Emma,
counting stars is a nice way to introduce sampling and estimation with a slightly older class.
With a large image – how do we check how many of a thing are shown? We sample a small part of the image and then multiply it out.
This is particularly important with galaxies, where we have only take deep sky images of a fraction of the sky, so we use the density of galaxies in one area to extrapolate out.
See this article about it: https://www.popularmechanics.com/space/deep-space/a32109712/how-many-galaxies/
The Webb telescope is so good, that galaxies appear in almost every image it takes – even when it is looking at something much closer!
New Webb Image Captures Clearest View of Neptune’s Rings in Decades