Higher tier: The light year
The distances between objects in space are huge:
- the distance from one star to another in a galaxy is millions of times more than the distance between the planets in the solar system;
- the distance from one galaxy to another is millions of times more than the distance between the stars in a galaxy.
This means that the numbers used to describe distances in space become very difficult to understand and to write down.
For example, the distance between the Earth and the Sun is about 150,000,000,000 m but the distance to the next nearest star (Proxima Centauri) is 39,900,000,000,000,000 m.
To get around this problem, scientists use the light year as the unit of astronomical distance.
A light year is the distance travelled by light in one year.
So, for example:
It takes light from our Sun about 8 minutes to reach the Earth.
Sun to Proxima Centauri distance is about 4.24 light years.
Sun to the centre of the Milky Way is about 27,000 light years.
The Milky Way is about 100,000 light years across.
Milky Way to Andromeda (the next nearest spiral galaxy) distance is about 2.5 million light years.
