The Earth

The Earth

Shape and Size of the Earth

The Earth is an oblate spheroid, bulges at the equator and is flattened at the poles. For such shape, the Earth is called as geoid. Geodesy is a branch of science that deals with measuring the Earth’s size and shape. 

Due to rotation of Earth, centrifugal force is generated which is greatest at the equator that causes a slight outward bulge there, so the equatorial circumference is larger than polar circumference. 

Gravitational pull is strongest at the flattened poles and gradually weaken towards the equator. So, our weight is lowest at the equator and highest at the pole. Earth is the third nearest planet to the Sun and in size, it is the fifth largest planet and largest among the 4 inner planets. 

The equatorial circumference is 83 miles more than polar circumference and equatorial diameter is 26 miles (~ 42 km) greater than its polar diameter. — The spherical shape of the Earth is also marked by the intervening highlands and oceans on its surface. 

The surface area of the Earth is approximate 510 million km2 among which water is 361 million km2 (70.8%) and land is about 149 million km2. Water is more concentrated in Southern hemisphere and the landmass is more concentrated in Northern hemisphere of the Earth considering equator as the boundary line. 

Of all the planets in our solar system, the Earth has the greatest density approximately 5.52 grams cm3, second in line is Mercury.  

There is an antipodal arrangement of land and water on directly opposite side of the Earth, means land is opposite to water and vice-versa on the globe.  

Even, the North Arctic ocean is opposite to the Antarctic landmass. Only a few landmass has antipodal to landmass, such pairs are like New Zealand-Spain, Bermuda-Perth, Jakarta-Bogota, China-Argentina, Lima-Bankok etc. 

Antipodal points on Earth of a location can be calculated by converting North latitude to South latitude and subtracting longitude value from 180° and reversing East to West or vice-versa.

Facts about Earth 

◆ Mass 5.97 1024 × kg 

◆ Equatorial Diameter 12756 km 

◆ Polar Diameter 12714 km 

◆ Equatorial Circumference 40030 km 

◆ Known Satellites 1, the Moon 

◆ Orbit Distance 149598262 km (1 AU) 

◆ Orbit Period 365.26 Earth days 

◆ Surface Temperature -88°C to 58°C 

◆ Average Atmospheric Temperature 14.2°C 

◆ Earth’s Atmosphere 

Nitrogen (78%), 

Oxygen (21%), 

Argon (0.93%) 

and Carbon dioxide (0.03%) 

◆ Earth’s Orbital Speed 29.8 km/sec 

◆ Density 5.52 g/cm3

Measurement of Earth’s Age 

Several methods to determine the age of the Earth are: 


Scientific observation shows that erosion takes place at about 1 ft in every 5000 years. Knowing this method, we can estimate the age of rock formations like the Grand Canyon.


Another method used is to measure the rate at which sediment is deposited. Scientists think it takes between 500 and 10000 years to deposit 1 foot of sediment. This method is not as accurate as the erosion method. 

Salinity of the Oceans 

Some geologists try to measure the age of the Earth by the amount of salt in the ocean. 

First, they need to find out how much salt is in the oceans. Then, they find out how much salt rivers pour into the oceans each year. 

By comparing how much salt there is in the oceans now to how much is carried in by rivers each year, scientists can estimate the age of the oceans. 

Radioactive Method 

It is the method to study the uranium in igneous and metamorphic rocks. Uranium is a mildly radioactive substance that breaks down very slowly to form other elements and eventually into lead and cannot be influenced by temperature and pressure. 

Scientists calculate that it takes about 5 billion years for a half of a piece of uranium to become lead. By looking at different rocks and comparing the amount of uranium still in the rock to the amount of lead that has been formed, they have measured the age of the Earth about 4.5 billion years. 

Carbon-14 Dating 

All organic life forms have some amount of carbon-14 in them. When they die, no more carbon-14 is produced, but instead the carbon-14 begins to slowly break down. Scientists think it takes 5600 years for half of a piece of carbon-14 to break down. 

The fossil remains of creatures that had carbon-14 in them are found in sedimentary rock. By comparing the amount of carbon-14 in a rock to the amount of other substances that have been formed, as a result of the breaking down of the carbon-14, scientists can date the rock. 

Carbon-14 dating is used to find the age of rocks upto 15000 years old and the radioactive method is used for older rocks. 

Motions of the Earth 

As a celestial body, Earth has different varieties of spatial motions. It may include rotation, revolution, axial precession, change in tiltation of axis, changes in the ellipticity of the orbit (spin motion). 


