A zettametre (Zm) is an SI unit of length representing 10^21 metres, which is approximately 105,700 light years. This unit is perfectly scaled for measuring the diameter of galaxies. For example, the Milky Way galaxy is roughly one zettametre across. It is a standard unit in galactic astronomy and cosmology.
Heard on the job
The diameter of the Andromeda galaxy is roughly two zettametres.
Also heard as
- zettameter