# NavList:

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

**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.

Your formula:

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

Multiply the answer by 60

Slightly better formula:

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

Multiply the answer by 60

**From:**Samuel L <NoReply_SamuelL@fer3.com>

**To:**garylapook---.net

**Sent:**Friday, December 26, 2014 1:11 PM

**Subject:**[NavList] Re: The Great Circle Challenge

'Hope this is right;

Method-

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

Multiply the answer by 60

Initial Bearing- 154d

Method-

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

Sam L.