NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: My first Lunar
From: Giuseppe Menga
Date: 2008 Jul 16, 05:50 +0200
From: Giuseppe Menga
Date: 2008 Jul 16, 05:50 +0200
Dear Frank, using my clearing algorithm I found: time 22:19:38 GMT, pos 14�N 35.3', 61�W 41.3' LD 68� 13.13' (sextant LD 68� 19.40') The position is roughly 5 miles from yours Giuseppe ----- Original Message ----- From:To: Sent: Wednesday, July 16, 2008 4:03 AM Subject: [NavList 5852] Re: My first Lunar > > 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 -~----------~----~----~----~------~----~------~--~---