Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: thedoc on 21/08/2014 13:30:01
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Ed Lagniappe asked the Naked Scientists:
IF the sun never travels outside the Tropics, how does it APPEAR to be N of me at 32 deg Latitude at sunrise & sunset?
Of course, I know that the sun is not "traveling", rather the earth rotates w/ a wobble, creating the apparent "travel" of the sun across the sky, and the seasonal changes.
But it is my understanding that the sun can only be directly overhead (or N of me) if I lived between the Tropic of Capricorn & Tropic of Cancer,
YET ... it appears (in the summer) to rise & set on the horizon, N of 32° 30' 33" N
So, is there some sort of illusion, aberration, distortion or lens effect of the atmosphere at the horizon that makes the sun appear to rise & set N of my latitude?
Tropic of Cancer www.thefreedictionary.com/tropic of Cancer
n.
The parallel of latitude 23°27 N of the equator, the northern boundary of the Torrid Zone, and the most northerly latitude at which the sun can shine directly overhead.
What do you think?
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Well, it gets even more puzzling when you go further north, and once you're into the Arctic Circle you can see the sun directly to the north at "midnight", even though it gets nowhere near to being overhead at "midday". Indeed, if you stand at the pole itself in the middle of summer, you can watch the sun go right round the sky, and it's well above the horizon the whole time. How does it do that? The sun seems to have a very strange orbit round the Earth.
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Indeed, if you stand at the pole itself in the middle of summer, you can watch the sun go right round the sky, and it's well above the horizon the whole time. How does it do that? The sun seems to have a very strange orbit round the Earth.
We of course, all are aware that the earth orbits the sun. And I'm reasonably sure that David is also keen to this fact.
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Ah, I think you've cracked it - it's the Earth spinning while the Sun doesn't move, so in the middle of summer when you're standing on one of the tropic lines, the sun's directly above you at midday, but at midnight it isn't directly underneath you, but a long way to the north.
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The parallel of latitude 23°27 N of the equator, the northern boundary of the Torrid Zone, and the most northerly latitude at which the sun can shine directly overhead.
The answer is, as often, in the definition. North (or south) of the Tropics the sun is never directly overhead, just visible for substantially longer than 12 hours in summer and less in winter.
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If you're on the tropic line at 23°27 N at midday in the middle of summer (for the northern hemisphere) the sun will be directly overhead at midday, but at midnight it will be 47° north of directly underneath you. When the sun's rising and setting it will be half way in between, but if you want to measure its position precisely, bear in mind that when you see the sun (or moon) sitting on the horizon, it is only visible because of the atmosphere bending the light enough to bring it into view. Without the atmosphere it would be just out of sight, but this optical effect is small and is not the cause of the positions of sunrise and sunset being to the north of you as you stand on the tropic line.