Asterism: Constellation Finder

Hold your phone up to the sky and see what you are looking at. Asterism is a live star map: the phone's sensors turn the map as you move, so the stars, constellations and planets on screen line up with the night sky above you.

POINTS WHERE THE SKY REALLY IS
A sky map is only useful if it points the right way. Asterism calculates the positions of the Sun, the Moon and the planets itself, and they were checked against NASA JPL Horizons: all within 0.1°. If the Moon on screen is not where the Moon is in the sky, your phone's compass is off. Tap "Fix", put the Moon, a planet or a bright star in the crosshair, tap, and Asterism corrects the compass error. The difference between magnetic and true north (magnetic declination) is included automatically.

WHAT YOU SEE
• 8,400 stars from the Yale Bright Star Catalogue
• All 88 constellations with lines and names
• The Sun and the planets from Mercury to Neptune
• The Moon with its real phase and its real surface, based on a NASA map
• The Milky Way, drawn from NASA data
• A sky that changes color with the Sun: day, twilight, night

FIND WHAT YOU ARE LOOKING FOR
• Search: pick a star, planet or constellation and an arrow leads you to it. Planet finder and star identifier in one
• Tonight: how dark it gets, the moon phase, and which planets are up, with rise and set times
• Red light mode keeps your eyes adapted to the dark
• Limiting magnitude: hide faint stars so the map matches a bright city sky
• No compass in your phone? Drag the sky with your finger

The star map is drawn by the app and does not need the camera.

FREE, NO STRINGS
No ads. No account. Works offline, so it is ready in a field or on a mountain without signal. Your approximate location stays on your device and is only used to calculate your sky.

ASTERISM PRO
Pro is an optional subscription, weekly or yearly. The free version stays free.
• Time travel (Pro): see the sky on any date, past or future
• Camera view (Pro): the stars over your live camera image
• 110 Messier objects (Pro): galaxies, nebulae and star clusters, with a finder that guides you there

A FAIR TRIAL
The yearly plan starts with 3 days free. You get a reminder 24 hours before the trial ends, so you decide before anything is charged. Cancel any time in Google Play.

For stargazing evenings, learning the constellations, checking the moon phase before a night out, getting started in astronomy, or simply answering the question: what is that bright star?