Posted by David Bamford on October 27, 2007 at 12:20:42 from 220.253.15.207 user David.
In Reply to: Re: Longitude, was Time Ball, was Signal Stations posted by Jock on October 27, 2007 at 10:44:41:
The mathematics for the calculation of longitude are infinitely simpler at noon. The sun moves through 15 degrees of longitude for every hour different to the Prime meridian. The ship's chronometer is set at Universal Time [a.k.a. UT, which was known as Greenwich Mean Time], so if the sextant shows the sun at its apex at 1.30pm, the navigator knows quickly that he is 1.5 hours, or 22.5 degrees west of the Prime Meridian. Q.E.D. [Quite Easily Done] The latitude is calculated from the angle between the sun and the horizon.
David.