
Type: Yellow Dwarf (G2V)
Diameter: 1,392,684 km
Circumference at Equator: 4,370,005.6 km
Mass: 1,989,100,000,000,000,000,000 billion kg (333,060 x Earth)
Surface Temperature: 5500 °C
Size Of The Sun
Facts About The Sun
One million Earths could fit inside the Sun:
If a hollow Sun was filled up with spherical Earths then around 960,000 would fit inside. On the other hand if these Earths were squished inside with no wasted space then around 1,300,000 would fit inside. The Sun’s surface area is 11,990 times that of the Earth’s.
Eventually, the Sun will consume the Earth:
When all the Hydrogen has been burned, the Sun will continue for about 130 million more years, burning Helium, during which time it will expand to the point that it will engulf Mercury and Venus and the Earth. At this stage it will have become a red giant
The Sun will one day be about the size of Earth:
After its red giant phase, the Sun will collapse, retaining its enormous mass, but containing the approximate volume of our planet. When this happens, it will be called a white dwarf.
The Sun contains 99.86% of the mass in the Solar System:
The mass of the Sun is approximately 330,000 times greater than that of Earth. It is almost three quarters Hydrogen, whilst most of the remaining mass is Helium.
The Sun is an almost perfect sphere:
There is only a 10 kilometre difference in its polar diameter compared to its equatorial diameter. Considering the vast expanse of the Sun, this means it is the closest thing to a perfect sphere that has been observed in nature.
Light from the Sun takes eight minutes to reach Earth:
With a mean average distance of 150 million kilometres from Earth and with light travelling at 300,000 kilometres per second, dividing one by the other gives us an approximate time of 500 seconds, or eight minutes and 20 seconds. Although this energy reaches Earth in a few minutes, it will already have taken millions of years to travel from the Sun’s core to its surface.
The Sun travels at 220 kilometres per second:
The Sun is 24,000-26,000 light years from the galactic centre and it takes the Sun 225-250 million years to complete an orbit of the centre of the Milky Way.
The distance from the Sun to Earth changes throughout the year:
Because the Earth travels on an elliptical orbit around the Sun, the distance between the two bodies varies from 147 to 152 million kilometres. The distance between the Earth and the Sun is called an Astronomical Unit (AU).
The Sun is middle-aged:
At around 4.5 billion years old, the Sun has already burned off about half of its store of Hydrogen. It has enough left to continue to burn Hydrogen for approximately another 5 billion years. The Sun is currently a type of star known as a Yellow Dwarf
The Sun has a very strong magnetic field:
Solar flares occur when magnetic energy is released by the Sun during magnetic storms, which we see as sunspots. In sunspots, the magnetic lines are twisted and they spin, much like a tornado would on Earth.
The temperature inside the Sun can reach 15 million degrees Celsius:
At the Sun’s core, energy is generated by nuclear fusion, as Hydrogen converts to Helium. Because hot objects generally expand, the Sun would explode like a giant bomb if it weren’t for its enormous gravitational force.
The Sun generates solar wind:
This is a stream of charged particles, which travels through the Solar System at approximately 450 kilometres per second. Solar wind occurs where the magnetic field of the Sun extends into space instead of following its surface.
Satellites
Name Distance from Sun Type
Mercury 57,909,227 km (0.39 AU) Planet
Venus 108,209,475 km (0.73 AU) Planet
Earth 149,598,262 km (1 AU) Planet
Mars 227,943,824 km (1.38 AU) Planet
Ceres 413,700,000 km (2.77 AU) Dwarf Planet
Jupiter 778,340,821 km (5.20 AU) Planet
Saturn 1,426,666,422 km (9.58 AU) Planet
Uranus 2,870,658,186 km (19.22 AU) Planet
Neptune 4,498,396,441 km (30.10 AU) Planet
Pluto 5,874,000,000 km (39.26 AU) Dwarf Planet
Haumea 6,452,000,000 km (43.13 AU) Dwarf Planet
Makemake 6,850,000,000 km (45.79 AU) Dwarf Planet
Eris 10,120,000,000 km (68.01 AU) Dwarf Planet
ASTEROID BELT
What Is The Asteroid Belt?
The vast majority of asteroids in the solar system are found in a region of the solar system out beyond Mars. They form the Asteroid Belt. Others orbit in near-Earth space and a few migrate or are thrown out to the outer solar system by gravitational interactions. The four largest asteroids in the belt are Ceres, Vesta, Pallas, and Hygiea. They contain half the mass of the entire belt. The rest of the mass is contained in countless smaller bodies. There was a theory once that if you combined all the asteroids they would make up the missing “Fifth” rocky planet. Planetary scientists estimate that if you could put all that material together that exists there today, it would make a tiny world smaller than Earth’s moon.
Where Is The Asteroid Belt Located?
The Asteroid Belt is located in an area of space between the orbits of Mars and Jupiter. That places it between 2.2 and 3.2 astronomical units (AU) from the Sun. The belt is about 1 AU thick. The average distance between objects in the Asteroid Belt is quite large. If you could stand on an asteroid and look around, the next one would be too far away to see very well.
Various Asteroids – www.nasa.gov/centers/jpl/news/dawn20110718.html
Asteroid Mining
The solar system contains many different types of asteroids, grouped by the minerals they contain. The abundances of precious metals such as nickel, iron, and titanium (to name a few), and water make asteroids an attractive target for mining operations when humans decide to expand their presence through interplanetary space. For example, water from asteroids could serve colonies in space, while the minerals and metals would be used to build habitats and grow food for future space colony inhabitants. Beginning 2013, companies interested in asteroid mining began announcing their plans for future operations on distant planetoids. In addition, NASA is looking into similar missions. The biggest obstacles to asteroid mining are the need to develop affordable spaceflight technology that would allow humans to get to the asteroids of interest.
Facts About The Asteroid Belt
What other fascinating things do we know about the Asteroid Belt?
- Asteroid Belt objects are made of rock and stone. Some are solid objects, while others are orbiting “rubble piles”.
- The Asteroid Belt contains billions and billions of asteroids.
- Some asteroids in the Belt are quite large, but most range in size down to pebbles.
- The asteroid 1/Ceres is also designated as a dwarf planet, the largest one in the inner solar system.
- We know of at least 7,000 asteroids.
- The Asteroid Belt may contain many objects, but they are spread out over a huge area of space. This has allowed spacecraft to move through this region without hitting anything.
