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Re: calculate length of day as function of space at onset of fall

by CountZero (Bishop)
on Sep 26, 2016 at 19:51 UTC ( #1172663=note: print w/replies, xml ) Need Help??


in reply to calculate length of day as function of space at onset of fall

realized that fall occurs exactly when the sun sets in the west

Mmmm, that's not exactly true.

Autumn starts at the fall equinox, i.e. when the center of the sun (moving along the ecliptic) crosses the celestial equator (downward as seen from the Northern hemisphere).

That can happen at any odd moment day or night, not necessarily the moment when the sun rises or sets.

Suppose the sun crosses the equator just after midnight, then at the moment of sunset she has already travelled a little over 44 arcminutes (3/4 of a degree) along her path and the center of the sun will thus not be exactly due west when she sets.

As the angular size of the sun as seen from the earth is a little bit over half a degree, the full disk of the sun "misses" due west totally.

CountZero

A program should be light and agile, its subroutines connected like a string of pearls. The spirit and intent of the program should be retained throughout. There should be neither too little or too much, neither needless loops nor useless variables, neither lack of structure nor overwhelming rigidity." - The Tao of Programming, 4.1 - Geoffrey James

My blog: Imperial Deltronics
  • Comment on Re: calculate length of day as function of space at onset of fall

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Re^2: calculate length of day as function of space at onset of fall
by Aldebaran (Deacon) on Sep 28, 2016 at 10:38 UTC

    That can happen at any odd moment day or night, not necessarily the moment when the sun rises or sets.

    Agreed. The coincidence of the solar plane and the terrestrial plane is instantaneous, because we're supplying the coordinate system and numbers. There is a bias for when sunset is actually occuring, and I think they really are worth reading:

    Let's say you add in these biases, which frankly are in the wrong direction unless you happen to be stranded on a remote island. The act of observation requires an observer and a location, so I submit that the point in space-time where autumn occurs is where a dwarf of zero height observes the sun setting in the west, which fixes the longitude in a time-zone, ready to export to others.

    Tyrion is definitely my favorite Lannister anyways....

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