About
A star map that shows its working
Most sky apps will name a star for you. Few will say how they worked it out, how far off they might be, or what they are doing with your location. This one does.
What it is
A live map of the sky above wherever you say you are standing: 8,920 stars, 88 constellation figures, the Sun, the Moon and the planets, drawn for the minute on the clock rather than for a generic evening.
- Look. Drag and zoom, switch lines and boundaries on and off, set the light pollution where you live and watch the faint stars go.
- Plan. When it gets dark, when the Moon rises and how much it will ruin, what is up and how high, and how long before it sinks into the murk.
- Learn. 19 guides across 5 categories, each one moving the map while it explains, because paper does not rotate.
Why it exists
Knowing that Cassiopeia is a W will not help you find it. You also need to know which way up the W is tonight, from here, at this hour, and a static chart cannot tell you.
So this is a map to read rather than obey: the same sky an almanac would give you, from published methods, with the errors stated. Every figure on the credits page is measured, not asserted — the Moon within 8.1″ of JPL Horizons, the planets within a few arcminutes, twilight within a tenth of a second of an independent solver.
Who made it
Jesper Kiledal, as a side project. The same hands made What the Day, which teaches the Doomsday algorithm for working out the weekday of any date.
What it will not do
- Nothing follows you. There is no account to make, so your progress stays in this browser, and your location never leaves it. Privacy lists every key.
- No sky recognition from your camera. Orienting yourself is the skill.
- Not accurate enough to guide a telescope mount. Planets sit within a few arcminutes of JPL: fine for the eye, binoculars and a finder, too coarse for high power.
- No comets or asteroids, and no satellites but the station. Their element sets change faster than a static site can honestly ship; the ISS fetches fresh ones.
- Not a photograph. Colour is the catalogue's B−V index, or what the spectral class implies where B−V was never measured; size is magnitude.
If something is wrong
It might well be. The credits list the known failure modes: where the series are extrapolating, and where this app and JPL disagree on purpose. A star drawn somewhere it is not is a real bug, and worth saying so.