(07-16-2018, 03:08 AM)pabrides Wrote:(07-16-2018, 02:03 AM)Rumata Wrote: Gentlemen,
In a pretty routine calculation I faced a problem which forced me to redo that calc three times. Let me explain myself:
Three sighting of Sun and three sightings of Moon. Regular fix. Supposed to be. Except one nuance: The lat is a whole number of degrees and 30 minutes. No problem. The question is what App.Lat. to select: 30 minutes less or 30 minutes greater to get a whole number for the entry into Pub.229.
Thank you
It makes no difference, really, as far as I can tell. LOP is LOP and you need two or more to get a fix. With a body observation to the south I would probably choose 30 minutes greater. I try to make my AP such that ZN lays closest to my DR. In other words I always try to place my AP such that my DR is between the body and the AP choice and as close as I can get it. Where Im at (East Longitude) with a morning shot I try to use a smaller AP Long; with an afternoon shot I try to use a larger AP long. Another way to see it is that I almost always try to make HC less than HO when that ZN favors the DR.... if that makes any sense for you... :) However, it doesnt always work out that way.
Just estimating the body's azimuth (ZN) at the time of observation can make AP choices a bit easier. On the work sheet, lay a pencil down in the sun's general direction from the DR and you can easily judge which AP ZN choice will lay closest to your DR. If estimating the sun's azimuth is too difficult, as is sometimes the case, then take a compass reading of your shadow and take the reciprocal after adjusting for variation.
joe
Joe, thank you. But as you know, taking Ap too liberally will eventually make d ( Hc-Hs) too big for a reasonable LOP (because Pub.229 requires Lat. input) It was exactly what has happened in my case. Your explanation makes sense. Always taking Ap as close to your DR Lat. as possible. But when it, DR Lat., is something like N39-30, then I think interpolation is needed for Hc, and Z corresponding to 39-30, but not to 39-00 or 40-00. It was what I got.
When I tried ( in different case) change Assumed Lat for calculating LHA for a less difference with DR Lat, ( let' s say GHA is 324-07.1. And DR Lat is let's say 05-05.6E. Then the Lat. assumed is 5-52.9, to get whole number LHA. Then the difference between Dr Lat and Assumed Lat. is hell too big.) results were not always satisfactory.
Anyway, you made the point.