Stars and The Solar System
Category : 8th Class
Stars and the Solar System
Synopsis
- Universe is a vast collection of stars, planets, nebulae, galaxies, intergalactic matter and everything that exists in them. It is believed to have been formed 15 billion years ago from a huge explosion called 'Big Bang’
- To measure distances on astronomical scale, the unit light year is used. It is the distance travelled by light in one year. 1 light year \[=9.46\times {{10}^{12}}\,km.\]
- Stars are self-luminous, astronomical bodies which produce energy from nuclear fusion reactions. They form from a large collection of gases called nebulae.
- A galaxy is a group of billion stars and other celestial bodies. Galaxies exist in different shapes such as circular/elliptical, ring and irregular. They usually revolve around themselves and move away from each other at tremendous speeds.
- A group of stars which seem to form a pattern is called a constellation. e.g., Big bear, Orion etc.
- Sun along with its nine planets/their satellites, asteroids and comets are together named as solar system.
- Planets like Mercury, Venus and Mars have internal structures similar to that of the earth. So, they are called terrestrial planets. Jupiter, Uranus, Saturn and Neptune are mainly made up of gases. They are called gas planets.
- Asteroids are irregular, rocky bodies that revolve around the sun between the orbits of Mars and Jupiter.
- A comet is a small body of rocks, ice and gases that revolve around the sun in a highly eccentric, elliptical orbit.
- A man-made spacecraft orbiting around an astronomical body is called a satellite. If the orbit of a satellite is synchronised with the earth's rotation/it is called a geostationary satellite. If a satellite seems to be stationary from the point of view of the sun, it is called the sun synchronous or polar satellite.
- Satellites are used for communication, weather forecasts, remote sensing, conducting scientific experiments and for various other military uses.
- The various shapes of the bright part of the moon as seen during a month are called phases of moon.
- A planet has a definite path in which it revolves around the sun. This path is called an orbit.
- The axis of earth is inclined to its orbital plane at an angle of \[66.5{}^\circ \]. This inclination helps in the change of seasons on the earth.
- The time taken by a planet to complete one revolution around the sun is called the period of revolution, while the time taken to complete one round around its own axis is called the period of rotation.
