Solar noon

What does Solar noon mean?

Solar noon is a position of the sun rather than a time on a clock. It falls midway between sunrise and sunset, and it is computed from a date and a set of coordinates instead of measured from the sky, so weather does not move it. It lands on 12:00 only by coincidence. Clock time runs in wide zones and jumps an hour for daylight saving. Solar noon comes earlier at the eastern edge of a time zone than at the western edge, and its arrival drifts across the year as Earth's tilt and elliptical orbit change how fast the sun appears to cross the sky. The moment is worth naming because sun height, not the hour and not how bright the day looks, sets the shortest path sunlight takes through the atmosphere that day. That path is also the gate on the ultraviolet band skin uses to make vitamin D, since a low sun sends those wavelengths through more ozone, which absorbs them. That is geometry, and it is also why the day's ultraviolet peak sits near solar noon rather than at 12:00 on the clock, which makes the hours on either side of it the gentler ones. Ultraviolet radiation is a carcinogen and the most preventable cause of skin cancer, so the hours around the peak are the ones to cover up in, and correct sunscreen use does not prevent vitamin D synthesis while it does prevent burning.

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