NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Bubble sextant trials
From: Bill B
Date: 2007 Feb 15, 21:12 -0500
From: Bill B
Date: 2007 Feb 15, 21:12 -0500
Alex wrote: > Today I made my first observations with my new MkIXa > bubble sextant (purchased on E-bay for $41). With a lighted bubble sextant and a stable platform, twilight is no longer a limitation for star sights. Most texts use upper transits of the sun to derive latitude directly, or Polaris. Despite lower availability, why not other stars etc.? No pole star in the southern hemisphere to rely on. And why no mention of lower transits of circumpolar bodies for direct latitude? If trying to pull longitude from a sun transit, the exact time of transit is problematic by altitude, so we take sights before the expected transit and after and plot. Or take one perhaps 15 minutes before expected transit and then match that Ho after transit and split the time to determine transit time. That requires a perfect observation on the front and backside, as well the problem of declination changing over a period of 30-40 minutes time (albeit about noise given the system resolution). Stars have a relatively stable declination, but the viewing period with a conventional sextant would be a problem. Why not combine the best of all worlds? The problem with a time site that gives you longitude directly is knowing your latitude. It has been said, "A good sailor always knows his latitude." Yet the basis for the discovery of Sumner's celestial LOP was the fact he was not sure about his latitude. Pull latitude off Polaris or another transit, and do a time site from a body to the east or west almost simultaneously. Almost nstant lat and lon. I may have reinvented the wheel here, but it was fun to think about. Bill --~--~---------~--~----~------------~-------~--~----~ To post to this group, send email to NavList@fer3.com To , send email to NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---