100 years ago, our understanding of the universe exploded

A mosaic of the Andromeda Galaxy, compiled from 7,398 exposures taken by the Hubble telescope. (NASA/ESA)

Astronomers, maybe more than anyone, appreciate what an island of perfection our Earth is. Our orbit may put us at a perfect distance from the sun for life to flourish, but it is too small to easily help astronomers determine how big the universe is.

Late Renaissance scholar Nicolaus Copernicus suggested that the Earth orbits the sun in 1543, but it took 300 years to prove it.