Solar time and clock time: when is noon?
About this app
True noon is when the shadow is shortest, and that is not at 12:00 everywhere: in Görlitz on the 15th meridian it is, in Aachen only at 12:36, in Madrid at 13:15. The noon line moves west by 4 minutes per degree of longitude. Plus sunrise and sunset over the year with standard time, the clock change or permanent summer time.
With explain mode: an AI tutor walks you through the app, points out what matters in the scene and answers your questions.
Solar time and clock time
True noon is the moment the sun stands highest, due south. A vertical stick then casts its shortest shadow. A clock, however, shows a zone time that applies to a whole country. Central European Time (CET, UTC + 1) is the mean solar time at longitude 15° East, the meridian through Görlitz. Because the Earth turns 360° in 24 hours, that is 15° per hour or 4 minutes per degree of longitude. Aachen lies about 9° further west, so noon comes 36 minutes later there, and in Madrid not until 13:15.
What you see
Three views: Noon shows the sky facing south with the sun path, a stick with its shadow, a clock and the sun height over the day. Time zone shows a noon line that moves west across the longitudes as the clock runs, and the true noon of Görlitz, Aachen and Madrid on the clock. Year shows sunrise and sunset over the whole year for always standard time, today’s clock change or always summer time. The sun position follows the NOAA approximation; the equation of time (up to 16 minutes) can be switched on.
Things to try
Drag the sun across the sky and watch when the shadow is shortest. In the time zone view set 12:00 and then 12:36: the noon line moves from Görlitz to Aachen. In the year view choose “always summer time” and 21 December: the sun would rise in Aachen only at 9:37. Then compare “always standard time” in June.
Frequently asked questions
- Why is noon not at 12:00 everywhere?
- Clock time applies to a whole time zone, while the sun follows longitude. CET matches longitude 15° East exactly. Places further west have noon later, 4 minutes per degree: Aachen at 12:36, Madrid at 13:15 (calculated without the equation of time).
- When do the clocks change in 2026 in Europe?
- Summer time began on Sunday 29 March 2026 and ends on Sunday 25 October 2026, when the clocks go back from 3:00 to 2:00 and the night is one hour longer. The European Commission proposed ending the change in 2018; the member states have not agreed so far.
- Does summer time make the days longer?
- No. How long it is light depends only on the date and the latitude. Summer time moves sunrise and sunset one hour later on the clock: evenings stay light longer, mornings stay dark longer.
- What can I change in the app?
- The place (Görlitz, Aachen, Madrid), the time, the date, the clock rule (always standard time, clock change, always summer time) and the equation of time. You can drag the sun across the sky and move through the year in the chart.
Subject: Geography & earth science
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