// ~/sextant
Sextant
A night sky and satellite tracker for iPhone. Hold it up and it shows what's there: stars, planets, the Moon in its phase, and the satellite crossing overhead right now, with a fading trail so you can tell which dot is which.
$ cat features.txt
- Point mode. Aim the phone; the sky follows. Pick something and an arrow walks you to it.
- Satellites. Thousands, from CelesTrak's orbits, with trails, brightness, and a countdown to when each one fades into Earth's shadow or sets.
- Visible tonight. What's worth looking at between dusk and dawn, an altitude chart for each, and the satellite passes you can actually see.
- Comets and meteor showers. Comets from the Minor Planet Center's orbits, and all 37 showers on the IMO calendar, with the nights they peak.
- Time travel. Drag the clock to see tonight at 3 a.m., or next week.
- Night mode. Everything in dim red, so the screen doesn't undo your dark-adapted eyes.
- No account, no ads, no tracking. It works offline from the orbits it last downloaded.
$ cat faq.txt
- A satellite faded out halfway across. Did I lose it?
- It went into Earth's shadow. Satellites shine by reflected sunlight, so they're visible after dusk and before dawn, when it's dark where you are but still sunny up there. Select one and tap its name: the card counts down to when it goes dark.
- Why does it want my location?
- The sky depends on where you stand. Your location is used on the phone to work out what's overhead and is never sent anywhere. Without it, Sextant uses the main city of your time zone, which is close enough for the stars but not for satellite passes.
- The top bar says the satellite data is days old.
- Orbits come from CelesTrak and are refreshed about twice a day when you have a connection. A few days old is fine; after two weeks the satellites are hidden rather than drawn in the wrong place.
- How accurate is it?
- Star and planet positions are tested against Stellarium to under half an arcminute, satellites and pass times against Skyfield to under a second. The weak link is how old the orbits are, so stay connected now and then.
$ mail # bugs, ideas, "what was that thing I saw"
support@ducktyping.dev · privacy policy
$ cat CREDITS
Positions by Astronomy Engine (Don Cross, MIT). Stars from the HYG database (David Nash, CC BY-SA 4.0). Milky Way from ESO/S. Brunier (CC BY 4.0). Constellations from d3-celestial (Olaf Frohn, BSD). Orbits propagated with SatelliteKit (Gavin Eadie, MIT) from CelesTrak data (Dr. T.S. Kelso).