Galaxies, stars and light years

In a nutshell

Galaxies are formed of billions stars which are hot balls of burning gas. We live in the Milky Way galaxy, which is $100 000$ light years across. A light year is the distance it takes for light to travel in one year. Scientists use the light year to measure the distances between celestial objects as space is so big.

Definitions

Key word	Definition
Solar System	A group of eight planets, including Earth , and their moons orbiting the Sun
Galaxy	A large group consisting of billions of stars held together by gravity
Light year	The distance light travels in one year
Stars	Large spherical objects of burning gas, which vary in colour and size
The Milky Way	The Spiral Galaxy which the Solar System is in

Galaxies

Galaxies consist of billions of stars, and Solar Systems which are held together by gravity.

Science; Space physics; KS3 Year 7; Galaxies, stars and light years

You may know that we live in the Solar System, which consists of the Sun and eight planets. However, our Solar System is just a tiny part of the galaxy (1.) that you live in, and it is called The Milky Way.

Stars

Stars are large spherical objects of burning gas, and come in many shapes and sizes. Stars also range in colour depending on their temperature and age. The closest star to Earth is our Sun. It may seem very large, but it is an average sized star. The Sun only appears so big because it is close to us.

The light year

The distance from one side of the Milky Way to another is $100 000$ Light Years. Scientists use the light year as a way of measuring distances between objects in space as it is so big.

Science; Space physics; KS3 Year 7; Galaxies, stars and light years

A light year is the distance that it takes light to travel in one year. The diagram on the left shows an example of the sun one light year away from another celestial object (1.).

Light travels at a speed of approximately $300,000,000\ m/s$ . It takes light from the Sun about eight minutes to reach Earth.