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Redshift

Redshift is the phenomenon where light from distant galaxies is stretched to longer, redder wavelengths due to the expansion of the universe. It serves as a key observational evidence for the universe's ongoing expansion.

Source: science.nasa.gov

APODs including "Redshift"

The Galaxy and the Quasar

07/10/2002

The Galaxy and the Quasar
Image Credit: NASA Astronomy Picture of the Day

Is the galaxy in the center connected to the quasar on the upper right? Disagreements about systems like this have raged for decades and have been used to challenge the foundations of modern cosmology. Some believe that the quasar Markarian 205 was recently ejected from galaxy NGC 4319, indicating that the high redshift of Markarian 205 is not indicative of its distance. Most astronomers have come to believe, however, that the two are not physically associated, and that the high redshift of Markarian 205 indeed indicates that it lies across our universe. In this predominant view, as with a tree branch that happens to point toward the Moon, their juxtaposition in the above image is just coincidence.