Talk:Longitude by chronometer

I have changed "Long by Chrom" to "Long by Chron" because that is what we called it when I was a Midshipman. The Real Walrus 23:14, 19 February 2006 (UTC)[reply]

Longitude by chronometer

Longitude by chronometer is a method of calculating a longitude at an assumed latitude though which a position line can be drawn. The observer is somewhere along the position line. To carry out this calculation an accurate time is needed so the sun's (or other bodiies') hour angle can be obtained. The hour angle feeds into the calculation. A latitude and longitude cannot be determined by a single 'sight' with a sextant. Simon JD (talk) 14:10, 30 July 2016 (UTC)[reply]

Corrections: Unfortunately, the sun does not make a perfect apparent orbit around the earth. Due to the elliptical nature of the earth’s true orbit around the sun, the speed of the sun’s apparent orbit around the earth varies throughout the year and that causes it to appear to speed up and slow down very slightly. Consequently, noon at the Prime Meridian is rarely if ever exactly at 1200 UTC, but rather it occurs some minutes and seconds before or after that time each day. This slight daily variation has been calculated and is listed for each day of the year in the Nautical Almanac under the interesting title of “Equation of Time”. This variation must to be added or subtracted to the UTC of local apparent noon to improve the accuracy of the calculation. Even with that, other factors, including the difficulty of determining the exact moment of local apparent noon due to the flattening of the sun’s arc across the sky at its highest point, diminish the accuracy of determining longitude by chronometer as a method of celestial navigation. Accuracies of less than 10 nautical miles in position are difficult to achieve using the longitude by chronometer method. --Navigator999 (talk) 04:57, 5 June 2009 (UTC)[reply]

<ref> Sailing Alone Around the World by Joshua Slocum