Light Pollution Map: A color coded interactive map of light pollution around the world with Bortle scale and more.
Stellarium: A free and open source planetarium for your PC that has just about everything you could ever need to find a wide swath of deep space objects and so much more.
PolarFinder: A free PC based polar alignment tool used for aligning your equatorial mounts with alignment scopes.
Night Sky Gazing: This website helps people to get into amateur astronomy. It describes easy targets for observations, explains telescope types and characteristics, and helps to make first steps in astrophotography.
A Beginner’s Guide to Choosing Equipment for Deep-Sky Electronically-Assisted Astronomy (EAA): Call it what you will, electronically-assisted astronomy is becoming a popular pastime for several reasons.
Create your own Sun/Moon Rise/Set Calendar: SunriseSunset.com provides free custom calendars for any location around the world with sunrise, sunset, moonrise, moonset, moon phases, solstices, equinoxes, and dawn, dusk and other twilight times
Moon Calendar: Moon rise, Moon Set and Moon Phases Calendar
Telescopius (Astronomy Planning Made Easy): Telescopius mission is to help astronomers. Once you set your observing location and date (you can save frequent locations), all rise/transit/set times reported throughout the app will be calculated for your selection; you’ll see how the moon will look like that day, sun and moon rise/set times, and weather information if available. When you are ready to find targets for your telescope, in the Targets menu you’ll find Deep Sky objects like galaxies and nebulae, and Solar System objects like planets, comets and asteroids. You can filter Deep Sky Objects to see only those which will stay above certain altitude for at least some amount of time to make your subs and you can create your personal observing lists. Finally, you can use the Telescope Simulator to check camera and eyepiece framing. You can plan mosaics too and get the center coordinates for each pane very easily.
44 Closest Stars compared to the Sun: 44 Closest stars and how they compare to the sun.
Astrospheric: Astropheric provides advanced weather tools for astronomers in the continental US and Canada.
Legacy Survey Org: DESI Legacy Imaging Survey consists of ~14,000 square degrees of extragalactic sky visible from the northern hemisphere in the optical and infrared. The site has not only data on objects surveyed but an incredibly useful viewer to be able to see various objects surveyed.
The 88 Constellations and Their Brightest Stars