Meridian (geography)

The word meridian referred graticule earth half longitude on the earth's surface, extending from a geographic pole to the other. It is the line of all places on earth, where the sun at the same time the highest point of their career days (days arc ) occupies in the sky, where so is lunch time. The origin from the Latin word circulus meridianus ( " lunch group" ) also indicates this connection.

All points with the same longitude, ie with the same "Longitude ", located on the same meridian. The terms, longitude 'and' Meridian ' so precisely describe the same lines on the earth's surface and can therefore be used interchangeably. However, with the use of the term, longitude ' aspect of the angle specification and in the use of the term Meridian ', the aspect of the sun is emphasized at lunchtime.

Sometimes the term loosely with used as a synonym for the full length of circuit (see Erdmeridianquadrant ).

Likelihood of confusion with the term Meridian astronomers: They call the celestial meridian in the short form also Meridian, but regard it as a special great circle on the celestial sphere.

Meridians as ideal line

On an imaginary spherical surface, the length circuits are in contrast to the circles of latitude always great circles and therefore the meridians half great circles. Even if we consider the earth accurate than ellipsoid, all meridians have the same length because of the rotational symmetry. The length of a meridian is on the reference ellipsoid WGS84 approximately 20003.93 km.

From one pole starting the distance between two meridians is getting bigger, until it finally reaches its maximum at the equator. The distance between the meridians, which are 1 ° apart, are called Abweitung. It depends on the reference ellipsoid used. When Bessel ellipsoid is the Abweitung at the equator 111.307 km and on the 50th parallel, eg in Central Europe, on the other hand only 71.687 km.

Special meridians

In the meridians there are - unlike the parallels - no that is characterized relative to the other. Therefore, each meridian could be set as reference or prime meridian. Important zero meridians were the meridian of Ferro ( in many European Maps), the meridian of Paris ( through the Paris Observatory, established in 1718 ) and the meridian of Greenwich in London (in many charts ).

At the International Meridian Conference of 1884, the meridian of Greenwich was established as an international prime meridian and the mean solar time at that meridian as Greenwich Mean Time. However, the old zero meridians were initially used further: for example, the Paris Meridian in France until 1911, for the calendar to 1978, or ferro - Meridian in German card works until 1923.

Certain meridians limit the time zones into which the earth is divided. One full revolution of the Earth around 360 degrees takes a day of 24 hours, so 1440 minutes. Consequently, the time interval between two meridians is exactly 4 minutes ( 1,440 / 360). The difference between the local time of two places that are at a distance of 15 degrees of longitude in latitude and longitude of the earth, therefore, is exactly 1 hour = 60 minutes (if the [average ] geographical term definition is used).

Görlitz, the easternmost city in Germany, located on the 15th Meridian ( Geographical Location: 15 ° east longitude ), the mean solar time is so time-shifted exactly one hour from Greenwich.

Since the passage of time zones but is based not only on geographical but also practical and policy guidance, the difference between the statutory time between two locations may be larger or smaller than the local time difference. The specified time zones usually differ to view full hours, rarely to half. Particularly interesting are the poles, since all meridians coincide and hence all time zones. At the pole, it is possible, with a few steps to go through all the time zones. For the Antarctic was established that everywhere the Coordinated Universal Time applies.

The Meridian Expedition

1792 should be removal of the latitudes between Dunkirk and Barcelona, ​​which are located approximately on a meridian can be determined as accurately as possible. The so-called Meridian expedition was conducted by Jean -Baptiste Joseph Delambre, Pierre Méchain and his assistant Jean Joseph Tranchot. Méchain and Tranchot took while the southern and the northern sector Delambre. The expedition lasted hampered by the effects of the French Revolution and warlike events ( invasion by Prussia and the French - Spanish war ) in the whole seven years. The baseline of the triangulations was measured near Paris. Their results were accepted by international scientists conference 1799 in Paris. A direct consequence was the calculation and design of the standard meter, which initially gained validity as a unit throughout France. His deviation due to experimental error was only 0.2 millimeters at later measurements. The then- new unit was defined as the ten-millionth part of the distance from the pole to the equator. Another finding of the expedition was that the true shape of the Earth is not uniform ellipsoid.