Galaxies, stars and light years
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Explainer Video
Summary
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 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.
 | 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 Light Years. Scientists use the light year as a way of measuring distances between objects in space as it is so big.
 | 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 . It takes light from the Sun about eight minutes to reach Earth.
FAQs - Frequently Asked Questions
How big is the Milky Way galaxy?
The Milky Way Galaxy is 100 000 light years across its diameter.
Which is our closest star?
The closest star is us is the Sun.
What are stars?
Stars are large balls of burning gas.
What is a galaxy made up of?
A galaxy is made up of billions of stars and solar systems held together by gravity.
What is a light year?
A light year is the distance it takes for light to travel in one year.