Astronomers do it while gazing at Uranus. Astronomers do it with binaries. Astronomers do it with dwarfs. Astronomers do it with giants. Astronomers do it with lenses.
Astronomers do it with light.
Astronomers do it with lights out. Astronomers do it with long tubes. Astronomers do it with mirrors. Astronomers do it with sextants. Astronomers do it with stars.