Line of Position - Moon: Find computed azimuth / Zn & intercept

Professional Mariner Forum
1

I have gone over the two moon problems (yes I know since there are only two and who really gives a crap), but I can’t figure out where I’m going wrong.

Page 34 Deck Officer Study Guide, Book 5 Navigation Problems

050259/NP02165

On 25 Feb, at 0622 ZT, you observe the upper limb of the Moon with a sextant altitude of 59 58.6’. Your DR psn is Lat 30 28.3’ S, Long 102 39.3’ E. Chronometer reads: 11h 21m 18s and is 48s slow. HOE: 59’, IE is 2.5’ on the arc. What is Zn and intercept of the sight using the AP?

Here is what I keep getting for my numbers:

LHA moon = GHA moon + Long = 282 32.3’ + 102 32.3 E = 24
Lat = 30 S
Dec = S 10 56.1

Ho = 60 00.4
Hc = 60 39.0
Zn = 305.4 (this is the only number I get right)

Can someone explain what I’m doing wrong with my Ho and Hc? Thank you

2

you need to subtract on the arc corrections and height

3

[LEFT][SIZE=3]H<SUB>S: 59 <SUP>o 58.6 ’
IE: - 2.5 ’
HS: 59 o 56.1 ’
Dip 59 ’: - 7.5 ’
AltApp: 59 o 48.6 ’
UL Corn:- 30.0 ’
AltApp: 59 o 18.6 ’
Alt Corn: 39.0 ’
AltApp: 59 o 57.6 ’
HP Corn:+ 2.7 ’
HO: 60 o 00.3 ’ T
HC: 59 o 56.2 ’ C
[B][FONT=PNMAEM+TimesNewRoman,Bold,Times New Roman][SIZE=3]Intercept: 04.1 ’ Towards [/SIZE][/FONT][/B][/LEFT]
Remember C.G.A. (Computed greater, Away!)
</SUP></SUB>[/SIZE]

4

Your assumed position doesn’t look right…Wouldn’t it be 102 27.7 E since you will be adding it… which would give you an LHA of 25??

5

Nice. So I got my Ho correct. How did you get Hc? Are my entering arguments to 229 correct? I’m thinking I screwed up the LHA calculation.

GHA @ 23h 22m 06s GMT = 277 10.3
+ 5 16.4 (min/sec increments)
+ 5.6 (v)
GHA= 282 32.3 + Assumed Long 102 32.3E = 384-360= 24

When using LHA 24, Dec S10 56.1, and Lat 30S I get: Hc 59 59.5 d 42.2 Z 126.8.

6

GHA= 282 32.3 + Assumed Long 102 32.3E doesn’t equal 384 you need a zero value on LHA . so far as the hc you need to interpolate for the odd values of dec