- Asteroids get their names from suggestions by their discoverers and are also given a number.
- The formation of Jupiter disrupted the formation of any worlds in the Asteroid Belt region by scattering asteroids away. This caused them to collide and break into smaller pieces.
- Gravitational influences can move asteroids out of the Belt.
- The Asteroid Belt is often referred to as the “Main Belt” to distinguish it from other groups of asteroids such as the Lagrangians and Centaurs.
Oort Cloud Illustration – laurinemoreau.com
What Is The Oort Cloud?
The Oort Cloud is an extended shell of icy objects that exist in the outermost reaches of the
solar system. It is named after astronomer Jan Oort, who first theorized its existence. The Oort Cloud is roughly spherical, and is the origin of most of the long-period
comets that have been observed.
This cloud of particles is theorized to be the remains of the disc of material that formed the
Sun and
planets. Astronomers now refer to those primeval objects as a protoplanetary disk. The most likely theory is that the material now in the Oort Cloud probably formed closer to the young Sun in the earliest epochs of solar system formation. As the planets grew, and in particular as
Jupiter coalesced and migrated to its present position, its gravitational influence is thought to have scattered many icy objects out to their present position in the Oort cloud.
The Oort Cloud is very distant from the Sun and it can be disrupted by the nearby passage of a star, nebula, or by actions in the disk of the Milky Way. Those actions knock cometary nuclei out of their orbits, and send them on a headlong rush toward the Sun.
Oort Cloud Location
The inner limits of the Oort Cloud begin at about 2,000 AU from the Sun. The cloud itself stretches out almost a quarter of the way to the nearest star, Proxima Centauri. It is spherically shaped and consists of an outer cloud and a torus (doughnut-shaped) inner cloud.
Facts About The Oort Cloud
- Objects in the Oort Cloud are also referred to as Trans-Neptunian objects. This name also applies to objects in the Kuiper Belt.
- Some astronomers theorize that the Sun may have captured Oort Cloud cometary material from the outer disks of other stars that were forming in the same nebula as our star.
- The Oort Cloud is a reserve of cometary nuclei that contain ices dating back to the origin of the solar system.
- No one knows for sure how many objects exist in the Oort Cloud, but most estimates put it at around 2 trillion.
- The planetoid Sedna, discovered in 2003, is thought to be a member of the inner Oort Cloud.
- Astronomers think that long-period comets (those with orbital periods longer than 200 years) have their origins in the Oort Cloud.
Chondrit Meteorite – http://commons.wikimedia.org/wiki/File:Chondrite_H5.JPG
What Is A Meteorite?
Earth is bombarded with millions of tons of space material each day. Most of the objects vaporize in our atmosphere, but some of the larger pieces (from pebbles to boulder-sized rocks) actually fall to the ground. Most of the objects come from asteroids, which are objects made of various types of rock and have existed since the origin of the solar system. A small rocky or metallic chunk of material that travels through space is called a meteoroid. Very small meteoroids (the size of dust) are often referred to as micrometeoroids or space dust. These fragments may also be leftover comet debris, or were ejected in collisions between other solar system bodies such as the Moon or Mars.
As a meteoroid travels through our atmosphere, it is heated by friction. That causes it to glow, and if this happens at night, we see a long streak of light known as a meteor.
If the object survives the trip and falls to Earth’s surface, it is known as a meteorite. Many of these fall into the ocean (since about 71% of Earth’s surface is covered by water). The rest fall on land, where they await discovery by meteorite hunters.
Types Of Meteorites
Meteorites are fragments of asteroids that fall to ground on Earth. Scientists classify these objects according to their chemical makeup (what chemicals exist in them), their isotopic compositions (the types of each chemical element they contain), and their mineralogy (the minerals they contain).
Beyond those classifications, meteorites are also sorted as stony (made of rocky material), metallic (whether they contain iron), and mixtures (stony-irons). Those three classes can be divided even further. For example, pallasite meteorites are a class of stony-iron meteorites that are made mostly of nickel and iron, but also contain olivine crystals (a commonly found crystal on Earth).
Famous Meteorites
Over the course of Earth’s history, many meteorites (large and small) have fallen to our planet’s surface. The most famous are the Allende, the Fukang, Hoba, and the Willamette Meteorite.
The Allende Meteorite fell to Earth in a fireball on February 8, 1969. It was originally about the size of a car, and pieces were strewn across the Mexican state of Chihuahua. It has become one of the most-studied meteorites of all time, and is an excellent example of a carbonaceous chondrite. These types of meteorites date back to the formation of the Sun and Planets, and are among the most primitive solar system materials around. They are made mostly of silicates, oxides, sulfides, water, organic compounds and various minerals.
The Fukang Meteorite is one of the best examples of a pallasite, a type of stony-iron meteorite. Because of its large gem-like olivine crystals, pieces of this meteorite are much in demand by collectors.
The Hoba Meteorite was found in Namibia (in Africa). It is a very large, 60-tone rock, which makes it nearly impossible to move. It has been declared a National Monument in Namibia, and is one of the rare meteorites that is also part of a tourist site. Meteorite experts think Hoban fell about 80,000 years ago. It is mostly iron, with some nickel and traces of other elements.
The Willamette Meteorite weighs 15.5 tons and is the largest ever found in the United States.
Facts About Meteorites
- Millions of meteoroids travel through Earth’s atmosphere each day.
- When a meteor encounters our atmosphere and is vaporized, it leaves behind a trail. That “burning” meteoroid is called a meteor.
- The appearance of a number of meteors occurring in the same part of the sky over a period of time is called “meteor shower”.
- Many meteor showers are associated with comets, which leave behind debris as they orbit through the solar system. Showers occur when Earth’s orbit crosses the path of a comet’s orbit.
- Most meteorites are one of three types: stony, stony-iron, or iron. These compositions tell us where the meteoroid existed in its parent body. An iron or stony iron was close to the core of an asteroid, while a stony object was closer to the surface.
METEOR SHOWER FACTs
Geminid Meteor Shower – http://apod.nasa.gov/apod/ap131213.html
What Is A Meteor Shower?
