What is solar noon?
Solar noon is when the sun reaches its highest point. Here is why that is almost never at 12:00 on your clock, and how to work out when it happens.
Solar noon is the moment when the sun crosses your local meridian: the imaginary line in the sky running from due north, through the point straight overhead, to due south. At that moment the sun is at its highest point of the day, shadows are shortest, and the sun is exactly due south (seen from the Northern Hemisphere outside the tropics) or due north (in the Southern Hemisphere).
It sounds as if solar noon should be at 12:00. In practice it almost never is.
Three things that move solar noon
1. Your position in the time zone
The Earth turns 15° every hour, so the sun passes over places further west 4 minutes later for every degree of longitude. A time zone, however, shares one clock time across many degrees of longitude. Central European Time is based on the 15° east meridian; Ljubljana is at 14.5° east, so the sun passes about 2 minutes after it would at 15°. Madrid, on the same clock, is at 3.7° west, almost 19° further west, so its solar noon is about 75 minutes later.
2. Daylight saving time
When clocks go forward in spring, everything the sun does happens an hour later on the clock. In summer, solar noon in most of Europe and North America falls between about 12:45 and 14:30.
3. The equation of time
Even at a fixed place, solar noon drifts through the year by about half an hour in total, because the real sun does not move across the sky at a perfectly even pace. It is up to about 14 minutes “slow” in February and up to about 16 minutes “fast” in early November. This drift is called the equation of time.
A worked example
Ljubljana is at 14.51° E, in Central European Time (meridian 15° E).
- Longitude correction: 4 min × (15 − 14.51) = about +2 minutes.
- On 11 February the equation of time is about −14 minutes, so solar noon is around 12:00 + 2 + 14 = 12:16.
- On 3 November it is about +16 minutes, so solar noon is around 12:00 + 2 − 16 = 11:46.
- On 21 June (daylight saving time, equation of time about −2 minutes), solar noon is around 13:00 + 2 + 2 = 13:04.
The solar noon calculator does this for any place and date, and shows the full yearly curve.
What solar noon is good for
- Finding true north. At solar noon a vertical stick’s shadow points exactly north in the Northern Hemisphere (outside the tropics). This is more reliable than a magnetic compass, which points to magnetic north.
- Sun and shade. The sun is highest at solar noon, so this is when it reaches furthest into courtyards and between buildings, and when UV radiation is strongest.
- Solar panels. A south-facing panel receives the most direct light around solar noon, not at 12:00. If your panels produce their peak at 13:15 in summer, that is solar noon, not a fault.
- Understanding sunrise and sunset. Solar noon is (almost exactly) halfway between them. If you know solar noon and the day length, you know both.
Frequently asked questions
What is solar noon?
Solar noon is the moment when the sun crosses the local meridian, the imaginary north-south line through the sky above you. At that moment the sun is at its highest point of the day and exactly due south (in the Northern Hemisphere outside the tropics) or due north (in the Southern Hemisphere).
Why is solar noon not at 12:00?
Clock time is shared by a whole time zone, but the sun passes each place at a slightly different moment. On top of that, daylight saving time shifts clocks by an hour, and the equation of time makes solar noon drift by up to about 16 minutes through the year.
Is solar noon exactly halfway between sunrise and sunset?
Almost exactly. The difference is usually a few seconds and comes from the sun's changing declination during the day.
When are shadows shortest?
At solar noon. That is why solar noon is useful for finding true north: at that moment shadows point exactly north (or south in the Southern Hemisphere).