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Earth  is the only planet in the solar system  which has not been named after a God. Also known as the Blue Planet, Terra and Tellus, Earth is the 3rd closest planet to the Sun located at a distance of 1.4959789 x 108 km from the Sun. It is the only planet which modern science believes to sustain human life.
Earth was formed around 4.57 billion years ago. Moon, the only natural satellite of Earth was formed about 4.53 billion years ago. The mass of Earth is approximately 5.98 x 1024 kg.

Its astronomical symbol consists of a circled cross, representing a meridian and the equator.

About 70 percent of Earth’s surface is covered by oceans at least 4 km deep. The presence and distribution of water vapor in the atmosphere is responsible for much of Earth's weather.

The blue waters, brown & green land-masses and clouds atop a black background are the distinguishing features of Earth as seen from outer space.

Earth has an oblate spheroid shape, with an average diameter of approximately 12,742 km.

Revolution of the Earth refers to the movement (orbit) of the Earth around the Sun. The Earth revolves around the Sun once every 365 ¼ days. Revolution of Earth causes seasons i.e. summers and winters.



        India                  Arabian Sea             Africa
Rotation of the Earth refers to movement of the Earth about its axis (an imaginary line). The Earth rotates about its axis every 24 hours. Rotation of the Earth causes days and nights. Turning in the eastward direction, the Sun rises in the east and apparently moves toward the west during the day. The Earth then rotates in the opposite direction to the apparent path of the Sun. The rotation of the Earth causes the equator to bulge out slightly such that the equatorial diameter is about 43 km larger than the pole to pole diameter.

Mount Everest (8,850 mts above sea level) in Nepal and the Mariana Trench (10,911 mts below sea level) in the Pacific Ocean are the largest surface deviations known till date on Earth.

The Earth's composition by mass (in percentage) is classified as follows:

Iron:                                34.1
Oxygen:                           28.2
Silicon:                            17.2
Magnesium:                     15.9
Nickel:                            1.6
Calcium:                          1.6
Aluminium:                      1.5
Sulfur:                             0.70
Sodium:                          0.25
Titanium:                         0.071
Potassium:                      0.019
Other elements:               0.53


The average density of Earth is 5515 kg/m3, making it the densest planet in the Solar system. Earth’s core is largely composed of iron (80%), along with nickel and other light elements. The core is divided into two parts, a solid inner core with a radius of 1250 km and a liquid outer core extending beyond a radius of 3500 km. The inner core is composed primarily of iron and nickel. The outer core surrounds the inner core and is composed of liquid iron in a mixture of liquid nickel and small amounts of lighter elements.


Earth's mantle extends to a depth of 2890 km. Iron and magnesium are the two elements which dominate the composition of the mantle. The lower part of the mantle is solid while the upper mantle is semi-molten.


The crust ranges from 5 to 70 km in depth. The temperatures of the crust vary from air temperature on top to about 870 degrees Celsius in the deepest parts of the crust.

Earth's atmosphere

antar2_s.jpgThe Earth’s atmosphere contains roughly 78% nitrogen and 21% oxygen, with trace amounts of other gases. The atmosphere protects life on Earth by absorbing the harmful ultraviolet radiation from Sun, burning out the small & medium meteorites than may harm us etc.


An altitude of 120 km (400,000 ft) marks the boundary line where atmospheric effects become noticeable during re-entry of an object. The Karman line, at 100 km (62 mi), is termed as the boundary between atmosphere and outer space.

Atmospheric layers

The different atmospheric layers can be classified as:

    * Troposphere:
      The troposphere is the lowest layer of the atmosphere starting at the surface going up to between 7 km at the poles and 17 km at the equator. Temperature decreases with height due to cooling.

    * Stratosphere:
      Extends to about 50 km above the Troposphere; temperature increases with height.

    * Mesosphere:
      About 80 km to 85 km above the Stratosphere; temperature decreased with height.

    * Thermosphere:
      More than 640 km from Mesosphere level; temperature increases with height.

The boundaries between these regions are named the tropopause, stratopause, and mesopause.

Various atmospheric regions

    * Ionosphere — the region containing ions.

    * Exosphere — Above the ionosphere, where the atmosphere extends out into space.

    * Magnetosphere — The region where the Earth's magnetic field comes in contact with the solar wind from the Sun. It extends for tens of thousands of kilometers, with a long tail away from the Sun.

    * Ozone layer — Stratospheric ozone is found.

    * Van Allen radiation belts — regions where particles from the Sun become concentrated.


Moon, sometimes also referred to as ‘Luna’, has a diameter about one quarter of the Earth's. It is the largest moon in the Solar system relative to the size of its planet.

The tides on Earth are caused by the gravitational pull of the Moon on the Earth’s surface. The Moon is in synchronous rotation with the Earth and as a result we see the same face of the moon all the time. The reason is that its rotation period is the same as the time it takes to orbit the Earth.
Earth as seen from Moon

Apollo 11 was the first manned mission which landed on the moon carrying commander Neil Armstrong. On July 20, 1969, Neil Armstrong became the first human being ever to land on the moon.

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