Rotation is the motion of the Earth along its axis, around the imaginary line passes through North pole and South pole. Earth rotates from West to East i.e. anti-clockwise. So, Sun, Moon and other stars rises in the East and set on the West. 

Rotational motion causes day and night, so, called daily motion. Speed of the rotation decreases from equator to poleward i.e. the speed is about 1670 km/h at equator and about 1120 km/h at 45° latitude. 

Solar Day

It is found when the duration of Earth’s revolution around the Sun is calculated in terms of days, while taking Sun as stationary. Duration of a solar day is exactly 24 hours. It is the average interval between two successive midnights. It is also called synodic day. 

Sideral Day 

The duration between the passage of a particular star over a meridian twice is called sideral day. Its duration is of about 23 hours and 56 minutes. It is smaller than Solar day. 

Rotation causes deflation of ocean currents and winds differently in different hemisphere, popularly known as coriolis force. It also causes alternate rise and fall in ocean waves twice daily. Rotation of Earth creates a centrifugal force that causes a bulge at the equator and reduces the gravitational pull there. 


Revolution is the motion of the Earth on its elliptical orbit around the Sun. Earth revolves at about 18.5 miles per second or 29.6 km per second. It is responsible for experience of seasons on Earth. One complete revolution is called a year and can be called synodic/solar year/tropical year or sideral year as per the relative calculation.  

The sideral year is defined to be the time for the Sun to return to the same position with respect to the stars. Whereas, the tropical year is the time for the Sun to return to the same position relative to the Earth’s axis, which is normally calculated from one vernal equinox (summer solstice) to another. The solar year is shorter than the sideral year by about 20 minutes and 23 seconds because of the precession. 

Hipparchus was the first man to take exact observations of the length of the year and later Ptolemy also made the similar one. 

The average distance between Earth and Sun is approximately 93 million miles or 150 million km, but it varies as the orbit of Earth is elliptical not circular. 

The position at which Earth is closest to the Sun is called perihelion (about 147 million km) likely occur about 3rd January, every year. Similarly, the farthest position of the Earth from the Sun is called apehelion, likely occur about 4th July every year (152 million km). 

Axial Precession 

The rotational axis of the Earth is tilted with respect to the normal to the plane of the ecliptic, presently at an angle of about 23.5°. Because of the oblate shape of the Earth and the tilt, the Sun exerts a gravitational pull that differs in force at the two poles. The effect is to attempt to set the Earth up straight i.e. to try to right the axis to be normal to the ecliptic. 

However, instead of straightening, the Earth’s rotation axis precesses, i.e. it exhibits a slow, conical motion around the orbital axis. Infact, the ‘righting force’ has the effect of causing the rotational axis to execute a circular, wobbling motion, like a spinning top. The precession of the equinoxes is responsible for the difference between the Julian and Gregorian calendars.

Changes in Tilt 

While the inclination of the Earth’s rotational axis is presently 23.5°, it has moved a little in the past. Like the precession of the equinoxes that reflects the circular motion of the rotational axis, the tilt changes periodically also from about 24.5° to 21.5° over a period of about 40000 years. So, as the rotational axis wobbles, it also tilts back and forth. 

This motion provides no insight into the Earth’s internal properties, but it turns out to be very important as an influence on the Earth’s climatic changes. 

Changes in the Earth’s Orbit 

The Earth revolves around the Sun in an elliptical orbit every 365 days with the Sun at one focus. This orbital state too is not static. The ellipticity of the orbit, changes, also in a periodic way, with this period being the longest at around 100000 years, the ellipticity changes from 0.01 to 0.007. 

In summary, these three motions can be thought of as a 100000 years stretch of the orbital ellipse, a 40000 years tilt of the rotational axis, together with a 26000 years wobble of the rotational axis. Wobble and stretch are actually coupled, if one changes the other is also forced to change alongwith it. 


The imaginary surface on which Earth orbits around the Sun is called as the plane of the ecliptic. The Earth’s axis is inclined at 66.5° to the plane of the ecliptic (or 23.5° from the perpendicular to the plane of the ecliptic). The Earth maintains its orientation with respect to the stars. Thus, the North pole points in the same direction to Polaris, the North star, as it revolves around the Sun. Consequently, the Northern hemisphere tilts away from the Sun during one-half of Earth’s orbit and towards the Sun through the other half. 

