(a) Stars are big and hot celestial bodies made up of gases. They have their own heat and light, which they emit in large amounts. Planets are also celestial bodies, but they do not have their own heat and light. They are lit by the light of stars.
(b) The Sun, eight planets, satellites and some other celestial bodies known as asteroids and meteoroids form the solar system.
(c) In order of their distance from the sun, the eight planets are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.
(d) Conditions favourable to support life are probably present only on Earth. The Earth is neither too hot nor too cold. It has water and air, which are very essential for our survival. The air has life-supporting gases like oxygen. Because of these reasons, the Earth is a unique planet in the solar system.
(e) The Moon moves around the Earth in about 27 days. It takes exactly the same time to complete one spin. As a result, only one side of the Moon is visible to us on the Earth.
(f) A galaxy is a huge system of billions of stars, and clouds of dust and gases. Millions of such galaxies make up the universe.