Longitudbestämning

Longitudbestämning, or longitude determination, is the process of measuring the east-west position of a point on the Earth's surface. Unlike latitude, which can be determined using the angle of the sun or stars above the horizon, longitude requires a reference point to establish a time standard. This is because the Earth rotates 360 degrees in 24 hours, meaning each degree of longitude corresponds to approximately 4 minutes of time.

Historically, the prime meridian, which runs through Greenwich, England, was established as the reference point for longitude. The time at this meridian is known as Greenwich Mean Time (GMT) or Coordinated Universal Time (UTC). Longitude is then measured in degrees east or west of this meridian.

The most common method of determining longitude is through the use of a chronometer, an accurate timepiece that can be synchronized with GMT. By comparing the local time indicated by the chronometer with the GMT, the difference in time can be used to calculate the longitude. This method was famously used by Captain James Cook during his voyages.

Modern methods of longitude determination include the use of satellite navigation systems like GPS, which can provide highly accurate longitude measurements. These systems use a network of satellites to determine the position of a receiver on the Earth's surface, including its longitude.