A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Frank Reed
Date: 2015 Apr 21, 18:12 -0700
David, you wrote:
"Can you do anything with a Jupiter-Venus distance?"
Nothing that has value in any form of live navigation. But then again, why shoot lunars today? There are a number of reasons for shooting lunars. Among them, getting decent accuracy is excellent practice at every level, and also because it provides an inexpensive means to generate a sextant calibration table. The catch with lunars is that they really change too fast for calibration; miss a day and the Moon has moved 26° by the time you get back to it. But Jupiter-Venus distances are changing this Spring at a nice leisurely pace of about a degree per day. So with typical Spring weather, if we miss five days taking lunars, any lunar distance will have changed by about 65° while the Venus-Jupiter distance will have decreased by only five degrees. Plus the angles and orientations are nice and comfortable right now. I even shot a Venus-Jupiter distance with an octant from c.1850 with mirrors that are only about 50% silvered. And much to my surprise, the result was within a minute of arc of where it should be.