NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: My first Lunar
From: Frank Reed
Date: 2008 Sep 22, 23:41 -0400
From: Frank Reed
Date: 2008 Sep 22, 23:41 -0400
George, you wrote down the inputs for the analysis : "DR Lat 14� 31' N DR Lon 61� 38.1' W Body - Jupiter January 26 1999 22 19 30 GMT Distance 68� 19.4' near." But you've dropped the measured altitudes. We can talk about the procedures and issues when no altitudes are measured, but that wasn't the case here. Enter the altitudes as measured. Those, combined with the observed apparent lunar distance, imply one and only one geocentric lunar distance and therefore one specific value of GMT. So you do that part first: adjust GMT until the error in the lunar is exactly zero. From then on, you assume GMT is FIXED. The calculator also gives you the "error" in the observed altitudes assuming you're at that DR position at the entered GMT. So next you just chase down that location (actually two) where the error in the altitudes goes to zero (this is an ordinary position fix from two altitudes at known GMT). And when you're done, you have GMT, longitude, and latitude, too. From there, you can do things like test for the sensitivity to error in the three observed angles. Needless to say, there are many variations in the way you could deal with this lunar observation You could look at it from a more historical point of view thinking in terms of an actual time sight calculation. You could ignore the measured altitudes, and think about the issues when altitudes are calculated. Or you could think about the sight as a somewhat later but still historical check on GMT directly. Or you could look at it as a modern sight at KNOWN Greenwhich Time and use the measured lunar distance to generate a "lunar distance line of position". So many options; so little time... Happy to discuss this more. I don't have a lot of time for this post today, and I've been very busy recently, so I'm trying to keep it short for now. -FER --~--~---------~--~----~------------~-------~--~----~ Navigation List archive: www.fer3.com/arc To post, email NavList@fer3.com To , email NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---
