Question: How do scientist determine what objects and things are in what galaxy?

Jack Carlyle answered on 11 Nov 2015:

A lot of the time astronomers use the colour of light coming from galaxies to figure out what is in them. Older stars tend to be more blue, while younger stars tend to be more red (on average – though as usual, reality is always much more complicated than this!).

We can go even further and use something called “spectroscopy” to figure out which elements are in a galaxy. This looks at very specific colours of light (not just “red” or “blue”, but with precisely determined “wavelengths” of photons) which are emitted by various elements.

There are other methods, too, but since looking at light is the easiest thing to do with such faraway objects, this is the main way we tend to do things. If you’re interested in this, you should think about becoming an astronomer! It’s a fascinating and beautiful pursuit.