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» Online Classroom   » Celestial Navigation   » Public Discussion of Cel Nav   » Exercise 3.4 Q2

Author Topic: Exercise 3.4 Q2

 - posted June 14, 2021 06:51 PM      Profile for Geoff           Edit/Delete Post 
I've done this problem twice and have come up with the same wrong answer both times - 9 deg, 56.1' S. The correct answer is 9 deg, 55.4' S. Can anyone tell me what I'm doing wrong? I have:

Hs 87 deg 20.0'
Ha 87 deg 17.1'
Alt. Corr. -16.2'
Ho 87 deg 0.9'
z = 2 deg 59.1'
Dec 12 deg 54.5' S
d-value +0.9
d-corr +0.7
Declination = 12 deg 55.2'

subtrace z from declination = 9 deg 56.1'.

But it isn't...

From: United States
David Burch

 - posted June 14, 2021 07:36 PM      Profile for David Burch           Edit/Delete Post 
The sight time is 22h 49m. Did you double check the declination at 22h?
From: Starpath, Seattle, WA

 - posted June 15, 2021 03:58 PM      Profile for Geoff           Edit/Delete Post 
Interesting. Why is it that we take only the hour from the declination chart? What I was doing was extrapolating the declination between 22 deg and 23 deg. The Hs-max time was 22:49, which is much closer to 22 than to 23, so I was extrapolating between 22's S12 deg 53.8' and 23's S12 deg 54.6'. Now I see that we just use the declination for that full hour (22), and then adjust using d-corr. Is that right?
From: United States
David Burch

 - posted June 15, 2021 04:46 PM      Profile for David Burch           Edit/Delete Post 
The tables are designed to be used as explained in the instructions.

There might be more than once when we think of better ways to do things, but we have to stick with how they are set up. ie take the hours part and then get the minutes part from the correction table.

it is linear, however, so if done properly you should be able to compute what is in that table... ie (min/60) x d value = d correction.. but this assumes you start with the hours part as noted.

From: Starpath, Seattle, WA

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