universe is commonly defined as totally of everything that exists including all physical matter and energy, planets, stars, galaxies, and the contents of intergalactic space. The study of the universe is known as Cosmology.


A galaxy is a vast system of billions of stars, dust, and light gases bound by their own gravity. There are 100 billion galaxies in universe and each galaxy has, on average, 100 billion stars.

Our galaxy is Milky Way Galaxy( or Akash Ganga) formed after Big Bang.

Andromeda is nearest galaxy to Milky Way.

The Big Bang Theory

Big Bang Theory was an explosion of concentrated matter in the universe that occurred 15 billion years ago, leading to the formation of galaxies of stars and other heavenly bodies.

It is believed that the universe should be filled with radiation called the cosmic microwave background. NASA has launched two missions to study these radiations, i.e, the Cosmic Background Explorer (COBE)  and the Wilkinson Microwave Anisotropy Probe(WMAP).


Atars are the heavenly bodies made up of hot burning gases and they shine by emitting their own light.

Night Sky with Stars and Galaxy
Night Sky with Stars and Galaxy

Black Hole

Stars having a mass greater than three times that of the Sun, have very high gravitational power so that not even light can escape from its gravity and hence called black hole.


Comets are made up of frozen gases. They move around the Sun in an elongated elliptical orbit with the tail always pointing away from the Sun.

The sky is divided into two units to enable the astronomers to identify the position of the stars. These units are called . There are 88 known .


Satellites are heavenly bodies that revolve around the planets. Moon is the natural satellite of the earth.

Facts about the Moon


3476 km
Average distance from Earth 384365 km
Rotation Speed 27 days,7 h, 43 min and 11.47
Revolution Speed 27 days,7 h, 43 min and 11.47
Time taken by moonlight to reach the Earth


Solar System

The Solar System consists of the Sun, the eight planets, and their satellites and thousands of other smaller heavenly bodies such as asteroids, comets, and meteors.

The Sun is at the centre of the solar system and all these bodies revolve around it. It is the nearest star to the earth.

Facts about the Sun

Average distance from the Earth 149598900 km
Diameter 1391980 km
Temperature of the Core 15000000°C
Rotation Speed 25.38 days
Time taken by the Sunlight to reach Earth 8 min and 16.6 sec
Solar system planets set. The Sun and planets in a row on univer
Solar system planets set. The Sun and planets in a row on univer

Important facts about the Universe

Biggest Planet Jupiter
Biggest Satellite Ganymede (Jupiter)
Blue Planet Earth
Green Planet Uranus
Brightest Planet Venus
Brightest Planet outside the Solar System Sirius (Dog Star)
Closest Star to the Solar System Proxima Centauri
Coldest Planet Neptune
Evening Star Venus
Farthest Planet from Sun Neptune
Planet with maximum number of Satellites Jupiter
Fastest Revolution in Solar System
Hottest Planet Venus
Densest Planet Earth
Fastest rotation in Solar System Jupiter
Morning Star Venus
Nearest Planet to Earth Venus
Nearest Planet to Sun
Red Planet Mars
Slowest Revolution in Solar System Neptune
Slowest rotation in Solar System  Venus
Smallest Planet
Smallest Satellite Deimos (Mars)
Earth’s Twin Venus
Only Satellite in the atmosphere like Earth Titan
Average distance of Sun from Earth 149598900


Small planetary bodies that revolve around the Sun and found in between the orbits of Mars and Jupiter. Also known as minor planets.

Meteors and Meteorites

Meteors are also called shooting stars. Meteors are fragments of rocks coming towards the Earth. They are formed due to collision among the asteroids.

Meteors that do not burn up completely in Earth’s atmosphere and land on the Earth, are called meteorites. Meteorites are composed of various proportions of a nickle-iron alloy and silicate minerals.

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