Your sky in five minutes

Skyfold computes the real sky for any place on Earth and any moment between 1800 and 2150. Everything is calculated in your browser from published astronomy algorithms; nothing is looked up online.

The workspace has three parts: the Place and Moment panel on the left, eight views in the tabs across the top (Sky, Night planner, Eclipses, Satellites, Sun & shadow, Day and night map, Cosmic odometer, Star-map poster), and a status line at the bottom that always shows the place, the local time and its offset from UTC.

Choose your place

1. Open Quick place and pick one of the example cities, or type your own coordinates into Coordinates.
2. Coordinates accepts latitude, longitude in degrees with north and east positive (for example 52.0907, 5.1214), but also degrees-minutes-seconds such as 52°05′27″N 5°07′17″E, UTM, MGRS and plus codes. Press Tab or Enter to apply.
3. Give the place a name in Place name — it appears on posters and in calendar entries.
4. Set Time zone to an IANA name such as Europe/Berlin or America/New_York. The list suggests names as you type. If your browser does not know a zone, a fixed offset such as UTC+2 works too.
5. Press Save this place to keep it in the Saved places group of Quick place.

Elevation (m) matters a little for rise and set times and a lot for eclipse contacts on mountains; sea level is fine for most uses.

Pick a moment

Use Local date and Local time, or drag Time of day to sweep through the day in five-minute steps. The four arrow buttons step one day or one hour back and forward, and Now jumps to the current time.

With the keyboard (outside text fields) you can press [ and ] for one hour, Shift+[ and Shift+] for one day, and N for now.

Read the sky chart

The Sky tab shows the whole sky above you as a round chart. The edge of the circle is the horizon and the centre is the point straight overhead. North is at the top and — because you look up — east is on the left and west on the right. Hold the chart above your head facing south and it matches the sky.

• Bigger dots are brighter stars. Move Faintest stars (magnitude) to the left in a light-polluted city (magnitude 3 to 4) and to the right under a dark sky (6 to 6.5).
• Switch Constellation lines, Constellation names, Star names, Moon and planets, Altitude grid and Star colours on and off. The key C toggles constellation lines.
• A note under the switches tells you whether the sky is actually dark: Skyfold always draws the stars, but during the day or in civil twilight you would not see them.

Find the Moon and planets

The list Above the horizon now names every planet and bright star that is up, with its height above the horizon and its compass direction, for example Jupiter · 18° south. Select an entry (or click it on the chart) to see its details: altitude and azimuth, right ascension and declination, magnitude, distance, lit fraction, and today's rise, transit and set times. For stars you also see the distance in light years and the year their light left them.

Keep your work

Skyfold saves your project in this browser as you work. File → Recent projects… lists everything saved here, File → Save file writes a .skyfold.json project file, and Edit → Undo (Ctrl+Z) takes back any change. Continue with plan a night of observing.