Indira Gandhi Planetarium, Lucknow Veer Bahadur Singh Planetarium, Gorakhpur        Aryabhatt Planetarium, Rampur

Earth

EARTH is the only planet known to support life. All of the things we need to survive are provided under a thin layer of atmosphere that separates us from the uninhabitable void of space. Earth is made up of complex, interactive systems that are often unpredictable. Air, water, land, and life—including humans—combine forces to create a constantly changing world that we are striving to understand.
Earth is the third planet from the sun and the fifth largest in the solar system. Earth's diameter is just a few hundred kilometers larger than that of Venus. The four seasons are a result of Earth's axis of rotation being tilted more than 23 degrees. Nearly 70 percent of Earth's surface is covered by water. The presence and distribution of water vapour in the atmosphere is responsible for much of Earth's weather.
Earth takes approximately 365.25 days to complete one revolution around the Sun in a slightly elliptical orbit and 24 hours to rotate at its own axis.Earth's polar axis is inclined 23.5 degrees from the perpendicular to the ecliptic and because the Earth exhibits parallelism as it revolves about the Sun.  

Internal Structure of Earth:
The inner part of the earth, Core, is about 1,800 miles (2,900 km) below the earth's surface.The core is a dense ball of the elements, iron and nickel. It is divided into two layers, the inner core and the outer core. The inner core - the center of earth - is solid and about 780 miles (1,250 km) thick. The outer core is so hot that the metal is always molten.
The layer above the core is the mantle.The mantle is to divide into the inner mantle and the outer mantle. It is about 1,800 miles(2,900 km) thick and makes up nearly 80 percent of the Earth's total volume.
The crust lies above the mantle and is the earth's hard outer shell.In relation with the other layers, the crust is much thinner. The crust is made up of solid material but these material is not everywhere the same. There is an Oceanic crust and a Continental crust. The first one is about 4-7 miles (6-11 km) thick and consists of heavy rocks, like basalt. The Continental crust is thicker than the Oceanic crust, about 19 miles(30 km) thick.

Atmospheric Composition of Earth:
Components   Percentage Composition  
nitrogen   78% of atmosphere  
oxygen   21% of atmosphere  
trace gases   1% - Neon, Helium, Hydrogen, Methane, Carbon dioxide