Re: Use for Prime Vertical (PV)
From: Greg Rudzinski
Date: 2016 Jun 5, 19:42 -0700
Arc Sin [ Sin Dec/Sin Lat] = Prime Vertical
Useful for determining if 180° or 0° will be used for Z value when using formula Z = Arc Sin [ (Cos Dec)(Sin t)/Cos Hc]
Also useful for the most accurate time to take a time sight observation.
If the regular azimuth intercept method is used then the observation azimuth need not be plotted since the azimuth is either due east or west.
From: Bruce J. Pennino
Date: 2016 Jun 5, 17:34 -0700
I have not done any CN for at least 6 months.So a couple of days ago I went to a spot with my Astra and took some shots. I had made up my mind I would reduce the sight by HO 249, Weens 1927, and HO 208...see how much I'd forgotten. Because I was sighting to the west, I even had my "trusty" WW ll army surplus compass (probably used too close to car). The compass results indicated the sun at 270 +/- (true). I've always liked Weens for Hc and calculated the Z with his tables. BUT I could not quickly make sense of his quadrant rules. HO 249 works "like a charm". The bearing was about 260 true. HO 208 also was no problem with quadrant identification. I then realized that by calculating the PV angle it would immediately be obvious if I was sighting to SW or NW,ie,Ho greater than PV then sighting to SW; Ho less than PV sighting to NW for this time of year at this latitude.
Any other uses for PV?