How the space and astronomy communities compare
Membership is concentrated: the three largest communities hold 90% of all members on this list, so most of the space and astronomy conversation happens in a handful of places. r/space and r/Astronomy are the two busiest, with roughly 26 and 27 new posts a day. Per member, the liveliest is r/universe: 12 posts a day from 29.6K members — a smaller crowd, but an engaged one. Among the communities we track weekly, r/Astronomy grew fastest recently (+0.08%, +2.5K members since Oct 19). The oldest is r/space, founded in 2008, and every community here is more than five years old — this is a long-established corner of Reddit.
The 11 biggest space and astronomy subreddits
r/space 27,990,867 members · ~26 posts/day · +3.9K since Oct 19 · since 2008Share & discuss informative content on: * Astrophysics * Cosmology * Space Exploration * Planetary Science * Astrobiology
r/nasa 5,882,842 members · ~6.0 posts/day · +926 since Oct 19 · since 2008r/NASA is for anything related to the National Aeronautics and Space Administration; the latest news, events, current and future missions, and more.
- Sr/spacex ↗ 3,700,666 members · +622 since Oct 19 · since 2011
Welcome to r/SpaceX, the premier SpaceX discussion community and the largest fan-run board on the American aerospace company SpaceX. We recommend using r/SpaceX with Old Reddit. This board is not an official outlet for SpaceX inf…
r/Astronomy 3,155,879 members · ~27 posts/day · +2.5K since Oct 19 · since 2008The amateur hobby of humanity since the dawn of time and scientific study of celestial objects.
- Sr/SpaceXLounge ↗ 382,542 members · ~5.7 posts/day · since 2016
Welcome to r/SpaceXLounge, the sister subreddit to r/SpaceX, and a place for relaxed and laid-back discussion. We recommend Old Reddit with r/SpaceXLounge. This subreddit is not an official outlet for SpaceX information. This is …
- Sr/Starlink ↗ 231,555 members · ~23 posts/day · since 2008
r/Starlink is for news, media, and discussions related to Starlink, the SpaceX satellite internet constellation. This is a fan-run Subreddit. For official news and to sign up for service, visit starlink.com
- Ar/askastronomy ↗ 106,570 members · ~15 posts/day · since 2012
For your astronomy-related questions and content!
- Ar/astrophysics ↗ 102,424 members · ~6.7 posts/day · since 2010
The branch of astronomy concerned with the physical nature of stars and other celestial bodies, and the application of the laws and theories of physics to the interpretation of astronomical observations.
- Sr/SpaceXMasterrace ↗ 91,126 members · ~7.7 posts/day · since 2014
A subreddit for the great Space X masterrace to discuss the words of EloN and his Glorious company Space X. SMART discussion about other rockets is also ok
- Sr/SpaceForce ↗ 31,109 members · ~2.3 posts/day · since 2017
Community for current, future, and past members of the US Space Force. The Space Force is not the same thing as US Space Command; the USSF is a service branch and SPACECOM is a combatant command.
- Ur/universe ↗ 29,576 members · ~12 posts/day · since 2009
The Universe is a forum for sharing and discussion of Astronomy, Astrophotography, Astrophysics & Cosmology.
What these communities upvoted this week
A cross-section of this week's top posts from the bigger space and astronomy subreddits, in the order Reddit ranks them.
- Astronomer here! Big news- I am a winner this year for the Wendy and Eric Schmidt Awards for Excellence in Science Communications, in large part for my posts on Reddit!r/space · Oct 27
- I designed and 3D printed a 60cm Saturn V cutaway to show the engineering inside!r/nasa · Oct 25
- Toronto, Canada photographed from the International Space Stationr/space · Oct 24
- Latest estimate for Starship launches required to support a Moon landing? 22.r/nasa · Oct 25
Choosing where to post
Questions do best in r/askastronomy, the community on this list that is built around advice and help (around 15 posts a day).
Big subreddits give a post the widest audience, but they also bury it quickly; the mid-sized communities on this list are usually friendlier for questions and first posts. Always read the rules in the sidebar first — each community is run by its own volunteer moderators. Our guide to searching Reddit explains how to dig through any of these communities, and the subreddit info tool gives you the stats of one we don't list.
Frequently asked questions
Which space and astronomy subreddit has the most members?
r/space is the largest, with 27,990,867 members, followed by r/nasa (5.9M) and r/spacex (3.7M).
Where are the most new space and astronomy posts?
By new posts per day, r/Astronomy leads with about 27, ahead of r/space (26). Counts are averages over the last seven days.
Which space and astronomy subreddit is best for questions?
r/askastronomy is the one built around questions and advice, with about 15 new posts a day. Check its rules and search it first — common questions have usually been answered.
How many space and astronomy communities are on this list?
We list 11 active, safe-for-work space and astronomy communities with at least 25,000 members each, 41.7M members in total (people can be in several). Reddit has many smaller ones too; our guide on searching Reddit shows how to find them.
What is the oldest space and astronomy subreddit?
r/space, created on Jan 26, 2008.
Are these space and astronomy subreddits safe for work?
Yes. Every community on this page is public and not marked 18+ by Reddit, and we filter out communities whose name or description points to adult content.
Data: Reddit's public subreddit search and the Arctic Shift archive (Oct 30, 2026), growth from SubMouse's weekly snapshots. Member counts of communities outside our Top 1000 come from the archive and can lag a little. Not affiliated with Reddit.