Astronomical Sun Clock (AstrClck)
Natural Time: A single-hand clock with a daily-changing dial – aligned with the rhythms of celestial bodies and nature
Why Astronomical Sun Clock?
Ordinary clocks show official time on a fixed dial. Astronomical Sun Clock shows the same official time, but maps it each day onto the actual solar path at your location. This makes it visible when the sun is highest, when it rises and sets, and how much daylight remains.
The dial therefore follows the real geometry of the sky without replacing official time. Sun, horizon and hour marks together form a clock that changes with location and season.
What do you see?
The horizon divides the screen. Above it: the sky with sun, moon, planets, and the ten brightest stars. Below: celestial bodies on the other side of Earth. The sun travels throughout the day from left (east) to right (west) along its path, just like in the real sky (reversed in Southern Hemisphere). The moon has its own orbit. Planets and stars show their positions.
The sun’s path functions as a clock face: hour marks place official time along that path. At a glance, you see how long the day is, when night falls, and how this changes with the seasons.
What is Astronomical Sun Clock for?
- Reconnection to natural rhythms – not just daily, but seasonally
- Children intuitively understand the movements of stars and celestial bodies
- Wall clock: Hang it on the wall and observe the natural change of time daily
- Astronomy: Observe conditions for solar eclipses, full/new moons, and planetary positions
Special features
- Location-dependent: Works worldwide with your coordinates
- Offline: No internet connection needed after initial setup
- Time travel: Explore past and future – even the sky at your birth
- Meteor showers: The eight major showers with viewing area and radiant
- Optional second-precise Agnihotra times with countdown
- Optional weather display with a calm, icon-based daily overview
- Temporal hours display: 12 unequal daytime hours & 4 night watches – historical time system
Seven years of experience
I’ve lived with this clock for seven years. It taught me to connect more with natural rhythms. The changing paths of sun and moon show me how short winter days are, how lunar phases work, etc. I recognise the angle of sunlight and see the starry sky.
This app is my gift to the world. Free, ad-free and privacy-friendly.
Two versions
Gordon’s Sun Clock comes in two versions: The Astronomical Sun Clock (AstrClck) is the lightweight version. It runs as a web app/PWA in the browser and as an Android app of about 2 MB, starts quickly and allows you to adjust the time live.
Gordon’s Sun Clock JPL is the JPL version for Android. It uses Skyfield with JPL DE440 ephemerides, starts and calculates more slowly, but provides sub-second accuracy and GPS time synchronisation.
Web app – Astronomical Sun Clock (AstrClck) >
Play Store – Astronomical Sun Clock (AstrClck) >
Play Store – Gordon’s Sun Clock JPL >
GitHub – AstrClck / Astronomical Sun Clock >
Setup >
Explanation of the clock face >
More information >
Support >
Automatic translation into more languages >