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Subject: Re: additional planet corrections...
From: Chuck Taylor (ctaylor@XXX.XXX)
Date: Tue Nov 23 1999 - 18:50:05 EST
On Tue, 23 Nov 1999, Russell Sher wrote:
> Does anyone know why the additional altitude corrections in the nautical
> almanac are needed for Venus and Mars at certain times of the year? Is this
> for refraction?
Russell,
Mostly for parallax. The Sun, Moon, Venus, and Mars are the only bodies
close enough to earth for parallax to be a factor. Parallax for the Moon
is treated separately. For the Sun, there is about 0.1' built into the
main correction for altitudes up to 60 degrees. In the cases of Venus and
Mars, whether or not we are close enough depends on whether we are on the
same side of the Sun or opposite sides of the Sun (which depends on time
of year). If on opposite sides, the distance is too far for parallax to
matter. Jupiter, Saturn, and the stars are always too far away for
parallax to matter.
Cheers,
Chuck
----------------
Chuck Taylor
SEASCAPE GB 32-2
Everett, WA, USA
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