Interested in astronomy you say? Well mander.xyz describe themselves as a "An instance dedicated to nature and science.". They have a astronomy community with, some activity - !astronomy@mander.xyz. I'm not on mander so I don't know how things are there, but I pretty much don't ever see anyone complaining about it.

feddit.uk is a UK instance. So there might be some interesting things there for you.

lemmy.ee is known for not defederating unless absolutely necessary.

On the topic of defederating, lemmy.world is somewhat disliked due to their defederation happy tendencies. For the most part, though, this whole instance wars thing is mostly due to disagreements on what kind of political discourse should be allowed. Instances like lemmygrad.ml, hexbear.net and lemmy.ml are a bit too left-wing for many people from the center-right to handle: the world views are just too different.

I could rant about the dam instance wars, but it is not what you came were for.