Key Points - Stars and the Solar System

- The phases of the moon occur because we can see only that part of the moon which reflects the light of the Sun towards us.
- Stars are celestial bodies that emit light of their own. Our sun is also a star.
- It is convenient to express distances of stars in light years.
- Stars appear to move from east to west.
- The pole star appears to be stationary from the Earth, because it is situated close to the direction of the axis of rotation of the Earth.
- Constellations are groups of stars that appear to form recognisable shapes.
- The solar system consists of eight planets and host of asteroids, comets and meteors.
- A body revolving around another body is called a satellite.
- Moon is the natural satellite of the Earth. Some planets also have natural satellites.
- Venus is the brightest planet in the night sky.
- Jupiter is the largest planet of the solar system.
- The artificial satellites revolve around the Earth. They are much closer than the moon.
- Artificial satellites are used for weather forecasting, long distance communication and remote sensing.
- Sun: It is the source of almost all energy on Earth. It continuously emits huge amounts of heat and light.
- Planets: A planet has a definite path in which it revolves around the sun called orbit. Time taken by a planet to complete one revolution increases as the distance from the sun increases.
- There are eight planets in our solar system: Mercury, Venus, Earth, Mars, Jupitar, Saturn, Uranus, Neptune.

- Other members in our solar system are:
(i)  Asteroids: These are rocky planetary bits orbiting around sun. asteroid belt lies between Mars and Jupiter.
(ii) Comets: These are heavenly bodies that revolve around the sun. It appears generally as a bright head with a long tail.
(iii) Meteors and Meteorites: Meteor is a brief streak of light in the night sky caused by a meteoroid. Smalle meteors melt and burn up creating streaks of light. Few meteoroids which survive as they pass through the Earth’s atmosphere and reach the Earth surface are called meteorites.
(iv) Artificial Satellites: Man-made objects sent into space to orbit the earth. Example: IRS, EDUSAT, INSAR.

- Constellations: A group of stars forming some kind of recongnisable figures or patterns are known as constellations.
- Constellations appear to move from east to west as Earth rotates from west to east.
- Orion- the Hunter, Ursa Major- the Great Bear or Saptarishi, Cassiopeia are some constellations.