If you are in the market for astrophotography equipment, I encourage you to consider Agena Astro. They have a wide variety of telescopes, mounts and related gear in stock, and I have found they provide honest, expert advice. If you use this link to their website you will not pay anything extra and I'll earn a small commission. Thank you.
This is one of the top two sites for buying and selling used astronomy gear, product reviews, and forums where you can discuss any aspect of astronomy with other enthusiasts. A small fee is required.
This site has a lot of capabilities but I use it primarily to figure out how a target (e.g. the Helix nebula) will look in my eyepiece or astronomy camera. You pick your scope, camera, eyepiece and target and the site does the rest.
Probably the best short term astronomy forecasting tool, providing predictions of clouds, transparency and seeing.
Clear Sky Charts
Excellent source of astronomy seeing conditions forecast. Also a great tool for finding observing sites with lower light pollution.
This is one of the top two sites for buying and selling used astronomy gear, product reviews, and forums where you can discuss any aspect of astronomy with other enthusiasts. Free.
Dark site finder
Great website for finding a dark observing location.
Top site for predicting naked eye observations of satellites. See when the ISS is visible in your neighborhood!
For anyone with a small telescope, this is a great site. You can find out when the Great Red Spot and Jupiter's satellite transits are visible.
Solar Dynamic Observatory (SDO)
Find out how the Sun looks right now, at various wavelengths. If you own a solar telescope, this site coupled with Astrospheric is all you need to plan fabulous solar observing!
This site is very helpful in planning an observing evening. It will tell you when any particular target is rising and setting and when is the best time to observe it. This allows you to sequence your observing in a planned manner.
If you are getting into astrophotography and have some basic image processing software (Affinity Photo, Photoshop, GIMP etc) this site allows you to download raw images of deep space objects from telescopes all over the world. You can then process the images yourself. Bronze package costs just $4/month as of Nov 2021.
This site predicts when the International Space Station (ISS) will pass between you and either the Moon or the Sun. The transit itself is less than a second but if you are ready you can get a photo. See my Sun photos for an example.
Possibly the most detailed weather site of the 9 I check regularly. What makes this unique is it provides predictions of not just clouds, but clouds by layers (high, med low) by hour. Very helpful in making decisions about whether to observe at a particular site.