If the Earth would not have been tilted on its axis, the days and nights would have been of same duration, always. Moreover, if the Earth would not have been revolving around the Sun, one of the hemispheres would have long days and short nights, whereas the other one would have short days and long nights. 

The Earth moves not only on its axis, but also in its orbit around the Sun. Therefore, the Earth changes its position continuously with respect to the Sun. There are four major positions of the Earth, while it revolves around the Sun and these positions bring different seasons on the Earth: 

(i) Position on 21st June In this position, the Sun shines perpendicularly over the Tropic of Cancer. This position is called the summer solstice. Infact, from 21st March, the Sun starts shifting towards the North, gradually. It is the time of summer season in the Northern hemisphere, while in the Southern hemisphere, it is winter season. The day in the Northern hemisphere is longest on 21st June. From 21st June, the Sun starts retreating towards the equator and hence, the heat of summer gradually decreases. On this date Sun does not set below the horizon at the arctic circle.

(ii) Position on 22nd December In this position, the Sun shines perpendicularly over the Tropic of Capricorn. This position is called winter solstice. During this period, days are long and nights are short in the Southern hemisphere and vice-versa in Northern hemisphere.

(iii) Position on 21st March The Sun starts shifting towards North gradually from 21st March. This position marks the summer in the Northern hemisphere and winter in the Southern hemisphere. On this day, the Sun also shines directly overhead the equator. It is called spring equinox

(iv) Position on 23rd September The Sun shines directly overhead the equator. Therefore, half part of all latitudes receives the sunlight at these times. Hence, everywhere the duration of the day and night is equal. Seasons are also similar in both the hemispheres. It is called autumn equinox. 

Effects of Earth’s Motion 

Alongwith creating day-night and seasons, the motions also create spatial temperature variations on the Earth.  

Sun oscillates overhead regions within the tropics. Sunlight is concentrated time-to-time over these regions, but it becomes gradually oblique and faint towards the poles. So, tropical regions are net gainers of heat during respective summer seasons and beyond these regions are permanent net looser of heat on Earth. Whereas the equatorial region is always net gainer of heat on Earth. 


The points at which the rotational axis intersects the Earth’s surface are called North pole and South pole. Latitude which divides the Earth into two equal halves is called equator. Its value is 0°. The position of all the latitudes is either to North or to South of the equator. The Northern half of the Earth from the equator is known as the Northern hemisphere and the Southern half is known as the Southern hemisphere. 

The latitude of a place is the angular distance of a place North or South of the equator, as measured in degrees from the center of the Earth. 

The line of latitude are drawn parallel to the equator in circles, so called parallels and grow smaller towards the poles. Thus, latitude of the great circle or equator is the largest and nearly a point at the poles. 

Total number of latitudes are 181 and the most important lines of latitude are the Equator (0°), the Tropic of Cancer (23 1/2° N)  , the Tropic of Capricorn (23 1/2° S), the Arctic Circle (66 1/2°) N and the Antarctic Circle (66 1/2°) S, North Pole (90° N) and South Pole (90° S). 

The average latitudinal distance of 1° is about 69 miles or 111 km. As the Earth is slightly flattened at the poles, the linear distance of a degree of latitude at the pole is little longer than that at the equator. 

During the winter and summer solstices, the area on the Earth between the Arctic circle (at 66.5° N latitude) and the North pole has 24 hours of darkness and daylight, respectively.  

The same phenomena occurs for the area between the Antarctic circle (at 66.5° S latitude) and the South pole, except that the seasons are reversed in the Southern hemisphere. At the poles, the Sun is below the horizon for 6 months of the year.  

For those living outside, the tropics (poleward of 23.5° North and South latitude), the noon Sun will never shine directly overhead. 


Since, the equator is a circle, it can be divided into 360 divisions and the imaginary line joining both the poles passing through such divisional points on the equator are like semi-circles and called meridians

Unlike the equator, which is centrally placed between the poles, any meridian could have been taken to begin the numbering. It was finally decided in 1884, to choose as the zero meridian, the one which passes through the Royal Astronomical Observatory at Greenwich, near London.  

This is the Prime Meridian (0°) from which all other meridians radiate Eastwards and Westwards upto 180°. 

Less conventionally, the part of the Earth on the Eastern side of the Prime Meridian is called Eastern hemisphere and that on the Western side of it is called Western hemisphere. 

These meridians shows the longitude of a place on the globe at its angular distance, East or West of the Prime Meridian. 

