Try !astronomy@mander.xyz
Mander is generally a science-focused instance, so there are a lot of sciency /c's there
Here's one:
https://kbin.social/m/space !kbin.social/m/space
(Can't remember which linking format works best, so I did both)
Also, this happened to be at the top of my feed earlier, but it wasn't from a dedicated community:
!lemmy.world/post/2671971