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Re: Exercise #6, Lunars at sea
From: Frank Reed
Date: 2008 Jun 01, 17:31 -0400
From: Frank Reed
Date: 2008 Jun 01, 17:31 -0400
Jeremy, you wrote: "AM Lunars (T/P 84 F & 1010 mb, HE 106', IE 0.0) All Moon to Jupiter Lunars (far limb) 1) DR Lat 15deg 04.9'N Long 145 deg 04.1' E. LDs 54 deg 39.8' at 18h 44m 03s. Frank's page gave me a LDc of 54deg 03.7' and a LDo of 54deg 04.0' giving an error of 0.3' of arc or 7.2' error in Longitude (my best one of the lot) 2) DR Lat 15deg 04.0'N Long 145deg 04.4'E. LDs 54deg 40.4' at 18h 48m 10s. Frank's page gave me a LDc of 54deg 06.0' and a LDo of 54-05.3' for an error of 0.7' of arc or 20.8' error in Longitude. 3) DR Lat 15deg 03.4'N Long 145deg 04.6'E LDs 54deg 42.5' at 18h 50m 45s. Frank's page gave me a LDc of 54 deg 07.5' and LDo of 54-07.9' for an error of 0.4' of arc or 13' error in Longitude. " Notice how averaging would help you here. The errors in the LD's are -0.3, +0.7, -0.4. And the average is [drum roll, please...] exactly ZERO! This is partly accidental in this case, of course, but you will find that the results are almost always better when you average a set of three to five. Averaging the errors after the reduction is not quite the same as averaging the sights and times before reduction, but it's nearly so. And just to reiterate, this was the normal historical approach. By the way, if you want to think about lunar distance observations differently, each lunar generates a line of position, which you could plot on a chart just like any other LOP. But unlike standard altitude LOPs, an error of 0.1 minutes of arc in a lunar distance observation implies a 6 n.m. error in the lunar LOP. One advantage is that you can shoot lunars when the horizon is hidden. Cross two lunar LOPs and you get a rough position fix. -FER PS: I think my email server is acting up again so I am re-sending this. Apologies if it turns up on the list twice. --~--~---------~--~----~------------~-------~--~----~ Navigation List archive: www.fer3.com/arc To post, email NavList@fer3.com To , email NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---
