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Re: Unexpected USNO height correction precepts
From: Andrés Ruiz
Date: 2018 Sep 27, 13:23 +0200

Dear Antoine,

thanks for your comments. Interesting, as always.

“Opinions about publishing Planets GCL's instead of Planets GCM's in the Nautical Almanacs ?”

I prefer GCM è

For Venus 1977/03/18

· phase angle φ = 139°

· illumination = 12.09 %

· SD = 0.42 moa

The attached simulation on how Venus appears is taken from Stellarium.

So I would have been tempted to use the lower limb and correct for SD.

Easier than a phase correction.

When the illumination of the Moon is near “Full Moon”, at night the line of the horizon could be false due to the reflections. Great error.

As this case of Venus, I try to avoid these kind of weird sights.

“If you eye is sharp enough and ones can see the spot of light, or the limb it is not necessary, isn't it?”

I mean:

If you eye is sharp enough and one can see the spot of light, or the limb; the phase correction is not necessary, isn't it?

Yesterday I was cheking:

Date	UT1	Body	GHA	Dec	SD	HP	RA	Illumination	Zn	Hc
26/09/2018	18:16:17	Venus	64º 46.9'	-20º 39.5'	0.36	0.38	14:19:09	21.01	237	03º 58.67'
26/09/2018	18:16:17	Mars	331º 48.5'	-23º 10.6'	0.14	0.26	20:31:03	89.08	151	17º 56.74'
26/09/2018	18:16:17	Jupiter	50º 29.4'	-17º 20.1'	0.27	0.02	15:16:19	99.52	228	14º 49.57'
26/09/2018	18:16:17	Saturn	6º 27.0'	-22º 45.0'	0.14	0.01	18:12:29	99.75	184	23º 48.41'

My applications calculate the SD for planets and the user could choose limb = UL/C/LL. User decision…

But to be honest, when I shoot planets, I always treat them as a spot, as my eye, till now, is able to discern and interpolate the center, and no correction for SD is taken into account.

Fair winds!

Andrés Ruiz
Navigational Algorithms
http://sites.google.com/site/navigationalalgorithms/

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