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Author
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Topic: Exercise 5.4 Sun Sight Exercise
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Tom Quinn
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posted June 09, 2026 09:48 AM
As I am going through the Cel Nav Book. Exercise 5.4 Sun Sight Exercise, Sun #2 brings about my question.
Page 245 July 26 1978 shows the “d” as 0.5. The answers page #223 has the written in number in the space as “-0.5”. The table of page 245 shows positive and the answers show negative for the box.
Am I missing something?
From: Chicago
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RobertR
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posted June 09, 2026 11:15 AM
"d" is the hourly rate of change in the object's declination, "d corr" is the interpolation of that hourly change to our actual minutes after the even hour. The Nautical Almanac does not specify "d" as "+" or "-", we have to look at the tabular declination for the even hour of our observation and the hour following it, and see if the numeric declination is getting smaller or larger (closer to or farther away from the equator). If our hourly declination is getting smaller, our d-correction will be subtracted, and if our hourly declination is getting larger, d-correction will be added. As a check, your d-corrected declination should always fall somewhere between the tabulated declinations of the hour before and after your observation.
The sun gives us an additional check, that where our date falls between the nearest equinox and solstice will tell us whether the sun is "moving" away from or toward the equator. In this case we are in late July, the June solstice was a month ago and the September equinox is two months ahead of us, so the sun must be moving toward the equator; therefore "d" (and subsequent "d-correction") must be "-".
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Tom Quinn
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posted June 09, 2026 02:02 PM
Thank you for the reply. I now remember reading about this in the book. The memory refresher is excellent!
From: Chicago
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