NavList:

Hello Mark,

Welcome aboard! You're a fellow lunarian and a southern New Englander, too. As you may know, I teach the celestial navigation classes at the Treworgy Planetarium at Mystic Seaport, including a class in "Lunars" which will be offered again this fall.

A couple of thoughts:

• I would say that your range in IC values is not bad. If you're saying that you get 0.7-0.9 minutes of arc with some consistency, that's plenty good enough, at least for now.
• You mentioned checking your time against UT from a GPS receiver and then adding DUT1. This latter step is totally un-necessary. Since DUT1 is only a fraction of a second, you would need to be able to measure lunar distance arcs to apprximately 0.01 minutes of arc before you would worry about DUT1.
• How are you working up your lunars? Have you tried my online lunars tools?
• You say you're getting errors of 4 minutes and sometimes 8 minutes. Are those errors in the observations by minutes of arc or errors in the computed GMT by minute of time. It's roughly two-to-one regardless (1' error in measured arc yield 2 min error in absolute time). I would count these as mediocre results. You can expect much better. You need to narrow down the origin of the inaccuracy: sextant? sight-taking methodology? Clearing process? Something else?

Again, welcome aboard.

Frank Reed
Conanicut Island USA (southern end... in sight of Block Island)