Subscribe Edible San Diego
Published by Katie Stokes
I was once asked to look up the days in the year in which the sun was at 50 degrees or more above the horizon here in San Diego. It was an interesting question. I eventually found a website which showed the angle of the sun during the day for each day of the year. The data was in text format and only displayed for a given date. I designed a graphical way of displaying the information and laboriously worked through the data to produce the data in the way I envisioned it.
Apparently the sun needs to be at 50 degrees or higher for UVB (Ultraviolet B) sunlight rays to penetrate the atmosphere. UVB sunlight is the sunlight which gives the human body vitamin D.
In this chart, the vertical 5 day intervals lines represent the 1, 6, 11, 16, 21 and 26 day marks for each month. All times are Standard Time. Interestingly, the latest sunrise is well after winter solstice while the earliest sunset is well before winter solstice. The earliest sunrise is well before summer solstice and the latest sunset is well after summer solstice. The shortest sunshine day is at winter solstice and the longest sunshine day is at summer solstice.
The sun is at 50 degrees or higher for UVB in San Diego starting about March 1 at noon, increasing to about six hours at Summer Solstice, then ending around October 11.
The Sun Angle Chart for San Diego, by John S. Stokes III, may be freely copied with attribution. Source data was from http://aa.usno.navy.mil/data/docs/AltAz.php (link no longer working).