asterism

What is this?

Upload a photo of the night sky and asterism tells you what you were looking at: it names the stars, draws the constellations, and marks the Moon and planets in your frame.

It works out where your camera was pointing from the star pattern alone — no location, no compass, no account.

Works best with an ordinary phone photo of the night sky. Handheld and a little hazy is fine; the more stars you can see, the better it does.

Taking a photo the solver can read

The solver needs stars in the pixels, not just in the sky. A few seconds of exposure makes more difference than anything else.

• Use night mode. iPhone: Night mode comes on by itself in the dark (the yellow moon icon) — tap it and drag the slider to the longest time it offers. Pixel: Night Sight, which switches to Astrophotography on its own once the phone is still. Samsung: Night mode.
• Hold still — any way you can. A tripod is ideal, but a phone leaned against a wall, laid flat on a car roof, wedged in a shoe, or pressed into a beanbag or a bag of rice works too. Use the timer or a volume button so the tap doesn't shake it.
• Zoom out, not in. The main lens or the ultrawide, with no digital zoom: more sky in the frame means more stars to match.
• Get away from lights. A streetlight in the frame flattens the sky. Haze, suburbs, and a bit of glow are fine — a dark sky helps, but the long exposure matters more.
• Mind the Moon and the clouds. A bright Moon or thin cloud washes out everything fainter. Another hour, or another night.
• Upload the original. Screenshots, edits, and photos passed through a messaging app lose the camera's notes about when and how the shot was taken — the solver uses those to explain what it sees.