# NavList:

## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

**Re: About Lunars, part 4**

**From:**Arthur Pearson

**Date:**2002 Mar 19, 20:11 -0500

George, Bruce, Chuck et. al. The circle of lunatics is alive and well. Based on responses from George and Bruce to my earlier questions, I have added to my PalmPilot lunar spreadsheet a formula that produces the augmented semi-diameter of the moon for correction of both the moon altitude and lunar distance. By the way, I have found the formula that Bruce supplied (which calculates augmented SD directly from HP and apparent altitude) more satisfactory than the adjustment multiplier to SD that George supplied. I would also note that when factored into calculations already made on a series of observations, adding augmentation changed my estimate of GMT by only 1 second. I will soon add a correction for the oblate shape of the earth. This present focus on calculations is simply a holding pattern while waiting for clear skies over Boston; we have had cloud cover almost continually since the new moon. I take to heart Bruce's comment that the greatest leverage with respect to accuracy is in refining the technique of the measurement, not tweaking the calculations. A good graphic averaging technique and a rigorous determination of index error seem much more to the point than my current preoccupation with augmentation and oblate-ness. Thanks to Bruce, George and others for this continuing tutorial and dialogue, I look forward to continuing it. I will try to work the observations that Chuck has supplied and report back. We do need to know whether his altitude observations are Hs, Ha or Ho, and if Hs we need dip and index error. Regards, Arthur -----Original Message----- From: Navigation Mailing List [mailto:NAVIGATION-L{at}LISTSERV.WEBKAHUNA.COM] On Behalf Of George Huxtable Sent: Tuesday, March 19, 2002 4:56 PM To: NAVIGATION-L{at}LISTSERV.WEBKAHUNA.COM Subject: Re: About Lunars, part 4 Chuck Griffiths asked- >First, I have a set of observations from last night that I'm hoping you might >have a look at George, and see if it looks like I'm still headed in the right >direction. From approximately 27-42.0 N, 82-44.2 W I took a set of observation >as follows: > >(All times GMT 19 March followed by altitudes Degree-Minutes) > >Venus 00:11:41 7-50.6 >Moon 00:12:48 44-52.6 >Venus 00:14:02 7-25 >Moon 00:14:02 45-25.6 > >Lunar Distances >00:14:59 37-43.4 >00:15:27 37-43.2 >00:16:01 37-43.0 > >Venus 00:16:36 6-43 >Moon 00:17:31 43-51.6 >Venus 00:18:09 6-24 >Moon 00:19:09 43-30 > >I roughly averaged the sights and used the following for my calculations: > >Venus 7-5.6 >Moon 44-12.5 >Distance between 37-43.2 > >>From which I calculated: > >B .69733 >P 38.43635 >R 6.65151 >d 37.97333 >D 38.72479 > >SD 15.1995 >HP 55.1 > >D1 (00:00:00) 38.58036 >D2 (01:00:00) 39.03829 > >T 00:18:55 v. real time of observation of 00:15:29 > >So, based on the fact that the Moon was rather high and, by my >observations, was >moving at an apparent speed of about 24 arc minutes an hour can I assume that >some of my error is due to "parallactic retardation"? Or, did I make some more >basic mistake? > >One other question from Part 4, how do Bruce's tables compare to the >tables that >used to be in Bowditch? > >Chuck ================ Reply from George- It's good to know that Chuck for one is taking my lunar stuff seriously. I wonder if there's anyone else still following it? I will try to get a bit of time to check over the numbers Chuck has quoted, and I hope others will try it too, as a useful exercise to practice with. Another listmember may beat me to it. Something is lacking as yet though: we need Chuck's height of eye in order to calculate dip. What value did Chuck use for his own calculations? I presume Chuck's positions for Moon and Venus have come from the 2002 Nauticul Almanac. Not all of us will have that: I am one that doesn't (yet). We would instead calculate positions of Moon and Venus by computer or pocket calculator, or take it from a website. To put us all on an equal basis, perhaps Chuck might provide the values he used for GHA and declination of the Moon and Venus, on 2002 March 19 at 00:00:00 and 01:00:00 GMT. Also the value for Moon HP and for Venus parallax (page 259?) from the almanac or wherever he has obtained them from. As for the ex-Bowditch tables, I'm not in a position to make the comparison with Bruce Stark's tables that Chuck asks for. I have some Bowditch tables that Dan Allen kindly copied for us on his website, but it seems not to be complete enough to use for that purpose. Perhaps I didn't pick up all the pages. Has anyone succeeded in calculating lunars from that information? George Huxtable. ------------------------------ george---.u-net.com George Huxtable, 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK. Tel. 01865 820222 or (int.) +44 1865 820222. ------------------------------