A meteor shower occurs when a number of meteors flash seem to radiate (or shoot out from) the same point in the sky. They are usually named for the constellation in which their radiant appears. The meteoroids in a shower usually come from the trail of debris left behind by a comet. In the case of the Geminids and Quadrantids, those meteor showers come from the debris scatted by orbiting asteroids. When Earth’s orbit intersects the dust trail, we see more meteors flaring as the cometary debris encounters our planet’s atmosphere.
Famous Meteor Showers
There are several famous and easy-to-observe meteor showers. The Perseids occur in mid-August when Earth encounters the debris trail from Comet Swift-Tuttle. They appear to radiate from a point in the constellation Perseus. The shower lasts from mid-July to late August, with a peak around August 12th each year.
The Leonid meteor shower can be a very busy one. It occurs each year in mid-November, and rains debris from Comet 55P/Tempel-Tuttle. In 1833, observers estimated that hundreds of thousands of meteors flared through the sky. Observers wait for it each year, hoping for another spectacular show, emanating from the direction of the constellation Leo.
The Geminid meteor shower occurs in December, when Earth crosses the path of the asteroid 3200 Phaethon. The meteors appear to come from the direction of the constellation Gemini, and observers have noted that they move more slowly than other meteors.
In late April, the Lyrids bring pieces of comet C/1861 G1/Thatcher back to Earth, which seem to radiate from the constellation Lyra. The peak of this storm is around April 22. Every 60 years or so this shower becomes more intense.
When Is The Next Meteor Shower?
There are 21 meteor showers throughout the year. They occur mostly between April and December. Forecasts about meteor showers can be found at:
Facts About Meteor Showers
- Most meteor showers are caused by debris from comets. When Earth moves through those debris trails, we see increased numbers of comets.
- Two meteor showers are caused by debris shed by asteroids. The Quadrantids are very likely caused by debris from the minor planet 2003 EH1. The Geminid meteor shower comes from debris shed by asteroid 3200 Phaethon.
- The Orionid Meteor shower (which occurs in late October each year) is created by dust and debris left behind by the passage of Comet 1P/Halley.
- Meteors fall to Earth during the day, although we can’t see them.
- It is very rare that a meteorite will strike a human being. It’s more likely that it will fall into the ocean.
- The best time to view a meteor shower is in the early morning hours, preferably on a dark, moonless night.
- The earliest record of the Perseids meteor shower is found in Chinese annals from 36 AD.
The Andromeda Galaxy (M31) is the closest large galaxy to the Milky Way and is one only ten galaxies that can be seen unaided from the Earth. In approximately 4.5 billion years the Andromeda Galaxy and the Milky Way are expected to collide. It is accompanied by at least 10 satellite galaxies the most notable of which is the Triangulum Galaxy.
Galaxy Profile
- Type: Spiral
- Distance from Milky Way: 2.5 million light-years
- Diameter: 260,000 light-years
- Mass: 400 billion solar masses
- Number of Stars: 1 trillion
Facts About Andromeda
- While Andromeda is the largest galaxy in the Local Cluster it is not thought to be the most massive as the Milky May is thought to contain more dark matter making it the most massive
- The Andromeda Galaxy is approaching the Milky Way at approximately 100 to 140 kilometres per second
Earth Systems
Earth System Science – study of earth as a system, rather than separate studies of geology,
atmosphere science, chemistry.
Open System- most natural systems are open; both energy & matter flow into and out of
the system.
Closed System- energy moves in and out, but matter does not enter or leave.
Subsystems
-Hydrologic Cycle – connects hydrosphere, atmosphere, biosphere, geosphere.
-Rock Cycle – rock type changed to another rock type.
-Carbon Cycle – carbon moves through the 4 spheres
The area near the surface of the earth can be divided up into four inter-connected "geo-spheres:" the lithosphere, hydrosphere, biosphere, and atmosphere. Scientists can classify life and material on or near the surface of the earth to be in any of these four spheres.
The names of the four spheres are derived from the Greek words for stone (litho), air (atmo), water (hydro), and life (bio).
Hydrosphere – a dynamic mass of water.
-Ocean covers 71% of earth’s surface
-Ocean is 97% of earth’s water
Atmosphere – gaseous envelope.
-A relatively thin layer; 90% is within 10 miles of Earth’s surface.
- Protects us from Sun’s radiation
Biosphere – life on earth.
-Within a relatively narrow zone at or near the Earth’s surface.
Geosphere – solid earth.
-The largest of the Earth’s spheres.
The Earth's Atmosphere
The present atmosphere of the Earth is probably not its original atmosphere. Our current atmosphere is what chemists would call an oxidizing atmosphere, while the original atmosphere was what chemists would call a reducing atmosphere. In particular, it probably did not contain oxygen.
Composition of the Atmosphere
The original atmosphere may have been similar to the composition of the solar nebula and close to the present composition of the Gas Giant planets, though this depends on the details of how the planets condensed from the solar nebula. That atmosphere was lost to space, and replaced by compounds outgassed from the crust or (in some more recent theories) much of the atmosphere may have come instead from the impacts of comets and other planetesimals rich in volatile materials.The oxygen so characteristic of our atmosphere was almost all produced by plants (cyanobacteria or, more colloquially, blue-green algae). Thus, the present composition of the atmosphere is 79% nitrogen, 20% oxygen, and 1% other gases.
The atmosphere of the Earth may be divided into several distinct layers, as the following figure indicates.
The Troposphere
The troposphere is where all weather takes place; it is the region of rising and falling packets of air. The air pressure at the top of the troposphere is only 10% of that at sea level (0.1 atmospheres). There is a thin buffer zone between the troposphere and the next layer called the tropopause.
The Stratosphere and Ozone Layer
Above the troposphere is the stratosphere, where air flow is mostly horizontal. The thin ozone layer in the upper stratosphere has a high concentration of ozone, a particularly reactive form of oxygen. This layer is primarily responsible for absorbing the ultraviolet radiation from the Sun. The formation of this layer is a delicate matter, since only when oxygen is produced in the atmosphere can an ozone layer form and prevent an intense flux of ultraviolet radiation from reaching the surface, where it is quite hazardous to the evolution of life. There is considerable recent concern that manmade flourocarbon compounds may be depleting the ozone layer, with dire future consequences for life on the Earth.
