Question: How can you tell when a star is born as there are millions?

Nick Wright answered on 13 Mar 2014:

Good question! It isn’t easy, and it’s also not a fast process, a star can take many thousands of years to fully form so its also hard to know exactly what stage of the star formation process counts as the formation of the star. We can observe a lot of stars across our galaxy that are at some stage of the formation process, from very small stars that haven’t fully formed, to larger stars that look like they’re almost finished forming. It can be really useful to astronomers to study lots of different stars forming so that we can fully understand the process.