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    Re: Speed of Sunset
    From: David Pike
    Date: 2016 Oct 2, 04:56 -0700

    Herbert,

    Why do you keep insisting that nothing changes at lat = 0, when even your own data clearly shows a change of 4 minutes for the entire twilight of 44 minutes!! That is 9%, (which is, surprise, surprise!) equal to 1 / cos(23.4deg),  

    I think I can see where you get the 1/cos23.4 from.  At the Equinox at 0N the Sun rises vertically on 090; goes straight over your head; sets vertically on 270; and crosses the twilight zone in time‘t’.  At the Solstice it sets crossing the vertical at 23.4 degrees (I’ve still got to check this).  Then the duration of twilight will be t/cos23.4 or 1.09t.  Can you ‘magic’ this to get a similar expression when latitude is 45 or 50N? DaveP

       
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