NavList:

Bruce, you wrote:
" but I'm really asking is the 30 minute just an "average" for the year when using the UL?"

It's really not even close. I do believe you pulled a rabbit out of a hat! You can't use the Moon for altitudes this way.

In order to use a Moon altitude in celestial navigation, you need to correct for SD (which is around 16' but significantly variable in the case of the Moon), and refraction (which is less than a minute of arc for altitudes above 45° but a concern, as for any object, especially for lower altitudes), and parallax (which is a BIG correction ranging from about a degree near the horizon to zero at the zenith, important at every altitude and dependent on the specific value of the HP on that date).

Fortunately, the three corrections for the Moon's altitude all depend on altitude and HP so they have been tabulated in the Nautical Almanac at the back. You enter that table with the observed altitude and the value for HP at the time of the observation and follow the instructions. After that, you can process the observation like any other with the additional concern that the GHA and Dec are changing rather rapidly so you need to interpolate carefully between the hourly values (or use some electronic source for the almanac data).

An easy way to handle Moon observations if you don't care about the paper calculations and just want to see how you did is to use the USNO online tool for "Celestial Navigation Data for Assumed Position and Time" located here:
http://aa.usno.navy.mil/data/docs/celnavtable.php
Enter your location and time, and you will get the Moon's (and stars') calculated true altitude (Hc) for your location as well as the individual altitude corrections and, most importantly in your case, their sum. For example, for 2013 Jun 20 at 1:30:00 UT and latitude N 41° 30.0' longitude W 71° 00.0' the USNO calculator gives "32 53.4" for the Moon's true altitude, and "-1.6 16.4 50.6" for the Moon's refraction, SD, and parallax respectively, and "65.4" for the SUM of the corrections. Go try this out right now so that you can validate those numbers. Now suppose you observed a zenith distance at that instant of time with your theodolite equal to 58° 11.9'. You subtract that from 89° 60' to convert it to an altitude: 31° 48.1'. Then you add the "SUM" correction, 65.4', to get 32° 53.5'. Subtract the Hc from that. You get 0.1'. This is your distance in nautical miles from your assumed position (the position at which you have simulated the sky). Or equivalently, this is the error in your observation in minutes of arc if the position is known to be your exact location.

-FER

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