A good sunrise/sunset program will take into account both refraction and the
diameter of the sun. The point I was making is on the day of the equinox,
at least part of the sun should be visible for 12 hours and 6 minutes.
That's two extra minutes on each side for refraction and 1 extra miniute on
each side for the diameter of the sun.
Carl Moreschi N4PY
Franklinton, North Carolina
n4py@earthlink.net
----- Original Message -----
From: "Jim Reid" <jimr.reid@verizon.net>
To: "Carl Moreschi" <n4py@earthlink.net>; <tentec@contesting.com>
Sent: Saturday, March 15, 2003 7:57 PM
Subject: Re: [TenTec] Equinox Day
> Carl, N4PY, wrote:
>
>
> > The refraction of the Earth's atmosphere increases the
> > amount of daylight by about 2 minutes at sunset and about
> > 2 minutes at sunrise for latitudes below about 40 degrees.
> > Add to that another minute for the diameter of the sun on
> > each end and you have a total of 6 minutes added to daylight.
>
> Do programs, such as my GeoClock, account for that refraction,
> or do they just calculate based upon the geo center of the
> Sun's actual disk, or the "apparent" disk as caused by this
> refraction? I recall this came up once before, when the
> program reported, at equinox, that the Sun's center would
> be on the horizon at both the North and South poles. Because
> of refraction, it was said then, that the Sun would never be
> seen simultaneously at both poles (nor any part of the Sun
> simultaneously, hi).
>
> > But the true equinox is the same everywhere on the earth
> > and that occurs the instant the center of the sun passes
> > through the plane of the Earth's equator. This is 0100 GMT
> > on March 21 this year.
>
> I guess that is the true "definition" of equinox, but we will not
> have equal hours of sun up and sun down that day here. I'll
> have to remember to look to see what the sunrise and
> sunset times are here on the 21st.
>
> Something else to do until an Orion is shipped out here!
>
> Do you suppose my GeoClock (V8.4) knows about the refraction?
> That program is the source of my trivia info about this day, hi.
>
> 73, Jim KH7M
>
>
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