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From: Bill (no email)
Date: Thu Dec 08 2005 - 18:34:38 EST
> The Nautical Almanac incorporates corrections for Venus' phases, so
> if you use their ephemerides, etc, in your calculations, you should
> be fine. Perhaps you ought to tell us why you're interested in the
> diameter of Venus.
Fred
I am aware of the almanac corrections, but those are for altitude (up from
the horizon).
When shooting lunars with Venus recently, Venus can range from the same
altitude as the moon to lower than the moon, so altitude corrections may not
apply as the moon-as-horizon would split a different "side" of the partially
illuminated sphere than a true horizon.
If Frank's program does not take phase into account for Venus and I am
splitting a body that has an apparent width of 10" instead of 40" (right
side illuminated?), then my observation would be 15" off.
As we move towards inferior conjunction Jan 13, Venus may become 60" or more
in diameter, with the area illuminated diminishing. If not accounted for
one way or another, we could be looking at an errors up to 1.0'.
So apparent diameter, amount illuminated, and the angle of the illuminated
portion would appear, IMHO, to be of concern.
Bill
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