- The sun, the moon and all those objects shining in the night sky are called celestial bodies
- The celestial bodies which have their own heat and light, which they emit in large amounts are called stars
- Different groups of stars are called constellations. Ex: Ursa Major or Big Bear
- One of the most easily recognizable constellation is the small bear or the Saptarishi, a part of the Ursa Major constellation
- The North Star or the Pole Star indicates the north direction. It always remain in the same position in the sky
- Some celestial bodies do not have their own heat and light. They are lit by the light of the stars. Such bodies are called Planets.
- The word ‘Planet’ comes from the Greek word “Planetai” which means ‘wanderers’.
The Solar System:
The sun, eight planets, satellites and some other celestial bodies known as asteroids and meteoroids form the solar system.
- The sun is about 150 million km away from the earth.
- There are eight planets in our solar system. In order of their distance from the sun, they are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.
- Mercury is nearest to the sun. Takes only about 88 days to complete one revolution
- Venus is considered as ‘Earth’s-twin’ because its size and shape are very much similar to that of the earth.
- ‘Pluto’ may be called a ‘dwarf planet’.
- The earth is the third nearest planet to the sun.
- In size, it is the fifth largest planet.
- It is slightly flattened at the poles. That is why, its shape is described as a Geoid.
- The earth is a unique planet as it has life-supporting conditions like water, air and oxygen.
- Earth is called a blue planet as its two-thirds surface is covered by water.
- The earth has only one satellite, that is, the moon.
- It’s diameter is only one-quarter that of the earth.
- It is about 3,84,400 km away from the earth.
- The moon moves around the earth in about 27 days. It takes exactly the same time to complete one spin.
- A Satellite is a celestial body that moves around the planets in the same way as the planets move around the sun.
- A Human-made Satellite is an artificial body. It is designed by scientists to gather information about the universe or for communication. Some of the Indian satellites in space are INSAT, IRS, EDUSAT etc.
Apart from the stars, planets and satellites, there are numerous tiny bodies which also move around the sun. These bodies are called asteroids. They are found between the orbits of Mars and Jupiter.
The small pieces of rocks which move around the sun are called meteoroids.
A galaxy is a huge system of billions of stars, and clouds of dust and gases. There are millions of such galaxies that make the Universe. Our solar system is a part of the Milky Way galaxy.