Galaxies
The spectra of galaxies look somewhat similar to stellar spectra, as they consist of the light from millions of stars combined. Galactic spectroscopy has led to many fundamental discoveries. Edwin Hubble discovered in the 1920s that, apart from the nearest ones (those in what is known as the Local Group), all galaxies are receding from the Earth. The further away a galaxy, the faster it is receding (see Hubble's Law). This was the first indication that the universe originated from a single point, in a Big Bang.
Doppler shift studies of clusters of galaxies by Fritz Zwicky found that most galaxies were moving much faster than seemed to be possible, from what was known about the mass of the cluster. Zwicky hypothesised that there must be a great deal of non-luminous matter in the galaxy clusters, which became known as dark matter.
Read more about this topic: Astronomical Spectroscopy
Famous quotes containing the word galaxies:
“Don’t you see what’s at stake here? The ultimate aim of all science—to penetrate the unknown. Do you realize we know less about the earth we live on than about the stars and the galaxies of outer space? The greatest mystery is right here, right under our feet.”
—Walter Reisch (1903–1963)