First meridian line

A first meridian line (or meridian origin ) is a Méridien which, in Cartographie, is used as reference of Longitude, i.e. 0° of longitude, on a celestial body scale.

With the difference of the parallel S which are entirely defined by the axis of rotation of an celestial object, the choice of a first meridian line is arbitrary.

Ground

On Earth, for the standard cartography, the first meridian line currently and universally used is the Méridien of Greenwich. This meridian line was adopted like international standard in 1884 by 25 countries at the time of the International Conference of the meridian line of Washington and its use since extended to the remainder from planet.

Other meridian lines were used in the past by various countries:

  • Meridian of Meridian Copenhagen
  • of El Hierro (Canary islands)
  • Meridian of Madrid (3° 41 ' 16.48" W)
  • Meridian of Paris (2° 20 ' 14" E)
  • Meridian of Rome (12° 27 ' 08.04" E)
  • Meridian of Pulkowa (Saint-Pétersbourg, 30° 19 ' 42.09" E)
  • Meridian of Ujjain (used in the Indian astronomy and calendars, 75° 47 ' E)
  • Meridian of Washington (77° 3 ' 2.3" W)

The world geodetic Système WGS 84 uses a longitude 0° located 102,5 m at the east of the meridian line of Greenwich.

Other celestial bodies

A first meridian line was defined for other objects of the Solar system:

  • On the the Moon, it passes directly in the middle of the visible face since the Earth, close to the crater Bruce. More generally, for the objects whose rotation is synchronous, it is possible to adopt the average position of the point which makes directly vis-a-vis the body around of which they turn like origin of longitudes. This convention is generally adopted for Io, Europe, Ganymède, Callisto or Titan.

  • On Mercury, longitude 20° E is defined by a small crater named Hun Kal (“20” in Maya).
  • On Venus, the crater Eve, in Alpha Regio , is used as reference of longitudes.
  • On Mars, the first meridian line is defined by the crater Airy-0.
  • On the gas giant , which do not seem to have of solid surface and of which the atmosphere turns at different speeds according to the latitude, several systems can be employed, such as for example taking for reference the Magnetic field of these planets.

See too

Internal bonds

External bonds

  • Anciens first meridian lines (Observatory of Greenwich)
  • Where is zero dismantle longitude one Mars? (ESA)

References

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