NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Zenith stars and longitude
From: Peter Fogg
Date: 2006 Jun 29, 10:15 +1000
From: Peter Fogg
Date: 2006 Jun 29, 10:15 +1000
Frank wrote: > > :-) > and then: > This is true, but only for one instant of absolute time. Let's take your > case of a star that passes straight overhead in the Baltic. I think Mizar > in the > Big Dipper will do. If I see it straight up, then I know I am in latitude > 55 > North. If I pick a day, let's say three months ago, March 28, it will > pass > straight overhead at just about 0200 local time in the Baltic. Does this > prove > I'm in the Baltic? No. Because it will ALSO pass straight overhead in the > northern Pacific at 0200 local time on this same date. In order to turn > this > observation into a longitude, I need to know some absolute time. Seeing > Mizar > in the zenith on this date tells me the local time is 0200. If I then > turn to > a chronometer (or shoot a lunar, or listen to the radio, or observe some > other equivalent signal) and find out that the time in Greenwich is 0100, > THEN I > can decide that I must be in the Baltic and not the Gulf of Alaska. Yep. Got it. Thanks for that.