The Mesosphere and Ionosphere
Above the stratosphere is the mesosphere and above that is the ionosphere (or thermosphere), where many atoms are ionized (have gained or lost electrons so they have a net electrical charge). The ionosphere is very thin, but it is where aurora take place, and is also responsible for absorbing the most energetic photons from the Sun, and for reflecting radio waves, thereby making long-distance radio communication possible.The structure of the ionosphere is strongly influenced by the charged particle wind from the Sun (solar wind), which is in turn governed by the level of Solar activity. One measure of the structure of the ionosphere is the free electron density, which is an indicator of the degree of ionization. Here are electron density contour maps of the ionosphere for months in 1957 to the present.
What is the HYDROSPHERE?
The hydrosphere is the liquid water component of the Earth. It includes the oceans, seas, lakes, ponds, rivers and streams. The hydrosphere covers about 70% of the surface of the Earth and is the home for many plants and animals.
(U.S. Fish and Wildlife Service/Craig Blacklock)
The hydrosphere, like the atmosphere, is always in motion. The motion of rivers and streams can be easily seen, while the motion of the water within lakes and ponds is less obvious. Some of the motion of the oceans and seas can be easily seen while the large scale motions that move water great distances such as between the tropics and poles or between continents are more difficult to see. These types of motions are in the form of currents that move the warm waters in the tropics toward the poles, and colder water from the polar regions toward the tropics. These currents exist on the surface of the ocean and at great depths in the ocean (up to about 4km).
(NOAA Photo Collection/Commander John Bortniak, NOAA Corps)
Large version | The characteristics of the ocean which affects its motion are its temperature and salinity. Warm water is less dense or lighter and therefore tends to move up toward the surface, while colder water is more dense or heavier and therefore tends to sink toward the bottom. Salty water is also more dense or heavier and thus tends to sink, while fresh or less salty water is less dense or lighter and thus tends to rise toward the surface. The combination of the water's temperature and salinity determines whether it rises to the surface, sinks to the bottom or stays at some intermediate depth. |
The oceans currents are also affected by the motion of the atmosphere, or winds, above it. The energy in the wind gets transferred to the ocean at the ocean surface affecting the motion of the water there. The effect of wind is largest at the ocean surface.
(NOAA Photo Collection/Harley Nygren, NOAA Corps)
Large version | The ocean serves two main purposes in the climate system. First, it is a large reservoir of chemicals that can contribute to the greenhouse effect in the atmosphere and energy absorbing 90% of the solar radiation which hits the surface. This reservoir changes very slowly limiting how fast the climate can change. Second, it works with the atmosphere to redistribute the energy received from the sun such that the heat in the topics, where a lot of energy is received from the sun, is transferred toward the poles, where heat is generally lost to space. |
(NOAA Photo Collection)
|
BIOSPHERE
The biosphere is simply the home of all known life that has ever existed in the entire universe.
Photograph by Rosanne Atencio Sevilla, MyShot
Biosphere 2
In 1991, a team of eight scientists moved into a huge, self-contained research facility called Biosphere 2 in Oracle, Arizona. Inside an enormous, greenhouse-like structure, Biosphere 2 created five distinct biomes and a working agricultural facility. Scientists planned to live in Biosphere 2 with little contact with the outside world. The experiments carried out in Biosphere 2 were designed to study the relationship between living things and their environmentand to see whether humans might be able to live in space one day.
The mission was supposed to last 100 years, with two teams of scientists spending 50 years each in the facility. Instead, two teams made it just four years, and the scientists moved out in 1994. Though the live-in phase is over, research is still taking place in Biosphere 2, with a main focus on global warming.
The
biosphere is made up of the parts of
Earth where life exists. The biosphere extends from the deepest
root systems of trees, to the dark environment of
ocean trenches, to
lush rain forests and high
mountaintops.
Scientists describe the Earth in terms of
spheres. The solid surface layer of the Earth is the
lithosphere. The
atmosphere is the layer of air that stretches above the lithosphere. The Earth’s water—on the surface, in the ground, and in the air—makes up the
hydrosphere.
Since life exists on the ground, in the air, and in the water, the biosphere overlaps all these spheres. Although the biosphere measures about 20 kilometers (12 miles) from top to bottom, almost all life exists between about 500 meters (1,640 feet) below the ocean’s surface to about 6 kilometers (3.75 miles) above sea level.
Origin of the Biosphere
The biosphere has existed for about 3.5 billion years. The biosphere’s earliest life-forms, called
prokaryotes, survived without
oxygen.
Ancient prokaryotes included single-celled organisms such as
bacteria and
archaea.
Some prokaryotes developed a unique chemical process. They were able to use sunlight to make simple
sugars and oxygen out of water and
carbon dioxide, a process called
photosynthesis. These photosynthetic organisms were so plentiful that they changed the biosphere. Over a long period of time, the atmosphere developed a mix of oxygen and other gases that could sustain new forms of life.
The addition of oxygen to the biosphere allowed more complex life-forms to evolve. Millions of different
plants and other photosynthetic species developed.
Animals, which
consume plants (and other animals)
evolved. Bacteria and other organisms evolved to
decompose, or break down, dead animals and plants.
The biosphere benefits from this
food web. The remains of dead plants and animals release
nutrients into the
soiland ocean. These nutrients are re-
absorbed by growing plants. This exchange of food and energy makes the biosphere a self-supporting and self-regulating system.
The biosphere is sometimes thought of as one large
ecosystem—a complex community of living and nonliving things
functioning as a single unit. More often, however, the biosphere is described as having many ecosystems.
Biosphere Reserves
People play an important part in maintaining the flow of energy in the biosphere. Sometimes, however, people
disrupt the flow. For example, in the atmosphere, oxygen levels
decrease and carbon dioxide levels increase when people clear
forests or burn
fossil fuels such as
coal and
oil.
Oil spills and
industrial wastes threaten life in the hydrosphere. The future of the biosphere will depend on how people interact with other living things within the zone of life.
In the early 1970s, the
United Nations established a project called
Man and the Biosphere Programme (MAB), which promotes
sustainable development. A network of biosphere reserves exists to
establish a working, balanced relationship between people and the natural world.
Currently, there are 563
biosphere reserves all over the world. The first biosphere reserve was established in Yangambi, Democratic Republic of Congo. Yangambi, in the
fertile Congo River Basin, has 32,000 species of trees and such
endemic species as forest elephants and red river hogs. The biosphere reserve at Yangambi supports activities such as
sustainable agriculture, hunting, and
mining.
One of the newest biosphere reserves is in Yayu, Ethiopia. The area is developed for
agriculture.
