Astronomers measure the resolving power of a telescope in terms of degrees.
Degrees are further divided into arcminutes and arcseconds. 3600 arcseconds The best telescopes on the ground can rarely see detail that is less than 1 arcsecond wide or differentiate between two stars that are less than 1 arcsecond apart in the sky. This is because turbulence in Earth's atmosphere causes images to ripple and shimmer. This is one of the main reasons astronomers like to use Hubble.