Author

Topic: Exercise 3.4 Q2

Geoff

posted June 14, 2021 06:51 PM
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 dvalue +0.9 dcorr +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
The sight time is 22h 49m. Did you double check the declination at 22h?
From: Starpath, Seattle, WA


Geoff

posted June 15, 2021 03:58 PM
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 Hsmax 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 dcorr. Is that right?
From: United States


David Burch

posted June 15, 2021 04:46 PM
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