The Prime Meridian and the 180° longitude that lies just opposite to the Prime Meridian together form one complete circle. From Prime Meridian, Eastward longitudes are marked as ‘E’ upto 179°E and Westward longitudes are marked as ‘W’ upto 179°W, but 180° is left unlabelled. So, there are total 360 longitudes.  

Like latitudes, longitudes also can be sub-divided into minutes (′) or seconds (′′) for precise locational analysis. As the parallels of latitude become shorter polewards, so the meridians of longitude which converge at the poles, enclose a narrower space. The degree of longitude therefore decrease in length towards pole. For this reason, they are not used for calculating distances. 

Great Circles and Small Circles 

A great circle is a circle, which divides the Earth into two equal parts or hemispheres.  

A great circle is the longest circle that can be drawn on the globe. Conversely, a circle on the surface of the Earth, that does not pass through the center of the Earth and thus, divides the Earth into two unequal parts is called a small circle. 

Among the parallels of latitude, only the equator is a great circle and all other parallels are small circles. However, among the meridians of longitude, all are semi-circles and form great circle alongwith meridian running opposite side. Apparently, an infinite number of great circles can be drawn on the surface of Earth. Important Facts on Longitude and Latitudes 

The Equator passes through 13 countries: Ecuador, Colombia, Brazil, Sao Tome and Principe, Gabon and Republic of the Congo, Democratic Republic of the Congo, Uganda, Kenya, Somalia, Maldives, Indonesia and Kiribati. Among physical features, the equator passes through Andes, Mouth of Amazon, Congo basin, Lake Victoria, Mouth of R Juba (Somalia), Sumatra, Borneo. 

The Tropic of Cancer at 23½° N runs through Mexico, Egypt, Saudi Arabia, India, Bangladesh, Myanmar, South China and Taiwan. Among physical features, it passes through Gulf of Mexico, Mexican plateau, Saharan desert, river Nile, Red sea, Arabian peninsula, Arabian sea,

Ganga-Brahmaputra-Meghna confluence, Indo-China peninsula and Red river in China.

Tropic of Capricorn at 23½ S runs through Chile, Northern Argentina, Paraguay, Southern Brazil, Botswana, Northern South Africa, Madagascar, Australia etc among major countries. Among major physical features, it passes through Andes, Granchaco, Brazilian highlands, Namib desert, Kalahari desert, Mozambia channel, Great Dividing range etc. 

Antarctic Circle (66½ N) passes through entirely over ocean except some part of Antarctica 

Arctic circle (66½ N) passes through Bejing strait, Alaska, Davis strait, Greenland, Scandinavia and Siberian plateau. 

Prime Meridian passes through United Kingdom, Paris, Spain, Algeria, Mali, Ghana etc. 

Distribution of Date and Time  

To eliminate the confusion of time and date at local and international level, the world is divided into standard time belts. Prime Meridian is used as the basis for reckoning of international time, which is the reference of local time or noon of Greenwich Meridian. 

Earth rotates from West to East, hence, places situated in the East of Prime 

Meridian experience Sun rise earlier than the places in the West.  

Earth takes 24 hours for one complete rotation of 360°, it implies the Sun appears to move at the rate of 15° in 1 hour or 1° in 4 minutes. Sun is overhead each meridian after 4 minutes, such position can be taken for calculation of local time. 

Taking Greenwich Meridian as standard time zone (GMT), the whole world has been divided into 24 standard time zones, each of which differs from the next by 15° in longitude or 1 hour in time. 

Every 15° we go Eastwards, local time is advanced by 1 hour and conversely if we go Westward, local time is retarded by 1 hour. Places East of Prime Meridian see the Sun earlier and gain time, whereas places West of it see the Sun later and lose time. A simple memory technique may be East Gain Add (EGA) and West Lose Subtract (WLS) for finding the local time of a region if GMT is known. 

Indian Government has accepted the meridian of 82 1/2 E for the standard time, which is 5 hours 30 minutes ahead of GMT. Nepal and Sri Lanka also follow the same standard time. 

Some larger countries adopt several time zones for practical purposes i.e. Russia has 11 time zones, USA and Canada has 5 time zones, Australia has 3 time zones, but China has only 1 time zone. International Date Line (IDL) 

The Prime Meridian also helps in establishment of the International Date Line, which is congruent with 180° longitude. 

