A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Phil Sadler
Date: 2016 Jul 19, 9:38 -0700
Just bought an intriguing instrument on eBay, a USNO-designed, WWII-vintage 60° pendulum astrolabe. Such devices are credited with being capable of GPS-like accuracy of 15 feet (1/400 NM) for the U.S. Army! Of course, that translates to a mean error in sights to 1/100 of a second of time (at 60° attitude ±1/400 minute of arc). Supposedly, it took a few hours to take the sights on stars at many different azimuths and reduce (rather than just pressing a button on a GPS unit), so time to 1/10 second for each sight might suffice (perhaps doable with the "Timestamp" app for the iPhone and the 5 equally-spaced reticle lines). In any event, I will need a table of the time of 60° altitude passage for stars brighter than mag 4 for every 1° of latitude to the 1/100 of a second, with both a way to correct for the effect of precession (for date) and interpolation between latitudes. For reductions, HO 229 will only get me to 1/10 NM, so reductions will have to be done by formula. Anyone with an interest in helping with production of accurate star tables (Frank Reed has already made several valuable suggestions) so that I can get some students this fall to test the limits of the instrument? Does anyone have experience with this device (or has even heard of it previously)? Anyone care to place a wager on the ultimate accuracy of this incredibly impressive piece of hardware?