Create a custom, naked-eye map of the whole sky for any place on Earth, at any time of day or night, on any date from 1600 to 2400.
When do the Sun and Moon rise and set? When does twilight end and begin? Which planets are up? Start your night of observing with our Astronomical Almanac.
Learn the phase of the Moon tonight, the day you were born, or on any historical date.
Use our interactive observing tool to say which of the planet's four largest moons is which.
Calculate when the Great Red Spot will cross Jupiter's central meridian — that's the best time to see the famous storm through your telescope.
Find information on observing Jupiter during its 2016 - 2017 apparition, including information on its moons and Great Red Spot transit predictions.
Take the observing challenge: Find as many as five of the brightest moons of Uranus in a large backyard telescope using our interactive observing tool.
Triton, Neptune's largest moon, is a tricky find. Our Triton Tracker observing tool can help users of moderate to large telescopes spot this distant moon.
To compare what you see on Mars with a map, you need to know which side of the planet you're looking at. Our handy Mars Profiler tells you that and more, for any date and time.
Use this telescope calculator to tell you how changing out eyepieces and accessories will affect your telescope's performance.
The International Space Station passes over virtually all of Earth's populated areas, and you can spot it easily with your eyes alone — if you know where and when to look for it.
The International Space Station often passes close to the Moon, Sun, and naked-eye planets. Use this tool to plan viewing these close encounters.
Now you can calculate the dates and times (local and Universal Times) when the eclipsing variable star Algol should be at its dimmest (magnitude 3.4 instead of its usual 2.1).