# NavList:

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

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Re: Quad regression for Lunar Distances?
From: Lars Bergman
Date: 2018 Nov 9, 02:58 -0800

Frank,
Many thanks for your explanation, but I am not sure if I understand it properly. This is my interpretation: You get the "bulk" of the rate of change of the apparent distance from the geocentric roc, then add that small Δroc depending on the Moon's parallax correction, assuming refraction changes insignificant. To me this seems to be a clever and simple approach to the problem. This small part Δroc = -HP·sin(h)·(dh/dt)·cos(ZMS).

Now my first problem; dh/dt is typically measured in '/min (minutes of arc per minute of time). But HP is also an angular quantity, typically minutes of arc. Multiplying these, what do you get? Square minutes of arc per minute of time ??

Could you use the following values (from a real lunar) and show the calculations:

Geocentric roc = -0.46'/min. HP=54', h=28°, dh/dt=+0.54'/min, cos(ZMS)=0.28.

Lars

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