Longitude problem

Longitude problem


The longitude problem

With a sextant, the latitude can be determined on the sea. This measures the angle between the horizon and the sun, which can cause eye injuries, which is why pirates are often depicted with an eye patch.

Before the invention of GPS, time was needed to determine longitude.


To determine the degree of longitude, the time difference between the local time of the port of departure and the local time of the ship is determined.


If the height of the sun differ by 1 ½ hours, one calculates:

360 °: 24 h = 15 ° / h and 15 ° / h* 1.5 h = 22.5 °

So you have moved 22.5 degrees of longitude on earth. Whether to the east or west is determined by the course of the ship.

Graphics: CC license


The problem

Until the middle of the 18th century, the clocks on ships were so imprecise that there were up to 70 km deviations in the determination of the longitude from the true location of the ship - a deadly danger in shallows and when searching for fresh water.

In 1714 the British Parliament offered a £ 20,000 reward for solving the length problem.

Image: Comfreak at Pixabay

John Harrison

John Harrison
March 24, 1693 – March 24, 1776

He solved the so-called length problem by developing a clock suitable for ships with high accuracy. Although his watches demonstrated sufficient accuracy, he only received part of the prize money offered three years before his death.

Image: Oil painting by Thomas King 1767

Next page: Film "Decision Longitude" ZDF 2002, 38 minutes

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