NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Moon sight?
From: Gary LaPook
Date: 2014 Oct 4, 00:45 -0700
From: Gary LaPook <NoReply_LaPook@fer3.com>
To: garylapook@pacbell.net
Sent: Saturday, October 4, 2014 8:26 AM
Subject: [NavList] Re: Moon sight?
From: Samuel L <NoReply_SIamuelL@fer3.com>
To: garylapook---.net
Sent: Saturday, October 4, 2014 5:06 AM
Subject: [NavList] Moon sight?
From: Gary LaPook
Date: 2014 Oct 4, 00:45 -0700
I've pointed this out before that using the correction tables in the N.A. can be confusing for a person learning celestial navigation because it is not clear where the values come from and what is included in them. i recommend that students use the correction tables from the Air Almanac which are all separate. Doing the same correction with the Air Almanac tables it goes like this (all values are tabulated to whole minutes)
Hs = 31°02'
Ref - 2'
S.D. + 16'
P in A +
50'
-------------------------
Ho = 32°06'
The slight difference is due to the tabulations being rounded to
whole minutes.
gl
From: Gary LaPook <NoReply_LaPook@fer3.com>
To: garylapook@pacbell.net
Sent: Saturday, October 4, 2014 8:26 AM
Subject: [NavList] Re: Moon sight?
I don't know where you got your correction values from.
First. you labeled the first correction as "IE" which means Index error. You show a negative value for the index error so you must reverse the sign of IE to apply it to the sextant reading but
you subtracted it from the sextant altitude. Did you mean to label it as "IC," index correction, which is the IE with the sign already reversed and applied as is to the sextant altitude?
Assuming the latter, then you applied it correctly and determined Ha of 31°01.9'.
But the rest of you computation is quite wrong. Looking at the moon correction table for 31° 01.9' you find the main correction is +58.5' not the +47.4' that you used which would be the correction for an Ha of 49° 20', not for 31°01.9'. Then going down the same column of the correction table you find the lower limb correction of + 6.8' (by interpolation) for the HP of 59.3', not the + 5.9' that you used. So doing the corrections correctly:
31°01.9'
+ 58.5'
+ 6.8'
-----------
32°07.2'
That is all there is to it, you do NOT apply refraction or semi-diameter as these are already included in the corrections
The only reason that your calculation came close is that you applied these errors and they cancelled out your other errors.
gl.
From: Samuel L <NoReply_SIamuelL@fer3.com>
To: garylapook---.net
Sent: Saturday, October 4, 2014 5:06 AM
Subject: [NavList] Moon sight?
I took my first sight on the Moon last night (10/3/14) at 00:26:20 GMT.
In working through the sight reduction all went reasonably well except when it came to the sextant correction
work.
The Moon's HP was 59.3
Here's what I did;
HS- 62d 3.9min
IE
-0.1min
Ha divided by 2 (since using an AH) 31d 1min 54sec
Main correction= +47.4min
Lower Limb= +5.9min
Refraction= -1.7min
Moon's SD= +16.3min
Ho= 32d 9.8min
Are there any other corrections that are to be applied that I've not included here?
The resulting LOP gets me within about 2 miles of the Ap Longitude (W 075d 45.6min)
Thank you,
Sam
