What is solar noon?
Solar noon is when the sun is at its highest point in the sky each day. It occurs when the Sun crosses the celestial meridian (an imaginary line running across the sky from due South to due North, passing through a point directly overhead (the zenith)).
At solar noon, the Sun is due south in the Northern Hemisphere, and due north in the Southern Hemisphere. The Sun is directly overhead (at the zenith) at solar noon at the equator on the equinoxes; at Tropic of Cancer (latitude 23½°N) on the summer solstice in June; and at Tropic of Capricorn (23½°S) on the winter solstice in December.
Why is this important?
The Sun casts its shortest shadow when it is at its highest point of the day. You now know that this moment in time is called solar noon. We will use the length of a shadow to figure out how high the Sun is above the horizon. By comparing the angle of the Sun from two locations, we can estimate the Earth's circumference, much like Eratosthanes did over 2,000 years ago.
How do I determine solar noon for my location?
You will need three pieces of information:
- The Latitude and Longitude of your observing location
- The dates when you will be making measurements
- Your local time zone (including daylight savings time / summer time)
Once you have gathered this information, use NOAA's Sunrise/Sunset/Solar Noon Calculator to determine the time of solar noon. Be sure to pay close attention to your time zone, as daylight savings time (summer time) changes the time of solar noon.