When we count the time of the 180° longitude from Eastern side of GMT, it will be 12 hours ahead and when it is counted Westward, it is 12 hours behind the GMT. That means, difference of 24 hours or a complete day occur on the either side of the meridian. When the longitude is crossed from one side to another, the date is changed exactly 1 day. So, it is called International Date Line. 

A traveller crossing the date line from East to West losses a day (the time he made) and gains a day when travels West to East (the gain of time he encountered). 

180° meridian was chosen as IDL because it passes through the middle of Pacific ocean and there is practically no landmass and wherever there is landmass, a deviation has been taken to avoid confusion of time and date. 

Samoa was previously located East of the IDL, but in 2011 it moved the IDL to the East of the country, so that Samoa would lie to the West of the date line for better trading with its neighbours. 

The IDL curves 8 times from the normal 180° meridian at Bering strait, Fiji, Tonga and other islands to prevent confusion of day and date. Some of them keep Asiatic or New Zealand standard time, others follow the American date and time. 

Daylight Saving Time (DST) 

In summer time in several countries, there is a practice of advancing clocks, so that, evenings have more daylight and mornings have less. Typically, clocks are adjusted forward 1 hour near the start of spring and are adjusted backward in autumn. Although, an early goal of DST was to reduce evening usage of incandescent lighting, formerly a primary use of electricity, modern heating and cooling usage patterns differ greatly. Daylight Saving Time begins in the Northern hemisphere between March-April and ends between September-November. Daylight Saving Time begins in the Southern hemisphere between September-November and ends between March-April. 

The Earth and the Moon 

The Moon has size about 27% of the Earth. Its diameter is about 3474 km in comparison to Earth’s 12742 km. The surface area of Moon is 37.9 million km2 and that is about only 7.4% of Earth and less than Asia. The volume of Moon is only 2% of Earth’s volume and mass of the Moon is only 1.2% of the mass of the Earth. 

The Moon orbits the Earth in an elliptical path and the closest position of Moon to Earth is called perigee and the farthest distance is called the apogee. Its average distance from the Earth is about 3.844 105 × km or 0.00243 AU. 

Highest point on the Moon’s surface is Mount Leibnitz (35000 ft) situated on the South pole of the Moon. Moon’s orbital velocity is about 3680.5 km/h or 1.02 km/sec. Its orbital eccentricity is about 0.0554 and orbital inclination is about 5.16°. Its density is about 3.344 g/ cm3 (about 0.607 of Earth) and surface gravity is about 1 8 th of Earth, so has lower escape velocity of about 2.376 km/sec (about 0.2% of Earth). 

Moon’s sideral rotation period is synchronous with its orbital period and about 27.322 Earth days, so observers on Earth only see one side of the Moon. Phases of the Moon 

The changing angles between Earth, the Sun and the Moon determine how much of the Moon’s illuminated surface can be seen from Earth and cause the phases of the Moon. As the Moon orbits the Sun and we see different amounts of its sunlit side, its shape seems to change, which is called phases of the Moon. 

Phases of Moon starts from the New Moon every month when Moon does not look at all because the complete dark past of the Moon faces the Earth. Then only a small part of the Moon is seen bright which is called (recent and it gradually becomes half Moon when half of the Moon lit, then when the increasing brighter portion match upto 3/4th of the Moon it is called Gibbous and then it converted to full Moon.) 

After Full Moon or the complete brightness, the Moon lit starts receeding through the stages of gibbous, half Moon, Crescent and finally becomes invisible as new Moon. 

Nearly, 59% of the Moon’s surface permanently seen from the Earth as its rotational period is synchronous with its orbital period. Such surface is called the near side of the Moon whereas other 41% are called the far side of the Moon. Moon’s apparent size in our sky varies by 13% as its distance from Earth varies.


An eclipse is a complete or partial obscuration of light from a celestial body as it passes through the shadow of another celestial body. 

Solar eclipse occurs near the New Moon position, when the Moon is between the Sun and Earth, thus, obscuring a part of whole of the Sun as viewed from the Earth.  

Lunar eclipse occurs near the Full Moon position, when the Earth is between the Sun and the Moon and Earth’s shadow obscure the Moon as viewed from the Earth. 

Moon’s orbital plane inclined 5° to the orbital plane of the Earth, so eclipses do not occur every Full Moon or New Moon positions. 

Syzygy is the position of alignment when Earth comes in between Sun and Moon on a straight line; in such position, lunar eclipse occurs and conjunction is the position when Sun and Moon lie on one side of the Earth and then solar eclipse occurs. 

