Measuring distances in space
The distances to stars and galaxies are so large that miles and kilometres are meaningless.
The Sun is 150 million kilometres or 93 million miles from the Earth, but that鈥檚 a tiny distance compared with the distance to other stars, or other galaxies.
Larger units of length are used for these measurements.
One popular one is the light-year.
Light years
A light year is the distance light travels in a year.
It takes light over four years to reach us from the next nearest star, Proxima Centauri.
We say that the distance to Proxima Centauri is 4.2 light years.
It takes over 100,000 years to cross our galaxy, the Milky Way.
We say that the diameter of the Milky Way is 100,000 light years.
The most distant galaxies observed are about 13,000 million light-years away.