Edwin Hubble first noticed that the light given off by stars in distant galaxies is shifted toward the red end of the spectrum of light. Red light has a longer wavelength than other colors, indicating these galaxies are moving away from us.
Red shift Term Timeline in A Brief History of Time
The timeline below shows where the term Red shift appears in A Brief History of Time. The colored dots and icons indicate which themes are associated with that appearance.
...galaxies, they had the same missing colors as similar, closer stars, but they were all shifted toward the red end of the light spectrum. The Doppler effect tells us that as something moves away from... (full context)
As Hubble catalogued the galaxies and their distances from us, he found most galaxies were red-shifted, meaning they were moving away from the earth. Indeed, the red shift is proportional to... (full context)
...and glowed brightly. They said it was so long ago that energy would now have red-shifted to become microwave radiation. Penzias and Wilson heard about this, and saw they had already... (full context)