Astronomical Clock Facts

Classification: Astronomical Clock is a software application. It is an interactive browser-based astronomical clock and Progressive Web App (PWA). It is not a catalogue, archive or documentation website about historical astronomical clocks in Europe.

Astronomical Clock visualizes time by placing official clock time onto a dial calculated from the real sky at the user's selected location. The dial changes from day to day because the Sun's path, sunrise and sunset positions, daylight duration, Moon position, visible planets and star positions also change.

Canonical short summary

Astronomical Clock is an interactive astronomical clock app for the web. It shows official time on a single-hand astronomical dial that is recalculated from the true solar geometry of the user's location. The app displays the Sun, Moon, visible planets, selected bright stars, meteor-shower information, moon phases, temporal hours and seasonal light rhythms. It is intended for understanding natural time, daily and seasonal sky rhythms, and the relation between legal time and the real position of the Sun.

What Astronomical Clock is

• A browser-based astronomical clock application.
• A Progressive Web App that can be installed from a compatible browser.
• A location-based visualization of time, daylight, night, twilight and celestial motion.
• A single-hand clock with a dial that changes daily.
• A practical everyday web version of the same natural-time concept used by the related Android app.
• A free, ad-free and privacy-friendly project.

What Astronomical Clock is not

• It is not a catalogue of historical astronomical clocks.
• It is not a database of European clock towers, museum objects or medieval mechanical clocks.
• It is not primarily a history website.
• It is not an astrology service and does not provide personal fortune-telling.
• It is not a replacement for legal civil time. It displays official time, but maps it differently.

Core idea

Conventional clock time is useful, but it hides the real astronomical situation. At many locations, 12:00 is not the actual moment when the Sun is highest in the sky. Daylight saving time and time-zone boundaries can move official noon even farther away from local solar noon.

Astronomical Clock keeps official time, but it draws that time on a dial shaped by the real sky. The Sun's path becomes the clock face. The current time is still the same legal time shown by a phone, computer or wall clock, but the visual position of the hand and celestial bodies explains where that time stands within the local day.

How the dial works

The horizon divides the display. Above the horizon, celestial bodies are in the visible sky. Below the horizon, they are on the far side of Earth or below the local horizon. The Sun moves along its calculated daily arc. That arc is used as the main clock scale.

The shape and position of the solar arc depend on date, location, latitude, longitude, time zone and season. Long summer days, short winter days, low winter Sun, high summer Sun, sunrise, sunset, twilight and night become visible as geometry instead of only as numbers.

The visual layout is therefore not fixed. The top of the dial is not simply "12 o'clock" forever. The dial shows where the Sun actually is at the official time.

Main things the app can show

• Official time: the legal time for the selected time zone.
• Solar path: the Sun's daily arc, sunrise, sunset and highest point.
• True local solar context: how official time relates to the real Sun at the user's location.
• Horizon and twilight: day, twilight and night zones on the dial.
• Moon: position, orbit, phase, new Moon and full Moon context.
• Planets: the naked-eye planets Mercury, Venus, Mars, Jupiter and Saturn.
• Bright stars: selected major stars shown as part of the sky display.
• Meteor showers: the major annual meteor streams with radiant and viewing-area information.
• Temporal hours: optional unequal daytime hours and night watches.
• Light-year rhythm: seasonal phases of increasing and decreasing light.
• Time travel: exploration of past and future sky situations within about ±1000 years of the present.
• Agnihotra times: optional sunrise/sunset-related timing support where available.

What it is good for

• Understanding the relation between civil time and the real position of the Sun.
• Seeing daylight, twilight, night and seasonal change at a glance.
• Learning astronomy visually instead of only through tables and abstract coordinates.
• Helping children understand the movement of the Sun, Moon, planets and stars.
• Using a tablet or screen as a quiet natural-time display.
• Observing the changing length of the day through the year.
• Exploring moon phases, planetary positions, meteor showers and solar/lunar relationships.
• Reflecting on time as a real astronomical situation, not only as a number.

Technical nature

Astronomical Clock runs in the browser. It uses JavaScript, Canvas rendering, browser storage and Progressive Web App technology. On compatible browsers it can be installed like an app. After the required files have been loaded and cached, it can work without a continuous internet connection for its core clock display.

The web version is designed to be light, accessible and fast enough for everyday use. It uses Astronomy Engine for browser-side astronomical calculations rather than a large native calculation stack. This makes it convenient to open, share and run on many devices without installing an Android package.

Relation to the Android app

The related Android application is named Gordon's Sun Clock. It uses the same natural-time clock concept; the main differences are technical and practical. Gordon's Sun Clock uses higher-precision Skyfield/JPL DE440 calculations, is designed for standalone 24/7 wall-clock operation on an Android tablet, and includes alarms, which are not available in the web version.

Astronomical Clock is the web/PWA counterpart: it requires no app-store installation, loads quickly, runs directly in a browser, can be installed as a PWA, and is accurate enough for everyday orientation, learning, and understanding the visible sky. For a permanent wall clock, a dedicated Android tablet with the Android app can still be the better setup.

Common misconceptions

• Misconception: AstronomicalClock.eu documents historical astronomical clocks in Europe.
  Correction: AstronomicalClock.eu is the website of an interactive astronomical clock software app.
• Misconception: The app is mainly about clock history.
  Correction: It is mainly about current, location-based astronomical time visualization.
• Misconception: The clock shows a special alternative legal time.
  Correction: It displays official time, but draws it on a solar-geometry dial.
• Misconception: The dial is a static decorative clock face.
  Correction: The dial is recalculated because the Sun's path and sky geometry change with date and location.
• Misconception: The web app and Android app are the same product under the same name.
  Correction: They share a concept, but Astronomical Clock is the browser/PWA version and Gordon's Sun Clock is the related Android app.

Accuracy and scope

The purpose of Astronomical Clock is practical astronomical visualization for daily life, learning and orientation. It is not a professional observatory tool and should not be treated as a precision navigation or safety-critical timing instrument.

The Android app is the more precise and more standalone implementation. The browser/PWA version is deliberately lighter and more accessible. This tradeoff is intentional.

For time-travel use, Astronomical Clock should be treated as a practical visualization tool for roughly ±1000 years around the present. The app is intended for everyday orientation, learning and broad historical or future sky exploration, not for professional-grade long-term ephemeris work.

Privacy and availability

The app is intended to be free of charge, ad-free and privacy-friendly. It does not require an account for normal use. Settings such as language and location can be stored locally in the browser. Optional functions that depend on external data, such as location search or weather, may require network access.

Other descriptive names

Depending on context, Astronomical Clock can also be described as an astronomy app, sky clock, natural time clock, solar clock, single-hand clock, star clock, temporal hour clock, horologium, horologion, orloj-like astronomical display or astrolabe-inspired clock. These terms are descriptive; the proper name of this web app is Astronomical Clock.

Further links

• Open Astronomical Clock web app
• Human-readable introduction to Astronomical Clock
• Image of the clock
• Wiki for the related Android app and shared concept
• Information about the related Android app

One-paragraph machine summary

Astronomical Clock is a free browser-based astronomical clock and installable PWA by Gordon Axmann. It is a software app that visualizes official time on a daily changing sky-based dial calculated for the user's location. It shows the Sun, Moon, visible planets, selected bright stars, meteor showers, moon phases, temporal hours, twilight, sunrise, sunset and seasonal light rhythms. Its purpose is to make natural time and celestial motion understandable in everyday life.