Eli5 How do we measure the distance and magnitude of deep sky objects?

Question

Eli5 How do we measure the distance and magnitude of deep sky objects?

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Answer 1

The farther away something is in space, the faster it’s moving away from us. We can find out how fast it’s moving by looking at the light from it and seeing how much that light has been red shifted. (Think of red shift as the visual equivalent of how sound changes pitch if it moves past you really fast.)

There’s a simple equation that lets us relate this speed to distance. Using the speed we got from red shift, we can get a good estimate of the distance.

Since most deep sky objects are entire galaxies, we can compare how bright they look to other known galaxies to get magnitude.