The portion of the Sun or Moon covered by the vertical shadow of any celestial body like Earth or Moon is called Umbra and it is deep dark whereas the faint shadow region is called Penumbra

During a total eclipse, as the Moon’s shadow is short enough to cover the whole of the Sun then the outer region of the Sun still glow and looks bright as a ring as observed from the Earth. Such phenomena is called diamond ring

Unlike a solar eclipse, which can only be viewed from a certain relatively small area of the world, a lunar eclipse may be viewed from anywhere on the night side of the Earth. 

A lunar eclipse lasts for a few hours, whereas a total solar eclipse lasts for only a few minutes at any given place, due to the smaller size of the Moon’s shadow. 

Lunar eclipses are more frequent than solar eclipses. 

The Earth’s Magnetic Field  

The Earth has a substantial magnetic field quite similar to a simple bar magnet. The axis of the magnetic field is tipped with respect to the rotation axis of the Earth. The axis of Earth’s magnet and the geographical axis do not coincide. The axis of the Earth’s magnetic field is inclined at an angle of about 111 2 ° with the geographical axis. Thus, true North (defined by the direction to the North rotational pole) does not coincide with magnetic North (defined by the direction to the North magnetic pole). — The South pole of the Earth’s magnet is in the geographical North because it attracts the North pole of the suspended magnet and vice-versa. Thus, there is a magnetic S-pole near the geographical North and a magnetic N-pole near the geographical South. The positions of the Earth’s magnetic poles are not well defined on the globe; they are spread over an area. The magnetic field is strongest near the magnetic poles and is weakest near the equator. 

The magnetic poles of the Earth are defined as the location of the strongest vertical magnetic field. This places the magnetic North pole just West of Northern Greenland (about N80° W70°) and the magnetic South pole near the coast of Antarctica South of Australia (about S75° E150°). The magnetic equator does not circle the Earth as a smooth line like the geographic equator, but instead it meanders North and South.  

The magnetic field lines usually dip towards or come out of the Earth’s surface at some angle. This angle is called the magnetic inclination or the magnetic dip at that place. At the magnetic poles, the angle of dip is 90°. 

The line on the Earth’s surface passing through the places having angle of dip 0° is called the magnetic equator, it passes through Thumba in South India, where the space research centre is located.

Origin of the Magnetic Field 

Magnetic fields are produced by the motion of electrical charges. The origin of the Earth’s magnetic field is not completely understood, but is thought to be associated with electrical currents produced by the coupling of convective effects and rotation in the spinning liquid metallic outer core of iron and nickel. This mechanism is termed the dynamo effect, but it is not constant in direction. 

Rocks that are formed from the molten state contain indicators of the magnetic field at the time of their solidification.  

The study of such ‘magnetic fossils’ indicates that the Earth’s magnetic field reverses itself every million years or so the North and South magnetic poles switch. 

The Earth’s Magnetosphere 

The solar wind is a stream of ionised gases that blows outward from the Sun at about 400 km/sec and that varies in intensity with the amount of surface activity on the Sun. The Earth’s magnetic field shields it from much of the solar wind. When the solar wind encounters Earth’s magnetic field, it is deflected like water around the bow of a ship. 

The imaginary surface at which the solar wind is first deflected is called the bow shock. The corresponding region of space lying behind the bow shock and surrounding the Earth is termed the magnetosphere. It represents a region of space dominated by the Earth’s magnetic field in the sense that it largely prevents the solar wind from entering. However, some high energy charged particles from the solar wind leak into the magnetosphere and are the source of the charged particles trapped in the Van Allen belts

Van Allen Radiation Belts  

A fundamental property of magnetic fields is that they exert forces on moving electrical charges. Thus, a magnetic field can trap charged particles such as electrons and protons as they are forced to execute a spiraling motion back and forth along the field lines. It was discovery in the late 1950s that the Earth is surrounded by two regions of particularly high concentration of charged particles called the Van Allen Radiation belts. 

The radiation belt has inner and outer belts. The primary source of these charged particles is the stream of particles emanating from the Sun known as solar wind. The charged particles trapped in the Earth’s magnetic field are responsible for the aurora (Northern and Southern lights). 

The belts are extending from 650 km to 65000 km above the Earth. The inner belt is mainly protons with some electrons whereas a outer one mainly has electrons. A part of a belt dips into the upper region of the atmosphere over the South Atlantic to form the Southern Atlantic anomaly. This can present a dangerous hazard to satellites orbiting the Earth. 

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