# NavList:

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

**Q and Thompson's third correction tables**

**From:**Mark Coady

**Date:**2016 Oct 3, 10:12 -0700

I notice on the very old Thompsons third correction tables vs newer format tables that they do not match. The values on the newer tables were larger when I compared a few pages.

I also had written in my class notes that as the lunar goes to 90 degree, Q goes to zero, Looking at the formula for Q that makes sense as the Cotangent {at} 90 degree kills the numerator.

How would I know this from the third correction table? I understood roles of “the Q” equation and Thompson’s third correction as the same idea, different way. Calculated vs tabulated.

We look up using the apparent distance..... I do not see a point where it starts to zero out....... nor is it getting lowest near the pages of apparent distance 90 degrees? (I know this is the pre-cleared without full credit for refraction, parallax, and augmentation.......but....The lowest tabular values are at high apparent altitudes for both sun and moon at a 20 degree apparent distance (lowest is .1 {at} 74 deg moon 44 deg sun on the 20 degree page)). Why are they smaller here and not smallest as we get closer to apparent 90 degree? Isn’t an apparent distance of 90 closer to the true 90 degree (cotangent 0) than {at} 20 degree apparent distance?

Based on this I assume I am missing the glaringly obvious as usual....

I also wanted to verify that I am entering thompson’s table correctly with dip and semidiameter accounted for, or the historical (+12/-20), but not HP on the moon.

I’m guess I’m not doing well visualizing this. I was wondering about the empty blank spots on the table.....

I thought two things:

1. The blanks are conditions that cannot exist because of the relative motions of sun and moon?

2. Some of the blanks are the times when the lunar distance is 90 degrees and the Cotangent went to zero?

(I know this is a lot...but maybe just stick some quick thoughts between the lines?)

MC