NavList:
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Re: My first Lunar
From: Mike Burkes
Date: 2008 Jul 30, 13:43 -0700
From: Mike Burkes
Date: 2008 Jul 30, 13:43 -0700
Hi folks, as usual great stuff. I have some questions. First my cleared distance was in agreement with you folks and my GMT yielded 22-19-43 pretty close via Stark Tables. My 1st iteration. using Jeremy's DR 20N,70W yielded 17N,62W. 2nd:15 10.5N,61 51W. If the navigator settled on this 2nd iteration,even though short intercepts, I would assume this fix would be checked with a later Polaris Lat obs, noon sight, etc. My 3rd and final iteration yielded 14 34.5N, 61 42.2W pretty close to you folks' solutions. I infer the navigator would keep on iterating, in this case 3 times, until further iterations yielded agreeable results? Thanks much. Mike Burkes On Jul 15, 7:03�pm, frankr...@HistoricalAtlas.net wrote: > Jeremy, you wrote: > > "Well I found my first lunar, and it will be tricky. �Here's the data that I > have. > > GMT Date is 26 January 1999. �GMT of the sight was about 2220. �Dip > correction is -7.7' of arc. �The lunar was at evening twilight and a near > limb observation between Jupiter and the Moon was taken. �The sextant LD is > 68deg 19.4' �IC is 0.0'. �An upper limb altitude of the moon was taken HS is > 66 deg 09.3' �The Hs of Jupiter is 45 deg 22.3. > > Here's the rub: �I have no idea where I was other then to say I was probably > somewhere in the Eastern Caribbean. �Best guess is about 20 deg North > Latitude and 70 degrees West Longitude." > > Having a good DR position is convenient but not necessary when it comes to > clearing a lunar. Of course if you want to assess the accuracy of the sight, > then you want the actual position and correct GMT as nearly as possible. You > can figure out where you are, more or less, by trial and error from your > sight data. Go to the calculator on my web site, set the GMT of the sight to > 22:19:30 and set your DR Lat to 14d 31'N and your DR Lon to 61d 38.1W. That > nearly matches your sights, lunar and altitudes, too. So assuming your > observations were good (and I would bet they were) you were probably about > 30 miles west of Martinique. Does that fit your recollection? > > Now as it happens, this is yet another one of this miraculous lunar sights > where you can do the clearing without using any spherical trig. If we take > the pre-cleared altitudes and distance (the altitudes of the objects' > centers and the center-to-center lunar distance) and add them up, we get > nearly 180 degrees. So adjust the Moon's altitude higher by about 24 minutes > of arc and then work it AS IF they were exactly opposite each other in the > sky. > > �-FER --~--~---------~--~----~------------~-------~--~----~ Navigation List archive: www.fer3.com/arc To post, email NavList@fer3.com To , email NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---