Crops such as honey, timber, and fruit are regularly
cultivated. However, Yayu’s most
profitable and valuable
resourceis an
indigenous species of plant,
Coffea arabica. This
shrub is the source of
coffee. Yayu has the largest source of wild
Coffea arabica in the world.
---------------------------------------------------------------------------------------------------------------------
LITHOSPHERE
Layers of the Earth
Here are the most main information you should know about the "layers", there are 4 layers in the earth, the crust, the massive mantle, outer core and the solid inner core. The Crust is the thinnest layer in the earth. The Mantle is very massive (huge) if you don't get huge imagine it takes up 80% of the earth now that is huge. The outer core is made of iron and nickel. The inner core is the most inner layer it is very solid. I bet you need more information if you do just scroll down and you'll find non-confusing information.
Crust
The crust is the most outer layer of the Earth. The crust is very rigid (Hard). The crust is made of granite and basalt. The ocean basically takes up 70% of the crust. The thin rocky crust is made out of silicon, aluminum, calcium, sodium and potassium. The crust is divided into continental plates that drift slowly every year (about a few centimeters). Just a few kilometers below your feet, its molten rock, extending to for thousands of kilometers down to the planet's super heated iron core. The entire earth's crust occupies just 1% of the earth's volume. The Earth's crust thickness is 30 km thick. The temperature of the crust is 2oo degrees Celsius (392 Fahrenheit) to 400 degrees Celsius (752 Fahrenheit).
Mantle
The Mantle is the second layer of the earth, it takes up 80% of the Earth. The mantle has two sections (Lithosphere and the
Asthenosphere). The temperature of the lithosphere and asthenosphere is 300 to 500 degrees celsius. The mantles temperature 4500 degrees celsius and made of 100% magma. In the mantle, convection currents occur. The convection currents occurs in the lithosphere and the asthenosphere. The mantle is very deep it is 1800- 2900 kilometers deep. A very interesting fact is that the mantle grows about a meter every year.
Lithosphere
The lithosphere is the upper part of the mantle. The Lithospheres temperature is about 400 degrees celsius. The lithosphere (lower mantle) is rigid part of the mantle. The lithosphere is not only part of the mantle it is the crust and the upper part of the mantle together. The depth of the lithosphere is 50-100 km thick.
Asthenosphere
The asthenosphere is the lower part of the mantle. The asthenosphere temperature is 300-500 degrees Celsius. The asthenosphere is ductile and can be pushed and deformed like silly putty in response to the warmth of the Earth. These rocks actually flow, moving in response to the stresses placed upon them by the motions of the deep interior of the Earth. The flowing asthenosphere carries the lithosphere of the Earth, including the continents, on its back.
Convection Currents
In the mantle are "convection currents" ,which make the mantle move. The lower mantle heats up and rises and cools down then gets pushed down because it is heavier. The currents keeps on going round and round. Convection currents occur because of density of a fluid is related to its temperature. Hot rocks lower in the mantle are less dense than their cooler counterparts below. The hot rock rises and the cooler rock sinks due to gravity.
Outer Core
The outer core is the third layer of the earth. The outer core surrounds the inner core. The outer core is the only liquid layer of the Earth. You could say that the outer core is basically a sea of iron and nickel. The outer core is 2100 miles and also is in an range of 200-300 kilometres thick. 7,200 to 9,000 degrees Fahrenheit (4,000 to 5,000 degrees Celsius).
Inner Core
The inner core is the most inner layer of the earth. The inner core contains iron, the iron in the inner core is not pure (so not just iron) scientists believe it contains sulfur and nickel and also smaller amount of other elements. The inner core is extremely hot it is somewhere between 9000 and 13000 degrees Fahrenheit (5000 and 7000 degrees Celsius).
Interior of the Earth: Crust, Mantle and Core, their composition based on Seismic evidences
Compositional Layers
The Earth is a sphere of radius 6371km which is stratified or layered. Compositional layers differ in chemical composition. The Earth has three compositional layers:
- The crust: low density silicate rock, 5-70 km thick. There are two distinct types of crust.
- Continental crust is variable in thickness and composition. Thickness ranges from 5-70 km. The composition ranges from mafic to felsic.
- Oceanic crust is uniform in thickness and composition. It is 5-6 km thick and is mafic in composition.
- The differences in thickness and density between continental and oceanic are responsible for the existence of ocean basins due to isostatic balance as the crust floats on the more dense mantle.
- The mantle: high density, ultramafic silicate rock which can flow when subjected to long duration stresses. The mantle is over 2900 km thick and makes up over 80% of the volume of the Earth. The mantle is not molten!
- The core: iron and nickel, liquid outer region with a solid center. The core is just over half the diameter of the Earth.
These compositional layers have sharp or abrupt boundaries between them.
Whole earth composition is estimated from unbiased samples of meteorites. Earth structure is obtained by combining this with seismic data.
Motion of liquid iron and nickel in the outer core gives the Earth a dipole magnetic field, nearly aligned with the rotational axis. The magnetic field of the Earth reverses spontaneously at random times. Over the last several million years, the average time between reversals has been about 200,000 years. The last reversal was 730,000 years ago. Reversals probably take less that 5,000 years. Reversals of the field probably involve a period of time where the field weakens substantially and becomes disorganized (non-dipole), then reorganizes in the opposite polarity. People should wear lead underwear during a reversal, as the Earth's surface will be bombarded with a higher than normal amount of cosmic radiation!
Mechanical Layers
In addition to the compositional layers, the Earth has mechanical layers. Mechanical layers differ in their strength or rigidity. These layers do not correspond on a one-to-one basis with the compositional layers. The Earth has five mechanic layers:
- The lithosphere is the outermost mechanical layer and is the most rigid layer of the Earth. The lithosphere consists of the crust, and some of the uppermost mantle. The lithosphere averages about 100 km thick. It is somewhat thicker beneath continents, and dramatically thinner under mid-ocean ridges.
- The asthenosphere lies beneath the lithosphere. It is a part of the mantle, approximately 100 km thick, with very little strength. The asthenosphere flows relatively easily and accomodates the movement of the overlying lithosphere. The upper and lower boundaries of the asthenosphere are diffuse as they involve gradual changes in the rigidity of the mantle, not a change in composition.
- The lower mantle or mesosphere consists of most of the mantle. This part of the mantle flows, but at much slower rates than the asthenosphere.
