Now that you've got moderators, you can edit the on-topic page in your help center! Cheers!
Now what do you put there? Post your points in the answers below, and vote for them.
Astronomy Stack Exchange is a Question and Answer site about astronomy and astronomy related topics; the study of objects and matter outside the Earth's atmosphere and of their physical and chemical properties
The purpose of this site is to provide expert level answers to questions on:
Setting up, using and maintaining your astronomy related equipment
Astronomical observations, for all celestial objects across the entire spectral range.
Astrophysics and Cosmology
Planetary Science and Celestial mechanics
Data returned by space missions such as probes, rovers and satellites
What type of equipment will allow you to see a certain entity
What questions are off topic here?
Earth science, unless directly related to phenomena observable on other celestials, Solar system in general of which Earth is a constituent part, or as an origin of observational astronomy where its movement, local and global phenomena might affect observations and measurements in any way, is off-topic on Astronomy but can be asked on Physics now or Geoscience once this Stack Exchange site proposal reaches public beta.
Questions about maintenance and general use-age of equipment such as the Curiosity Rover. A question can be about data returned by these pieces of equipment, such as atmospheric composition and planetary composition, but questions about the tools on the rover or how the rover cleans its solar panel are off-topic
Questions that are purely hypothetical, for example a question such as 'Could a black hole destroy the universe' or 'What if our solar system had two suns'
Questions about artificial satellites whose purpose is not directly related to astronomy. You may ask about their orbit, but not their purpose, use-age and safety features
Questions asking for a specific brand or model of telescope, these are very time and opinion specific and are likely to incite debate
For more help, see What types of questions should I avoid asking?
How should I give an on-topic answer?
Make sure your answer adds helpful information and is a complete, stand-alone answer. Read other answers first and be sure not to completely restate information that has already been posted.
Good answers should explain why their objective information is accurate either by properly sourcing their answer or by giving enough details that the results could be derived by someone else. This is science after all!
We don't have strict formatting guidelines for citations, but a couple of links to sources doesn't hurt--and keep in mind that not all sources are equal (academic papers are generally better than Wikipedia). Where answers are derived from physical documents, mentioning the title of the source is good, but a formatted citation (using your preferred style) is better.
If you are answering a question with a more subjective bent, or if you want to take on your opinion to an already objective answer, it is fine to simply state that it is your opinion. At least this explains to everyone else where your information comes from.
Can I just use Wikipedia as my source for everything?
Whilst Wikipedia does have a wide range of information there is no way for us to measure its accuracy or validity as it is very easy for the displayed information to change over time, this has knock-on effects when the information changes drastically, perhaps due to a recent discovery.
Where possible try to use reputable sources, there are lots of astronomy and space related site out there, not least of which is NASA, and please don't forget that your source doesn't have to be a website! It could be a paper or even an astronomy magazine in some cases.
Overall you can use Wikipedia sparingly, but if you can back this up with other sources too then this is preferred.
Please look around to see if your question has been asked before. It’s also OK to ask and answer your own question, in fact this type of interaction is encouraged, especially for difficult experiences of yours!
If your question is not specifically on-topic for Astronomy.StackExchange, it may be on topic for another Stack Exchange site. If no site currently exists that will accept your question, you may commit to or propose a new site at Area51, the place where new Stack Exchange communities are democratically created.
This site is for the observational science of Astronomy: how to gather data, where to look for it, with what equipment, who has done what, how we define / catalogue something, also discussing other astro societies, events, e.t.c.
I'm paraphrasing TildalWave. Feel free to edit this into a better format for the help center.