The majority of bright galaxies are either spirals or ellipticals. Faint star clusters, clouds of glowing gas, and galaxies all appeared as faint patches of light (or nebulae) in the telescopes available at the beginning of the twentieth century.

It was only when Hubble measured the distance to the Andromeda galaxy using cepheid variables with the giant 2.5-meter reflector on Mount Wilson in 1924 that the existence of other galaxies similar to the Milky Way in… Spiral galaxies contain both old and young stars, as well as interstellar matter, and have typical masses in the range of 10 9 to 10 12 M Sun .

majority of bright galaxies — either spirals or ellipticals. mass-to-light ratio — the ratio of the total mass of a galaxy to its total luminosity, usually expressed in units of solar mass and solar luminosity; the mass-to-light ratio gives a rough indication…. redshift — when lines in the spectra are displaced toward longer wavelengths (toward the red end of the visible spectrum). Hubble’s law — a rule that the radial velocities of remote galaxies are proportional to their distances from us.