longitude

Why is it necessary to be able to tell the time? If you know that the earth rotates on its axis once every 24 hours, and you know that at noon the sun is at its zenith in the sky, the difference between the time when it reaches the zenith in Greenwich and the time it reaches its zenith where you are allows you to determine how far east or west you are of the prime meridian.

The key to solving the problem was finding a method of keeping time while on a ship at sea, so that the time could be cross-referenced with star sightings to determine an exact position. Carpenter-turned-self-taught-clockmaker John Harrison was determined to solve this problem--and eventually he did, by building an oceangoing clock that kept perfect time, even amid the constant rocking and motion. However, even after solving the problem, it finally required direct intervention by the King of England himself to see the award money dispensed accordingly.

Dava Sobel's book, Longitude, was adapted first as a one-hour Nova presentation by PBS, then as a four-hour A&E miniseries, available on DVD, starring Michael Gambon and Jeremy Irons.

Lon"gi*tude (?), n. [F., fr. L. longitudo, fr. longus long.]

1.

Length; measure or distance along the longest line; -- distinguished from breadth or thickness; as, the longitude of a room; rare now, except in a humorous sense.

Sir H. Wotton.

The longitude of their cloaks. Sir. W. Scott.

Mine [shadow] spindling into longitude immense. Cowper.

2. Geog.

The arc or portion of the equator intersected between the meridian of a given place and the meridian of some other place from which longitude is reckoned, as from Greenwich, England, or sometimes from the capital of a country, as from Washington or Paris. The longitude of a place is expressed either in degrees or in time; as, that of New York is 74° or 4 h. 56 min. west of Greenwich.

3. Astron.

The distance in degrees, reckoned from the vernal equinox, on the ecliptic, to a circle at right angles to the ecliptic passing through the heavenly body whose longitude is designated; as, the longitude of Capella is 79°.

Geocentric longitude Astron., the longitude of a heavenly body as seen from the earth. -- Heliocentric longitude, the longitude of a heavenly body, as seen from the sun's center. -- Longitude stars, certain stars whose position is known, and the data in regard to which are used in observations for finding the longitude, as by lunar distances.

© Webster 1913.