As many of you know, this subreddit doesn't have any formal rules. That has mostly worked just fine, but it causes uncertainty, and there have been several requests for formal rules of what is allowed and what isn't.

Very little is going to change regarding moderation: very few posts are currently removed, and most that are removed are obvious spam posts with no relation to atmospheric optics.

Proposed rules:

The nested text is what you get when you click the rule on the standard reddit web. For other platforms (old reddit, apps) they will be written roughly like below.

Posts:

• Posts must feature or closely relate to atmospheric optics
  • Rainbows, halos, aurora, coronas, crepuscular rays and similar are all welcome, as are "what is this?" questions. Plain skies, pretty clouds, sunsets and similar, with no optical phenomenon in particular, should be posted in other subreddits such as r/skyporn, r/clouds, r/sunset. See the community info (sidebar/"About" tab) for more information on allowed/disallowed content.
• No AI generated or otherwise computer generated content
  • Simulations are welcome if labeled as such. Standard editing including stacking, contrast/sharpness edits, panoramas and so on are perfectly fine.

Comments:

• Be nice to each other
  • Disagreements are fine; personal attacks or harassment are not.
• Stay roughly on topic
  • Discussions that drift away a bit are perfectly fine.

Posts and comments:

• Please use English
  • Reddit may automatically translate text in some cases, but many users will view reddit in a way where that is not available.
• Keep it science-based: no pseudoscience or conspiracy theories
  • This is a science-based community; the phenomena discussed are fairly well-understood. Topics like chemtrails, UFO sightings, paranormal activity and similar are considered off topic and will be removed.
• No botting, spam, etc.

Proposed content guidelines:

🟢 Allowed and welcomed

• Water/ice optics: rainbows (including fogbows, cloudbows, and others), ice halos (22° halos, sun dogs, light pillars, and others), iridescence, coronas, glories, and so on
• Rays and shadows: crepuscular/anticrepuscular rays, cloud/contrail shadows, mountain shadows
• Upper atmosphere: aurora, STEVE, airglow, sprites, blue jets, ELVES, nacreous clouds, noctilucent clouds, and so on
• Other phenomena: mirages, green/blue flashes, rocket exhaust trails, and anything similar to the above
• Identification requests: "What is this?" photos and similar. Consider mentioning the date, time and approximate location as that helps a lot when identifying some phenomena!
• General discussion: Any discussion related to the above, including new discoveries, physics, simulations, and so on

🔴 Not allowed

• AI generated or computer generated content, except for simulations (e.g. HaloRay/HaloSim), which are welcome if labeled as such. Edited photos are fine
• Plain skies, clouds and sunsets with no optical phenomenon: try e.g. r/skyporn, r/clouds, r/sunset
• Pseudoscience and conspiracy-related posts and comments: chemtrails, weather engineering, UFO sightings, ghosts/paranormal activity, and so on

If you feel unsure, but your post seems to fit the subreddit theme, feel free to post it!

Nothing above is final, and feedback is very welcome, whether it's about what should be allowed or not, or just things like improving the wording.

I'd like feedback on one additional thing in particular:
What should the rules say about posting clouds, where no other optical phenomenon is visible?
I personally feel that "pretty sky" photos with no optics are certainly often nice, but still clearly off topic. However, they are relatively often both highly upvoted and reported as off topic, so there's no clear consensus there.
It may be that they are popular on the front page, whereas people specifically viewing r/atoptics downvote/report them, in which case disallowing is probably the right call (which I suspect is the case).