For example, the further a galaxy is from us, the more red it is.
In: Planetary Science
Redshift generally happens when an object moving away from the observer emits light towards the observer. The wavelength of the light increases – This is called the dopper effect. We know the amount of redshift that has happened by comparing known spectral lines against observed spectral lines.
The reason we see Galaxies redshifted is because the universe is expanding, and thus, galaxies appear to be moving away from us at some high velocity. Think of spacetime as the surface of a balloon and two Galaxies as 2 random points on the surface of the balloon. As the balloon inflates, the distance between the two points increases, too. Relative to one point, the other point would appear to move away at some velocity. That’s a simplified 2d analogy of the expansion of the universe.
*Notice that space is basically being created in between the 2 points in the balloon, that is true for Galaxies as well.*
Now picture a photon of 10 units wavelength traveling from a distant galaxy to you. As the universe expands, the photon also expands. As it crosses light years and light years and reaches you, all the amount of expansion that the universe had undergone is “imprinted” into that photon’s wavelength. Viz. The wavelength of the photon might end up as 87 units. Now we can isolate a factor of expansion here *z*, which is defined as *z*+1=wavelength observed/original wavelength, in this case, *z* being 7.7. This factor *z* is known as cosmological redshift, which is a crude indicator of distance traveled.
As you can easily see, the farther the galaxy is, the more time photons from that galaxy get to “expand”, and thus the redshift on those photons get higher.
Edit:Grammar and formatting
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