I’m looking for a non-mechanical way to determine (guesstimate) how long it will take the sun to move from its current position to another position. Given that the sun moves 1 degree every 4 minutes, what can I use to estimate the number of degrees that the sun needs to move?
For example, I’m going to a high school baseball game and the sun is n degrees over a shade tree. What is a handy, rule of thumb kind of method for determining how long until the sun is behind the tree? I know it’s n*4 but I don’t have a quick and dirty way of determining n.
Suggestions? (Other than getting a hobby and/or life. And no, I won’t buy a sextant. )
You seem to be asking how to do simple math without using any math. If you want a simple way to estimate I suggest you start by learning the diameter of the sun. Not absolute diameter but apparent diameter which is about one half degree so it’s going to take about two minutes to move one full diameter. Armed with this knowledge and some eye protection such as a #10 welding lens you can estimate how long the sun will take to move somewhere by judging how many diameters it has to move. Sorry if that is too mechanical for you.
That’s exactly what I’m asking, that’s what a “rule of thumb” is, isn’t it? I was hoping more for something like “The width of the average hand held at arm’s length will subtend an angle of n degrees” blah blah blah. I did not know that the sun occupied half a degree so that’s a good start.
If you mean a rule of thumb for measuring angles: with your arm outstretched, the width of your fist is roughly 10 degrees. So it takes about 40 minutes for the sun to move that far. Does that help?
Also take into account that, unless you are at or near the equator, the sun does not rise and set vertically, but at a diagonal. The farther you are from the equator, the more diagonal the ascent/descent (shallower angle as you move north or south from the equator).
A fist at arms length subtends about 10 degrees, an open hand about 20°.
It’ll take the sun about 40 minutes to cross your fist, and 80 to cross an open hand.
I think the Sun and the Moon are both half a degree in size, so you could use them to calibrate your extremities. My little finger is also that angular size at arm’s length, for instance.
I’ve never worked this out but isn’t the rate of rise and setting of the sun proportional to the sine function? I believe that the rate of movement is slowest when it’s at the apex and fastest at sunrise and sunset. Then again I could be all wet. I’ll have to go and do some geometry.
Yup, that’s the answer. Except for the increasing effect of atmospheric refraction as they near the horizon, the sun and moon both move at a stately 1/4° per minute regardless of the time of day.
That refraction near the horizon is pretty small potatoes, as it only raises the image of the setting sun or moon by about 1/2 a degree.
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