Star Map and Constellations
The real sky, calculated in your browser for any place and time. Drag to look around, scroll or pinch to zoom, and tap anything to learn about it. Your location is never sent anywhere.
How to use the map
Sky tonight shows what is above your horizon at the time and place you choose, as if you were standing there looking up. The green circle line is the horizon, with the compass directions along it. Use the Look buttons to turn to north, east, south, west or straight up. Star atlas is a map of the whole sky with right ascension and declination (the sky’s longitude and latitude) that you can drag and zoom without the ground in the way.
Navigation: drag to move, scroll wheel, pinch or the + and − buttons to zoom, double-click to zoom in on a spot, and tap a star, planet, deep-sky object or empty sky to see what it is. Search for a constellation, bright star, Messier object or planet to fly straight to it. Layers turns on constellation borders, star patterns like the Big Dipper and Summer Triangle, a coordinate grid, the ecliptic and a red night-vision mode. Play speeds up time so you can watch the sky turn.
How accurate is it?
The Sun, Moon and planets are calculated with the Astronomy Engine library, which agrees with NASA JPL data to within about a minute of arc (the Moon is corrected for parallax for your exact location, which matters because it can shift the Moon by about a degree). Rise and set times, Moon phases and brightness come from the same library. Stars come from the Hipparcos catalogue (ESA), 15,500 stars to magnitude 7, shown at their positions for the year 2000 and turned into the sky you see with precession and nutation, so they stay correct for any date. Magnitude is a brightness scale: smaller numbers are brighter, and every 5 steps is a factor of 100. The map does not model atmospheric refraction, which lifts objects near the horizon by up to about half a degree, and it does not include comets, asteroids or satellites.
Sources: stars, constellation lines and borders, Milky Way outlines and Messier data from the d3-celestial project by Olaf Frohn (BSD-3-Clause), built on the Hipparcos catalogue (ESA) and IAU constellation boundaries. Solar-system positions from Astronomy Engine by Don Cross (MIT licence). Licence texts are in this folder.
Keep reading
Why stars twinkle but planets don’t · Proxima Centauri, the nearest star · What is the Milky Way? · Why the Moon has phases