When do the Sun and Moon rise and set? When does twilight end and begin? Which planets are up? Set our Online Almanac for your location!

The International Space Station often passes close to the Moon, Sun, and naked-eye planets. Use this tool to plan viewing these close encounters.

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.

This interactive tool is designed to give you answers to your commonly asked questions about your telescope's performance when changing eyepieces and accessories.

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).

Learn the phase of the Moon tonight, the day you were born, or on any historical date.

Now you can calculate the dates and times (local and Universal Times) when the center of the Great Red Spot should cross Jupiter's central meridian, the imaginary line down the center of the planet's disk from pole to pole.

With help from our interactive JavaScript utility, you can always tell which of Jupiter's four largest satellites is which.

With help from our interactive JavaScript utility, you can always tell which of Saturn's brightest moons is which.

Our handy JavaScript utility can help users of large amateur telescopes find as many as five Uranus's brightest satellites.

Our handy JavaScript utility can help users of moderate to large telescopes find Neptune's largest satellite.

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.