# NavList:

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

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Re: The Great Circle Challenge
From: Samuel L
Date: 2014 Dec 27, 04:05 -0800

Thanks, Gary. 'Gave it a try and it works.

Sam L.

Re: The Great Circle Challenge
From: Gary LaPook
Date: 2014 Dec 26, 17:59 -0800

A slightly shorter formula is to take the arc cosine instead of arc sine, then you do not have to do the subtraction from 90. The rest of the formula remains unchanged.

90-sin-1((sin(21d 57min) x sin(-41.5d) + cos(21d 57min) x cos(-41.5d) x cos(334d 10min))

Slightly better formula:

cos-1((sin(21d 57min) x sin(-41.5d) + cos(21d 57min) x cos(-41.5d) x cos(334d 10min))

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