A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Frank Reed
Date: 2014 Oct 17, 10:00 -0700
Robert, you wrote:
"I am guessing people will suggest a linear fit."
Yes. That won't be far off, since it's such a small difference anyway. Start at 16.3 in January, and subtract 0.1 per month through July. Then add 0.1 per month starting in August until back to 16.3 in January. That's fairly close. For what it's worth, I usually 'calculate' this graphically. I know that the variation is closely approximated by a simple sine curve. The average value is 16.0. The amplitude of the curve is 0.27'. And the peak is at January 4. Those individual items seem easier to remember than a formula. But if I have a small page or table to store info, then I think I might prefer the formula. On the other "other hand", a table of values once a month would be nearly as compact and quicker.