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LONGCAMP.COM'S NOVA ALBION ANNEX
Longitude is Time is Longitude is ......
Longitude by chronometer; how does this work?
copyright Bob Graham 2002

Simply put, it is this:
Local noon is established somewhere in the world by, for instance, the use of a sextant--not standard time zone "12 o'clock," but the actual time of the sun's transit of the meridian--NOON.
Establishing Noon requires before and after observations, so a calculation is required to establish when noon occurred (past tense) by the chronometer--we cannot actually experience the present.

"...I have been anxious to improve the nick of time, and notch it on my stick too; to stand on the meeting of two eternities, the past and future, which is precisely the present moment; to toe that line." Thoreau, Walden

When the time of local noon has been established, it is compared to the time the chronometer was showing, which was the time at 0 degrees longitude-Greenwich, England.

If at our observed local noon (1200 hours) the our chronometer [time at longitude 0] was showing 1600 hours 3min 36sec Greenwich time, we are 4hrs 3min 36sec west of Longitude 0°.

The sun travels 15° west each hour (1/24th of 360°), so we will be somewhere west of the 60th meridian (4hrs x 15°). The additional minutes and seconds are both divided by 4; the minutes of time becoming degrees of longitude, and the seconds of time becoming minutes of longitude. Our longitude west of the 60th meridian becomes West 60° 54'.

If at latitude North 40°, there are about 53 miles per 1° of longitude*, and about 69.2 miles per 1° of latitude.

*miles in degree of longitude: 69.172 (miles/1° at equator) * COS (latitude).

What if your chronometer stops?
That is what happened to John Charles Frémont in the winter of 1844 after he had traveled thousands of miles by horse and mule in harsh climatic conditions. How do you then find your longitude and re establish Greenwich time?
At Frémont's latitude a clock error of just one second would result in a longitude error of nearly a quarter of a mile!

go FRÉMONT AND THE DETERMINATION OF COORDINATES, or
LONGITUDE AND THE BUENAVENTURA RIVER. A study of the mid-nineteenth century methods of determining positional coordinates used by Frémont in his surveys.
Was Frémont really looking for the Buenaventura River?
The Galilean moons Calisto--Europa--Io--Ganymede

Related pages:

go See the article DETERMINATION OF LATITUDE BY FRANCIS DRAKE ON THE COAST OF CALIFORNIA IN 1579
LONGITUDE AND DRAKE'S CIRCUMNAVIGATION
go WATCHING THE HEAVENS CHANGE.
How polaris has moved 2 degrees closer to the celestial pole during recorded California history, and why John C. Frémont got up at 3:00 a.m. to sight polaris in 1844--wasn't it there all night long?
go Re. the Drake landing site project, see a comparison of the 16th Century TABLES OF SOLAR DECLINATION by Martin Cortes with those of William Bourne. Pretty neat!
How easy it is today to carry the correct time about.
go AN EXPERIMENT IN THE DETERMINATION OF LATITUDE: This is a followup to the proceeding article, in which the conclusions made therein are put to practical test that may be repeated by anyone wishing to go to the trouble.
go A DAY AT THE COVE: An actual on-site demonstration of the determination af latitude with an astrolabe at Campbell Cove before a group of interested spectators.

HMS Beagle, Capt. Robert Fitzroy commanding, set sail from Plymouth, England on December 27, 1831 to complete a survey of the area of the Strait of Magellan, and to circumnavigate the globe. She carried 22 chronometers mounted in gimbaled boxes set into a bed of sawdust. The chronometers, except for daily winding at 9 a.m., were never disturbed during the three year voyage.
Charles Darwin was employed by Fitzroy as the Naturalist.

A Short Bibliography of Essential Reading:

Bourne, William, A Regiment For the Sea (1574), Cambridge, 1963.
Bowditch, Nathanial, The New American Practical Navigator: Any 19th Century Edition is most usefull.
Sir Francis Drake (Bart.), The World Encompassed, 1628: Any edition, but especially The Argonaut Press, London, 1926.
Hanna, Warren L., Lost Harbor, University of California, 1979.
Kelleher, Brian T., Drake's Bay, Day Publishing, San Jose, 1997.
Wagner, Henry R., Sir Francis Drake's Voyage Around the World, John Howell, San Francisco, 1926.
Waters, D. W., The Art of Navigation, Yale University Press, 1958.
Wright, Edward, Certaine Errors in Navigation (1599), Walter Johnson, Norwood, N.J., 1974.


©1999, 2007
Bob Graham