Re: Off Topic: average daylight

From: Gerhard HOLTKAMP (
Date: Sun Jun 18 2006 - 15:31:28 EDT

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    Hi Jeff,
    >about the *difference* between the amount of sunshine,
    >twilight, and darkness at the poles and arctic circles
    >- do you suppose this has to do with the Earth's
    >aphelion and perihelion differences?
    Due to the different speed in its elliptical orbit around the sun (faster at 
    perihelion and slower at aphelion) the northern hemisphere summer is a few 
    days longer than the southern hemisphere summer. That explains the difference 
    in sunshine hours etc. between the South Pole and North Pole (and the general 
    unsymmetry between northern and southern hemisphere). But the differences 
    between the equator, arctic circle and poles need some further explanation. 
    If I take the sun as a point in the sky and leave out atmospheric refraction 
    in the sunshine calculations (in other words, if I calculate the number of 
    hours that the geometric center of the sun is higher than 0 degrees) the 
    differences become much smaller. I don't know whether the flattening of the 
    earth is also involved. Maybe somebody else has further ideas?
    When I did these calculations a few months ago I thought I understood 
    everything. But now I find my head spinning again. I'll need a few more 
    cloudy and sleepness nights to think it over!
    Gerhard HOLTKAMP
    Darmstadt, Germany
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