- The outer core is liquid iron (with some nickel and other elements). This is the only internal layer of the Earth that is a true liquid. The core-mantle boundary is the one mechanical boundary that is also a compositional boundary. Movement of the electically conductive fluid in the outer core generates the Earth's magnetic field.
- The inner core is solid. It has the same composition as the outer core, and is about half the diameter of the core.
EVIDENCES FOR THE COMPOSITION OF INTERIOR OF THE AERTH
 |
Introduction
Three centuries ago, the English scientist Isaac Newton calculated, from his studies of planets and the force of gravity, that the average density of the Earth is twice that of surface rocks and therefore that the Earth's interior must be composed of much denser material. Our knowledge of what's inside the Earth has improved immensely since Newton's time, but his estimate of the density remains essentially unchanged. Our current information comes from studies of the paths and characteristics of earthquake waves travelling through the Earth, as well as from laboratory experiments on surface minerals and rocks at high pressure and temperature. Other important data on the Earth's interior come from geological observation of surface rocks and studies of the Earth's motions in the Solar System, its gravity and magnetic fields, and the flow of heat from inside the Earth.
The planet Earth is made up of three main shells: the very thin, brittle crust, the mantle, and the core; the mantle and core are each divided into two parts. All parts are drawn to scale on the cover of this publication, and a table at the end lists the thicknesses of the parts. Although the core and mantle are about equal in thickness, the core actually forms only 15 percent of the Earth's volume, whereas the mantle occupies 84 percent. The crust makes up the remaining 1 percent. Our knowledge of the layering and chemical composition of the Earth is steadily being improved by earth scientists doing laboratory experiments on rocks at high pressure and analyzing earthquake records on computers. |
The Crust
Because the crust is accessible to us, its geology has been extensively studied, and therefore much more information is known about its structure and composition than about the structure and composition of the mantle and core. Within the crust, intricate patterns are created when rocks are redistributed and deposited in layers through the geologic processes of eruption and intrusion of lava, erosion, and consolidation of rock particles, and solidification and recrystallization of porous rock.
 Figure 1. The oceanic crust at the island of Hawaii is about 5 kilometers thick. The thickness of the continental crust under eastern California ranges from 25 kilometers under the Great Valley to 60 kilometers under the Sierra Nevada. |
By the large-scale process of plate tectonics, about twelve plates, which contain combinations of continents and ocean basins, have moved around on the Earth's surface through much of geologic time. The edges of the plates are marked by concentrations of earthquakes and volcanoes. Collisions of plates can produce mountains like the Himalayas, the tallest range in the world. The plates include the crust and part of the upper mantle, and they move over a hot, yielding upper mantle zone at very slow rates of a few centimeters per year, slower than the rate at which fingernails grow. The crust is much thinner under the oceans than under continents (see figure above).
The boundary between the crust and mantle is called the Mohorovicic discontinuity (or Moho); it is named in honor of the man who discovered it, the Croatian scientist Andrija Mohorovicic. No one has ever seen this boundary, but it can be detected by a sharp increase downward in the speed of earthquake waves there. The explanation for the increase at the Moho is presumed to be a change in rock types. Drill holes to penetrate the Moho have been proposed, and a Soviet hole on the Kola Peninsula has been drilled to a depth of 12 kilometers, but drilling expense increases enormously with depth, and Moho penetration is not likely very soon.
The Mantle
Our knowledge of the upper mantle, including the tectonic plates, is derived from analyses of earthquake waves (see figure for paths); heat flow, magnetic, and gravity studies; and laboratory experiments on rocks and minerals. Between 100 and 200 kilometers below the Earth's surface, the temperature of the rock is near the melting point; molten rock erupted by some volcanoes originates in this region of the mantle. This zone of extremely yielding rock has a slightly lower velocity of earthquake waves and is presumed to be the layer on which the tectonic plates ride. Below this low-velocity zone is a transition zone in the upper mantle; it contains two discontinuities caused by changes from less dense to more dense minerals. The chemical composition and crystal forms of these minerals have been identified by laboratory experiments at high pressure and temperature. The lower mantle, below the transition zone, is made up of relatively simple iron and magnesium silicate minerals, which change gradually with depth to very dense forms. Going from mantle to core, there is a marked decrease (about 30 percent) in earthquake wave velocity and a marked increase (about 30 percent) in density.
The Core
 Figure 2. Cross section of the whole Earth, showing the complexity of paths of earthquake waves. The paths curve because the different rock types found at different depths change the speed at which the waves travel. Solid lines marked P are compressional waves; dashed lines marked S are shear waves. S waves do not travel through the core but may be converted to compressional waves (marked K) on entering the core (PKP, SKS). Waves may be reflected at the surface (PP, PPP, SS). |
| The core was the first internal structural element to be identified. It was discovered in 1906 by R.D. Oldham, from his study of earthquake records, and it helped to explain Newton's calculation of the Earth's density. The outer core is presumed to be liquid because it does not transmit shear (S) waves and because the velocity of compressional (P) waves that pass through it is sharply reduced. The inner core is considered to be solid because of the behavior of P and S waves passing through it.Cross section of the whole Earth, showing the complexity of paths of earthquake waves. The paths curve because the different rock types found at different depths change the speed at which the waves travel. Solid lines marked P are compressional waves; dashed lines marked S are shear waves. S waves do not travel through the core but may be converted to compressional waves (marked K) on entering the core (PKP, SKS). Waves may be reflected at the surface (PP, PPP, SS).
Data from earthquake waves, rotations and inertia of the whole Earth, magnetic-field dynamo theory, and laboratory experiments on melting and alloying of iron all contribute to the identification of the composition of the inner and outer core. The core is presumed to be composed principally of iron, with about 10 percent alloy of oxygen or sulfur or nickel, or perhaps some combination of these three elements. |
 This table of depths, densities, and composition is derived mostly from information in a textbook by Don L. Anderson (see Suggested Reading). Scientists are continuing to refine the chemical and mineral composition of the Earth's interior by laboratory experiments, by using pressures 2 million times the pressure of the atmosphere at the surface and temperatures as high as 20000C.
