Hubble's Law
Learn more about:

Edwin Hubble

Spectroscopy and Redshift

Big Bang Universe


By the late 1920s, Edwin Hubble had been taking spectra and measuring distances to a large number of galaxies. From each spectrum he learned the galaxy’s redshift, which told him how fast it was moving away from Earth, then he compared that with the object’s distance. What he found set the stage for much of 20th-century cosmology: the farther away the galaxy, the faster it receded. This relation—that a galaxy’s speed is directly proportional to its distance—became known as Hubble’s Law. It was observational proof that we live in an expanding universe, and it helped lay the foundation for the big-bang theory of the universe’s origin.

[Home] [Strange Stuff Explained]

[PBS Online]   [Thirteen Online]