The universe is commonly defined as the totally of everything that exists including all physical matter and energy, the 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 the universe and each galaxy has, on average, 100 billion stars.
Our galaxy is Milky Way Galaxy( or Akash Ganga) formed after Big Bang.
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.
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.
Satellites are heavenly bodies that revolve around the planets. Moon is the natural satellite of the earth.
Facts about the Moon
|Average distance from Earth||384365 km|
|Rotation Speed||27 days,7 h, 43 min and 11.47 sec|
|Revolution Speed||27 days,7 h, 43 min and 11.47 sec|
|Time taken by moonlight to reach the Earth|| |
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|
|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|
Important facts about the Universe
|Biggest Satellite||Ganymede (Jupiter)|
|Brightest Planet outside the Solar System||Sirius (Dog Star)|
|Closest Star to the Solar System||Proxima Centauri|
|Farthest Planet from Sun||Neptune|
|Planet with maximum number of Satellites||Jupiter|
|Fastest Revolution in Solar System||Mercury|
|Fastest rotation in Solar System||Jupiter|
|Nearest Planet to Earth||Venus|
|Nearest Planet to Sun||Mercury|
|Slowest Revolution in Solar System||Neptune|
|Slowest rotation in Solar System||Venus|
|Smallest Satellite||Deimos (Mars)|
|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.