How about a mechanic where the player can take 'photographs' in game and they are scored based on what's in the image + maybe composition and stuff? Kind of like a Pokemon Snap mechanic. That could bring up informational tooltips with info on the stuff in the image you just took.
For example I just took this one as a demonstration [spoiler][img]https://i.imgur.com/H6yJO55.jpg[/img][/spoiler]
Which you could have say,
30 points - 3 * Celestial Bodies
100 points - Planet with life
50 points - Mountain range
200 points - Planetary Rings
100 points - Luminous Galactic Band
480 points - Good Photo!
Did you know: In 2013 astrophysicists predicted that there are 40 Billion Planets in the Milky Way that could support life
or something like that but with more effort
Could be a cool way to integrate social media too with image sharing but that's not something I'd care too much about.
I also think tooltips by themselves would be a neat way to seamlessly educate people on unintuitive space phenomena like Red/Blue Shift or Opposition surge etc.