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## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

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Re-doing my homework (by Bygrave)
From: Tony Oz
Date: 2017 Feb 22, 16:41 -0800

Hello!

I'm re-doing these sights now by Bygrave (for now - with Casio).

Can't for the life of me find where my error is. Here is the record:

Given:

2016-10-31T10:11:36UTC

LatAP = 37°15'N; LonAP = 66°30'W

Regulus: Dec = 11°53'N, GHA = 40°44'

Solution:

LHA = GHA + LonAP = 334°14'

H = 360° - LHA = 25°46'; H is OK, no rule apply.

CoLat = 90° - 37°15' = 52°45'

W = tan-1(tan(Dec)/cos(H)) =  tan-1(tan(11°53')/cos(25°46') = 13°9'

since the names are same and LHA is 334° - the W should be added.

X = 52°45' + 13°9' = 65°54'; X is OK, no rule apply.

since X < 90° -> the Y = X == 65°54'; Y is OK, no rule apply.

Az = tan-1(tan(H)·cos(W)/cos(Y)) =  tan-1(tan(25°46')·cos(13°9')/cos(65°54')) = 49°1'

since Lat is North, X < 90° and LHA = 334°, then

Zn = 180 - Az = 130°59'

Hc =  tan-1(cos(Az)/tan(Y)) = tan-1( cos(49°1')/tan(65°54')) = 16°21'

I compare the results with the Ageton's and the Cosine Law on calculator: Zn is OK but Hc is wrong. And what puzzles me - it is only Regulus's Hc is wrong, all other bodies calculate OK with Bygrave.

I'm lost...

Regards,

Tony

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