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(1) For various latitudes, the following table shows the hours the sun is up over the course of one year:
90 4443.88
75 4566.94
60 4511.63
45 4459.29
30 4438.84
15 4427.73
0 4421.12
-15 4417.46
-30 4416.59
-45 4420.09
-60 4439.36
-75 4409.84
-90 4322.13
The sun is up more time in mid latitudes north and south than at either the equator or the pole, but also more time in the northern than in the southern hemisphere. The latter difference is the result of the sun being north of the equator for more time than south, because the earth is farther from the sun in northern summer and therefore moving more slowly in its orbit. Overall, the sun is up over half the time as atmospheric refraction raises the apparent sun near the horizon, and also the sun is considered up when any part of the solar disk is above the horizon. That effect also causes the mid-latitude excess, as those latitudes benefit from a prolonged daily slantwise passage of the sun through the horizon.
(2) For various latitudes the following is the integrated amount of insolation over the course of a year. The units are arbitrary, rather than calories per square centimeter per year or the like, but are in proportion to the amount received:
90 2626
75 2827
60 3599
45 4674
30 5561
15 6132
0 6327
-15 6132
-30 5561
-45 4674
-60 3599
-75 2828
-90 2627
The poles suffer from the fact that the sun is lower on the horizon there even when it is up. Also, while the sun is closer during southern hemisphere summer, summer lasts longer in the northern hemisphere, as mentioned above.
For more details see http://www.wiskit.com/marilyn/sunshine.html. The item had originally appeared, ambiguously worded without a clarification as to which meaning was meant, in Marilyn vos Savant's Parade column. Marilyn had answered that the sun shone over every part of the world for exactly half the time during the year, either for 6 months straight as at the poles or 12 hours every day as at the equator or some compensation of summer vs. winter elsewhere. This ignores the eccentricity of the earth’s orbit that causes the sun to be north of the equator more than south, and the raising of the low sun by atmospheric refraction. The above URL is in the Marilyn is Wrong web site. |
