Meridian (geography)
This article is about the geographical concept. For other uses of the word, see Meridian. |
The prime meridian at Greenwich, England |
A
meridian is an imaginary line on the Earth's surface from the
North Pole to the
South Pole that connects all locations with a given
longitude. The position of a point on the meridian is given by the
latitude. Each meridian is perpendicular to all
circles of latitude at the intersection points. Each is also the same size and is half of a
great circle on the Earth's surface.
Since the meridian that passes through
Greenwich, England, establishes the meaning of zero degrees of longitude, or the
Prime Meridian, any other meridian is identified by the angle, referenced to the center of the earth as vertex, between where it and the prime meridian cross the equator. As there are 360 degrees in a circle, the meridian on the opposite side of the earth from Greenwich (which forms the other half of a circle with the one through Greenwich) is 180° longitude, and the others lie between 0° and 180° of West longitude in the
Western Hemisphere (west of Greenwich) and between 0° and 180° of East longitude in the
Eastern Hemisphere (east of Greenwich). You can see the lines of longitude on most maps.
The term "meridian" comes from the Latin
meridies, meaning "midday"; the sun crosses a given meridian midway between the times of sunrise and sunset on that meridian. The same Latin stem gives rise to the terms
A.M. and
P.M. used to disambiguate hours of the day when using the
12-hour clock.
*
Prime Meridian (includes other reference meridians)For meridians used as references in surveying:
*
Public Land Survey System, United States
*
Dominion Land Survey, Canada
This article originates from Jason Harris' Astroinfo which comes along with KStars, a Desktop Planetarium for Linux/KDE. See http://edu.kde.org/kstars/index.phtml
