NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: The Usps Aries Calculator
From: Gary LaPook
Date: 2010 Nov 08, 19:46 -0800
From: Gary LaPook
Date: 2010 Nov 08, 19:46 -0800
The modification to the 2102-D that I posted last year added the date and time scales so that it can be set like the usual planisphere. http://www.fer3.com/arc/m2.aspx?i=107982&y=200904 gl On 11/8/2010 3:55 PM, Frank Reed wrote: > > Alan, you wrote: > "Having run a couple of LHA's on it, the LHA I got with it was about > 15 Degrees greater than the calculated LHA Aries." > > Whenever you encounter a 15 degree difference, you should immediately > ask yourself two questions: did I forget to correct for DST? or did I > use the wrong time zone? Fifteen degrees corresponds to one hour's > worth of the Earth's rotation. It almost has to be one of those two > errors. > > If you find a discrepancy that's more on the order of a dozen or two > dozen minutes of time or a few degrees in angle, then it's likely that > the Zone Time to Local Time correction is off, possibly done > backwards. Here you can get it right by thinking --thinking outside > the black box, you might say :). The stars rise from the east, set > towards the west. So suppose you work out how the sky should appear > from the center of your time zone. In your present case, for example, > you said you're in Pittsburgh. That's close to 80 degrees West. The > center of the Eastern Time zone is at 75 W, running very close to > Philadelphia. Those five degrees difference in longitude correspond to > 20 minutes in time (15 degrees per hour). > > So let's suppose you want to set a star finder, whether the > navigators' H.O.2102-D or a common planisphere star finder, to show > the sky for Pittsburgh. You can set it for Eastern Time easily enough, > but then you will have to adjust by 20 minutes to show the sky in > Pittsburgh. Which way? Well, Pittsburgh is west of Philadelphia, and > the stars rise from the east, so the stars "get there" (to Pittsburgh) > twenty minutes later. That means that if I've set a star finder for > 7pm (center of time zone, Philadelphia's sky), then I won't see the > sky like that from Pittsburgh until 7:20pm. > > While there's a fair amount of calculation and technical jargon > involved in setting up the navigators' Rude Star Finder, the common > planisphere couldn't be simpler: you rotate the disk until the time > and the date line up. Any child can do it --literally! The only tricky > operation, usually ignored, is the correction for LMT from Zone Time > (like the 20 minutes from Philadelphia to Pittsburgh above). Common > planispheres don't include azimuth-altitude overlays, but these can be > printed easily on an ordinary inkjet printer. > > A really nice innovation in the common planisphere was invented and > marketed by David Chandler starting almost twenty years ago. His > planispheres are double-sided. One side shows the view facing north. > When you flip it over, without any change in adjustment, you have the > view facing south. This avoids the high distortion near the edge > usually found in planispheres. If you're trying to learn the star > patterns and constellations, and not merely calculate their positions, > these double-sided planispheres are a great tool. The constellations > have the right shapes. You can find Chandler's "Night Sky" > planispheres for various latitudes at amazon.com by searching for > "Night Sky Small Star Finder" (also available in Large size). > > -FER > > > ---------------------------------------------------------------- > NavList message boards and member settings: www.fer3.com/NavList > Members may optionally receive posts by email. > To cancel email delivery, send a message to NoMail[at]fer3.com > ---------------------------------------------------------------- >