SUMMARY
|
The Geologic Earth
Knowledge of the earth's interior has been gathered by three methods: by the analysis of earthquake waves passing through the earth (see seismology), by analogy with the composition of meteorites, and by consideration of the earth's size, shape, and density. Research by these methods indicates that the earth has a zoned interior, consisting of concentric shells differing from one another by size, chemical makeup, and density. The earth is undoubtedly much denser near the center than it is at the surface, because the average density of rocks near the surface is c.2.8 g/cc, while the average density of the entire earth is c.5.5 g/cc.
The Earth's Crust and the Moho
The outer shell, or crust, varies from 5 to 25 mi (8 to 40 km) in thickness, and consists of the continents and ocean basins at the surface. The continents are composed of rock types collectively called sial, a classification based on their densities and composition. Beneath the ocean basins and the sial of continents lie denser rock types called sima. The sial and sima together form the crust, beneath which lies a shell called the mantle. The boundary between the crust and the mantle is marked by a sharp alteration in the velocity of earthquake waves passing through that region. This boundary layer is called the Mohorovičić discontinuity, or Moho.
The Earth's Mantle
Extending to a depth of c.1,800 mi (2,900 km), the mantle probably consists of very dense (average c.3.9 g/cc) rock rich in iron and magnesium minerals. Although temperatures increase with depth, the melting point of the rock is not reached because the melting temperature is raised by the great confining pressure. At depths between c.60 mi and c.125 mi (100 and 200 km) in the mantle, a plastic zone, called the asthenosphere, is found to occur. Presumably the rocks in this region are very close to melting, and the zone represents a fundamental boundary between the moving crustal plates of the earth's surface and the interior regions. The molten magma that intrudes upward into crustal rocks or issues from a volcano in the form of lava may owe its origin to radioactive heating or to the relief of pressure in the lower crust and upper mantle caused by earthquake faulting of the overlying crustal rock. Similarly, it is thought that the heat energy released in the upper part of the mantle has broken the earth's crust into vast plates that slide around on the plastic zone, setting up stresses along the plate margins that result in the formation of folds and faults (see plate tectonics).
The Earth's Core
Thought to be composed mainly of iron and nickel, the dense (c.11.0 g/cc) core of the earth lies below the mantle. The abrupt disappearance of direct compressional earthquake waves, which cannot travel through liquids, at depths below c.1,800 mi (2,900 km) indicates that the outer 1,380 mi (2,200 km) of the core are molten. The inner 780 mi (1,260 km) of the core are solid, and the innermost 190 mi (300 km) of that may be almost pure iron. The outer core is thought to be the source of the earth's magnetic field: In the "dynamo theory" advanced by W. M. Elasser and E. Bullard, tidal energy or heat is converted to mechanical energy in the form of currents in the liquid core; this mechanical energy is then converted to electromagnetic energy, which we see as the magnetic field. The magnetic field undergoes periodic reversals of its polarity on a timescale that ranges from a few thousand years to 35 million years. The last reversal occurred some 780,000 years ago.
|
Origin of Earth: Nebular, Planetesimal, tidal, twin star & meteoritic hypothesis
The origin of the planets and their moons is a complex and as yet incompletely solved puzzle, although the basic outlines of the process are quite well understood. Most of our knowledge of the solar system's formative stages has emerged from studies of interstellar gas clouds, fallen meteorites, and Earth's Moon, as well as from the various planets observed with ground-based telescopes and planetary space probes. Ironically, studies of Earth itself do not help much because information about our planet's early stages eroded away long ago. Meteorites and comets provide perhaps the most useful information, for nearly all have preserved within them traces of solid and gaseous matter from the earliest times.
Despite the recent widely publicized discoveries of planets orbiting other stars (see Interlude 15-1), astronomers still have little detailed information on their properties, and so far there is no firm evidence for planets like Earth anywhere beyond our solar system. For that reason, our theories of planet formation still concentrate on the planetary system in which we live. Bear in mind, however, that no part of the scenario we will describe in the paragraphs that follow is in any way unique to our own system. The same basic processes could have occurred—and, many astronomers believe, probably did occur—during the formative stages of most of the stars in our galaxy. It is part of the job of the planetary scientist to distinguish between those properties of the solar system that are inherent—that is, that were imposed at formation—and those that must have evolved since the solar system formed. In this chapter we draw together all the planetary data we have amassed and show how the regularities—and the irregularities—of the solar system can be explained by a single comprehensive theory. |
MODEL REQUIREMENTS
 Any theory of the origin and architecture of our planetary system must adhere to the known facts. We know of nine outstanding properties of our solar system as a whole. They may be summarized as follows.
- Each planet is relatively isolated in space. The planets exist as independent bodies at progressively larger distances from the central Sun; they are not bunched together. In very rough terms, each planet tends to be twice as far from the Sun as its next inward neighbor.
- The orbits of the planets are nearly circular. In fact, with the exceptions of Mercury and Pluto, which we will argue are special cases, each planetary orbit closely describes a perfect circle.
- The orbits of the planets all lie in nearly the same plane. The planes swept out by the planets' orbits are accurately aligned to within a few degrees. Again, Mercury and Pluto are slight exceptions.
- The direction in which the planets orbit the Sun (counterclockwise as viewed from above Earth's North Pole) is the same as the direction in which the Sun's rotates on its axis. Virtually all the large-scale motions in the solar system (other than comet orbits) are in the same plane and in the same sense. The plane is that of the Sun's equator, and the sense is that of the Sun's rotation.
- The direction in which most planets rotate on their axis is roughly the same as the direction in which the Sun rotates on its axis. This property is less general than the one just described for revolution, as three planets—Venus, Uranus, and Pluto—do not share it.
- Most of the known moons revolve about their parent planets in the same direction that the planets rotate on their axes.
- Our planetary system is highly differentiated. The inner terrestrial planets are characterized by high densities, moderate atmospheres, slow rotation rates, and few or no moons. By contrast, the jovian planets, farther from the Sun, have low densities, thick atmospheres, rapid rotation rates, and many moons.
- The asteroids are very old and exhibit a range of properties not characteristic of either the inner or the outer planets or their moons. The asteroid belt shares, in rough terms, the bulk orbital properties of the planets. However, it appears to be made of primitive, unevolved material, and the meteorites that strike Earth are the oldest rocks known.
- The comets are primitive, icy fragments that do not orbit in the ecliptic plane and reside primarily at large distances from the Sun.
