It is very rare that I do a repost of a blog, but this time I had to make an exception. Each day our friends over at Astrobites summarize a paper on ArXiv (or produce some other, similarly interesting blog post) written at an undergraduate readership level. Yesterday's post discussed how brightness from stars (i.e. photometry) is actually measured:
It goes into some discussion of spectral types and filters so it's well worth a read if you have some time to spare.