One of the active members of our local club is a very accomplished photographer. He displays at periodic arts and crafts shows and sells them online. (http://astronomy.robpettengill.org). Photography is one art. Painting is another. See Cary Jacobs (Kent, UK) acrylic on canvas advertised on here under Vendors.
Astronomers rely on two broad families of software: planetarium and image processing. In the first category, several commercial products such as Starry Night are well known and compete against free software such as Stellarium and Celestia. Image processing software includes AstroPix and
You can write for publication. The channels are narrow and shallow. In the USA we have two paying magazine, Astronomy and Sky & Telescope. Both are mostly written by their own fulltime staffs. They do accept submissions, subject to a lot of restrictions. Both magazines tell authors to query first. For Astronomy, I found the Guidelines by putting Guidelines in the Search box. I could not find it as a tab, menu item or link off the homepage. Sky & Telescope is more user-friendly. The guidelines for contributors is a labeled link at the bottom of the home page.
If you like buying and selling, astronomy is a hobby that depends on expensive equipment. I will caution that buying and selling is an activity in its own right. In the five years from 1977 to 1982, computer retailers learned that a successful track record in refrigerator sales is a better predictor of success than knowledge of computers. If you do not enjoy trading, knowledge of astronomy will not provide the skills. Those skills can be learned, but it is learning by trial and error which can be expensive. In addition to online venues such as this one and similar discussion boards, local opportunities include flea markets, astronomy clubs, and similar events.
Lecturing for pay is possible. Our local astronomy club does get requests from hotels, resorts, and similar venues to provide guest lecturers for special events. They offer (modest) honoraria that cover time and expenses. You could always do your own advertising and market your own presentation services. However, as with sales, if you do not already enjoy public speaking, knowledge of astronomy will not carry you through public speaking is a learnable skill.
Your city may have a community education effort, perhaps through parks and recreation. Some restrictions may apply as to how and how much you get paid. Here in Austin, Texas, we nothing that I am aware of. However, in Ann Arbor, Michigan, it was an option for people with arts and crafts skills to get paid to mentor other devotees.
That leads to more formal opportunities. Generally, in the USA, you need at least a master's degree to teach at a community college. What that degree is in can be flexible. In larger cities and university towns, talent is easy to find, and you cannot swing a dead
And then there are the online video channels. People love to watch other people doing things. Linking that to advertising displays brings in a revenue stream. Again, it is a mode all of its own. Running a channel successfully can become a commitment you did not plan on simply because people will not return unless you keep posting new material. It is easy to recommend having a dozen or so videos completed before launching the channel. Then you just have to keep up with the viewers by always providing new material.