Re: Off Topic: average daylight

From: Jeff Umbarger (
Date: Wed Jun 14 2006 - 22:49:10 EDT

  • Next message: Art Glick: "Re: Daylight"

    Hey Stephan (and Sylvia),
         First of all, be careful, the solar analemma is
    anything but symmetric! It has a larger lobe in the
    southern hemisphere and is not symmetric about the
    celestial equator. It's shape is a mixed of two
    signals; one defined by the Earth's tilt and one
    defined by the Earth's eccentricity about the Sun. But
    that said it's *shape* does not dictate *length of
    day* per se, only how soon the sun will rise or set
    with respect to a "mean sun" and the declination of
    the sun. Great explanation at:
         Does your definition of "daylight" include
    different forms of twilight (civil, nautical, or
    astronomical)? If so, than (without any mathematical
    reasoning) I would argue that the Arctic Cirles get
    the most light!
              Jeff Umbarger
              Plano, TX USA
    --- Stephan Szyman <> wrote:
    > hi there, sylvie,
    > great question!
    > at first, I was leaning toward answering that the
    > further one goes from the 
    > tropics, the fewer minutes per year of daylight one
    > will experience,  but 
    > this proved false. in their summer each polar region
    > stays in sunlight 24 
    > hours per day during the period near solstice (and
    > conversely, in darkness 
    > during the winter.)
    > if you look at an analemma (when centered on the
    > equator) you will see that 
    > it is symmetrical, and visually represents the
    > balance we are wondering 
    > about, the average amount of daylight hours for a
    > given location on the 
    > earth's surface (disregarding,  of course,
    > topographical and other 
    > obstacles! it is important to remember the earth is
    > far from being a perfect 
    > sphere.)
    > I came to the conclusion that yes, for any given
    > location on the earth's 
    > surface, the average hours of sunlight or daylight
    > annualy would be 
    > "roughly" the same.  just to be on the safe side,  I
    > called a retired 
    > physicist I know (the directory of the society's
    > observatory;) even he 
    > seemed stumped for a few minutes, but he told me
    > that he believed my 
    > analysis to be correct.
    > I will forward this question to my greatest resource
    > in these matters, the 
    > seesat-L emailing-list.
    > cheers!
    > -stephan
    > >Hey Stephan,
    > >
    > >I have a question for you and I think you are
    > probably the only person
    > >that I know who can answer it.
    > >
    > >Last night I was talking to a friend and we were
    > wondering whether the
    > >average amount of daylight hours that any given
    > location on the earth
    > >gets over the course of the year would be the same.
    > >
    > >Any thoughts?
    > >
    > >Hope all is well,
    > >Sylvie
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