Stars and the Solar System Class 8 Notes CBSE Science Chapter 17 (Free PDF Download)

Celestial bodies: All natural bodies visible in the sky, outside the Earth's atmosphere, constitute the celestial bodies, e.g., stars, planets, their moons, comets, asteroids, meteors, etc. 

Stars: Celestial bodies which have their own heat and light are called stars. The sun is also a star.

Constellations: A group of stars forming some kind of recognizable figures or patterns are known as constellations. Constellations are useful in assisting astronomers and navigators to locate certain stars.

The north star is also known as the Pole star. It helps us in determining direction. It always remains in the same position because it is situated close to the direction of the axis of rotation of the Earth.

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.

Solar system: The sun, eight planets, satellites and some other celestial bodies known as asteroids and meteoroids form the solar system.

Sun: It is the centre of the solar system. It is huge and made up of extremely hot gases. It provides the pulling force that binds the solar system. The sun is the ultimate source of heat and light for the solar system. It is a dwarf star.

Planets: There are eight planets in our solar system. All the eight planets of the solar system move around the sun in fixed paths. These paths are elongated and are called orbits.

Dwarf Planets: A celestial body resembling a planet but lacking certain technical criteria that are required to be a planet. 

The time taken by a planet to complete one full revolution around the sun is called it is period of revolution. The time taken by a planet to rotate a full 360 degrees on its axis is called it is period of rotation.

In order of their distance from the sun, planets are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. 

All the planets rotate in the east to west direction except Venus it rotates in the west to east direction.

Mercury is the smallest and fastest planet.

Venus is also known as an evening and morning star because it is the brightest planet.

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. It is also known as the blue planet.

Mars has a dusty, cold deserted world with two moons Phobos and Demos.

Jupiter is the largest planet.

Uranus rotates at a 90-degree angle from the plane of its orbit

Moon is Earth's only natural satellite. Its diameter is only one-quarter that of the earth. 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.

A Satellite: It 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. It also helps us in weather forecasting. Some of the human satellites are INSAT, IRS, EDUSAT etc.

Asteroids: These are minor rocky airless remnants leftover of planets from the early formation of our solar system. They are found orbiting the sun between Mars and Jupiter.

Meteoroids: These are chunks of rock or particles of debris in our solar system. Range in size from dust grain to small asteroids 

Meteors: When a meteoroid enters the earth’s atmosphere or atmosphere of another planet at high speed and burns up. The fireballs or shooting stars are called meteors.

Meteorite: When a meteoroid survives a trip through the atmosphere and the ground it is called a meteorite.

Comets: these are the frozen leftovers from the formation of the solar system composed of dust, rock and ice. As they orbit closer to the sun, they heat up and spew gases and dust into a glowing head that can be larger than a planet and forms a tail that stretches millions of miles.