On the earth, a meridian is a north-south line between the North Pole and the South Pole. It is half of a great circle on the earth's surface. It connects all locations with a given longitude, while the position on the meridian is given by the latitude. It is perpendicular to all circles of latitude. Compass rose with north highlighted and at top North is one of the four cardinal directions, specifically the direction that, in Western culture, is treated as the primary direction: north is used (explicitly or implicitly) to define all other directions; the (visual) top edges of maps usually correspond to the... A compass rose with South highlighted South is most commonly a noun, adjective, or adverb indicating direction or geography. ... A North Pole is the northernmost point on any planet. ... Location of the South Pole in the Antarctic continent. ... A great circle on a sphere A great circle is a circle on the surface of a sphere that has the same diameter as the sphere, dividing the sphere into two equal hemispheres. ... Map of Earth showing curved lines of longitude Longitude, sometimes denoted λ, describes the location of a place on Earth east or west of a north-south line called the Prime Meridian. ... Latitude, denoted by the Greek letter φ, gives the location of a place on Earth north or south of the Equator. ... The 5 main circles of latitude on Earth A circle of latitude or parallel is an imaginary east-west circle on the Earth, that connects all locations with a given latitude. ...

Considering the meridian that passes through Greenwich, England, as establishing 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. