One of the first things to know (and teach) about galaxies is that they consist of *stars*. I've tried to capture that in the attached image I just prepared for my lecture, of M31 (Andromeda Galaxy) with two heavily zoomed-in insets. (Background mine, zoomed-in data PHAT.) 🔭🧪 1/

You win the jar of jelly beans if you can guess how many are in it

Don't they consist of stars, planets, asteroids, meteors, dust, and gas, not to mention empty space bubbling with virtual particles? 🤔

I recall from astronomical history when the nature of galaxies was unclear and they were described as ‘nebulae’…!

People still using phat? 😁

A great combination of images that really puts this into perspective. I feel like there's a Dave Bowman quote that applies here. And when you then remember Hubble's ultra-deep field in this context, the mind blows.

Some things to notice here: In the insets, you can make out individual stars that, in the background image, blur to look like a continuous surface. The insets are from the really nice Hubble images by Julianne Dalcanton et al. as part of the PHAT survey. astro.berkeley.edu/research-fac... 2/

this is cool This actually brings to focus the incomprehensible density of stars in Andromeda Love to see it 🫡