All these observed facts, taken together, strongly suggest a high degree of order within our solar system. The whole system is not a random assortment of objects spinning or orbiting this way or that. Consequently, it hardly seems possible that our solar system could have formed by the slow accumulation of already-made interstellar "planets" casually captured by our Sun over the course of billions of years. The overall architecture of our solar system is too neat, and the ages of its members too uniform, to be the result of random chaotic events. The overall organization points toward a single formation, an ancient but one-time event, 4.6 billion years ago. A convincing theory that explains all the nine features just listed has been a goal of astronomers for many centuries. |
ADDITIONAL CONSIDERATIONS
It is equally important to recognize what our theory of the solar system does not have to explain. There is plenty of scope for planets to evolve after their formation, so circumstances that have developed since the initial state of the solar system was established need not be included in our list. Examples are Mercury's 3:2 spin—orbit coupling, Venus's runaway greenhouse effect, the Moon's synchronous rotation, the emergence of life on Earth and its absence on Mars, the Kirkwood gaps in the asteroid belt, and the rings and atmospheric appearance of the jovian planets. There are many more. Indeed, all the properties of the planets for which we have already provided an evolutionary explanation need not be included as items that our theory must account for at the outset.
In addition to its many regularities, our solar system also has many notable irregularities, some of which we have already mentioned. Far from threatening our theory, however, these irregularities are important facts for us to consider in shaping our explanations. For example, it is necessary that the explanation for the solar system not insist that all planets rotate in the same sense or have only prograde moons, because that is not what we observe. Instead, the theory of the solar system should provide strong reasons for the observed planetary characteristics yet be flexible enough to allow for and explain the deviations, too. And, of course, the existence of the asteroids and comets that tell us so much about our past must be an integral part of the picture. That's quite a tall order, yet many researchers now believe that we are close to that level of understanding.
|
FUNDAMENTAL IRREGULARITIES:
1.Sizes and Scales
There are many popular misconceptions concerning the size and scale of objects in the Solar System. These mostly have to do with a failure to realize the relative radii of planets and the Sun, and the failure to appreciate how large the outer solar system is relative to the inner solar system.
The Relative Radii of the Sun and Planets
The Sun and the gas giant planets like Jupiter are by far the largest objects in the Solar System. The other planets are small specks on this scale, as the following figure illustrates.
Indeed, on this scale the smaller planets like Pluto and Mercury are barely visible.
Masses and Densities
The masses of the planets are also concentrated in the Gas Giant planets Jupiter, Saturn, Uranus, and Neptune, as the following graph indicates.
However, the large mass of these planets comes from their absolute sizes, not their densities. The inner planets are by far the most dense, as the following graph indicates:
This distribution of masses and densities in the Solar System is a key observation that a theory of the origin of the Solar System must explain.
Here is an astrophysical calculator that will display basic astronomical constants and solar system data at the touch of a button, and also allow calculations using these quantities.
2.Revolution and Rotation
of the Planets
As discovered by Kepler, the planets orbit on ellipses with the Sun at one focus. In addition, the planets all revolve in the same direction on their orbits (direct orbital motion). Let's now consider the orbits of the planets in more detail.
The Inner Solar System
Here is the inner solar system constructed with the Solar System Live software.
The sizes and shapes of the orbits are realistic, as is the relative positions of the planets for the date in the Fall, 1996, when the plot was constructed. The sizes of the planetary symbols are not to scale; the planets would be too small to see at this scale as more than dots of light. Notice the eccentricity of the orbits for Mercury and, to a lesser degree, Mars. From this perspective (which corresponds to looking down on the Northern hemisphere of the Earth), the planets all revolve in a counter-clockwise sense, as indicated by the arrow.
Here are the present positions (to scale) of planets in the inner solar system. In this plot, the portion of orbit in blue is above and the portion in green is below the plane of the ecliptic. As noted in conjunction with Kepler's Third Law, motion of the innermost planets is much faster than that of the outermost; this animation illustrates realistic motion of the inner solar system.
The preceding views represent a "top" or North perspective. Here is a side perspective of the inner Solar System showing the tilt of the planetary orbits with respect to the plane of the ecliptic.
In this figure the white portion of the orbit is above the ecliptic plane and the yellow portion is below. Notice that the orbits of the inner planets are nearly, but not quite, in the same plane. The orbit of Mercury, in addition to being the most eccentric, has the largest tilt (7 degrees) with respect to the ecliptic plane.
The Entire Solar System
Here is the entire Solar System to scale for the orbits, also in the Fall, 1996:
Notice the enormous amount of empty space in the outer Solar System. To show the entire Solar System to scale, the inner Solar System becomes so compressed that the planet orbits almost appear to run together. The very large eccentricity of Pluto's orbit is also obvious.
Here are the present positions (top view, to scale) of all planets in the Solar System. As above, the portion of orbit in blue is above the plane of the ecliptic; portion in green is below the plane of the ecliptic.
The following figure shows the full Solar System to scale from a side view to illustrate the tilt of the orbits.
3.Conservation of Angular
Momentum
Our theory for the origin of the Solar System is a very old one with some modern innovations called the Nebular Hypothesis. A crucial ingredient in the nebular hypothesis is the conservation of angular momentum.
Angular Momentum
Objects executing motion around a point possess a quantity called angular momentum. This is an important physical quantity because all experimental evidence indicates that angular momentum is rigorously conserved in our Universe: it can be transferred, but it cannot be created or destroyed. For the simple case of a small mass executing uniform circular motion around a much larger mass (so that we can neglect the effect of the center of mass) the amount of angular momentum takes a simple form. As the adjacent figure illustrates the magnitude of the angular momentum in this case is L = mvr, where L is the angular momentum, m is the mass of the small object, v is the magnitude of its velocity, and r is the separation between the objects.
Ice Skaters and Angular Momentum
This formula indicates one important physical consequence of angular momentum: because the above formula can be rearranged to give v = L/(mr) and L is a constant for an isolated system, the velocity v and the separation r are inversely correlated. Thus, conservation of angular momentum demands that a decrease in the separation r be accompanied by an increase in the velocity v, and vice versa. This important concept carries over to more complicated systems: generally, for rotating bodies, if their radii decrease they must spin faster in order to conserve angular momentum. This concept is familiar intuitively to the ice skater who spins faster when the arms are drawn in, and slower when the arms are extended; although most ice skaters don't think about it explictly, this method of spin control is nothing but an invocation of the law of angular momentum conservation.
