NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Frank Reed
Date: 2024 May 10, 09:37 -0700
We can measure the angular size of the sunspot group by sextant or estimate it from that photo. There are subjective choices here since sunspot groups, by their nature, have fuzzy edges. Once we have the size in minutes of arc (m.o.a.), then it's the same math we can use to estimate the distance to a ship if we know its length and measure its angular size:
m.o.a./3438 = size/distance
where size and distance would, of course, both be in the same units (both in miles, e.g.). You need to look up (or know) the distance to the Sun: 93 million miles or 149 million km. Key point: no trig needed! If you find smoke coming out of your ears, and you're saying to yourself, "error... error... trigonometry must be applied... trigonometry... must...", then you are a robot. ;) For any angles smaller than a few degrees, setting up a triangle and delicately applying the trig "rules" that you learned in school... is all wasted effort. See the attached image for this specific case.
Frank Reed
