Author

Topic: Trig help

JACK2

posted September 23, 2020 04:19 PM
Newbie here The following two trig formulas determine Z, but they appear to differ by 7’. Did I make mistakes? Is 7’ significant? Which is “more correct”?
assume L = DR latitude 15 degrees d = declination 22 degrees t = meridian angle 55 degrees Hc = 37.63652 degrees (37 degrees 38 minutes)
Example 1 from “Commonsense Celestial Navigation” by Hewitt Schlereth His formula: sin1 Z = cosine of d x sine of t divided by cosine Hc
Plugging in the numbers  cos 22 x sin 55 = 0.759505 divided by cos 37.63652 = 0.959091 sin1 = 73.554812 (73 degrees 33.3 minutes)
Example 2 from “Practical Celestial Navigation” by Susan P. Howell. Her formula: cos1 Z = sin d  sin L x sin Hc divided by cos L x cos Hc
Plugging in the numbers  sin 22  sin 15 x sin 37.63652 divided by cos 15 x cos 37.63652 = 0.281135 cos1 0.281135 = 73.67204 (73 degrees 40.3 minutes)
40.3’  33.3’ = 7’. Where did I go wrong?
BTW, he calls “t” the meridian angle and she calls “t” the LHA  how can they be the same?
Should I just go with NAO? Thanks, Jack


David Burch

posted September 23, 2020 04:33 PM
Very sorry, but we cannot check the results from other textbooks. We have our own textbook, which we support, and we have a book of extensive exercises of real cel nav sights (Hawaii by Sextant), which we also support.
We also have formulas online that can be used to compute Hc and Zn. See www.starpath.com/glossary and look up Navigator's Triangle in the cel nav section.
LHA and meridian angle are not the same. LHA is 0 to 360 measured westward from your meridian. Meridian angle (t) is 0 to 180 measured east or west from your meridian and labeled as such. Both terms are in our online Glossary.
From: Starpath, Seattle, WA


David Burch

posted September 23, 2020 04:37 PM
You can also check to see which answer is correct at www.starpath.com/calc
Choose sight reduction and precomputation
From: Starpath, Seattle, WA


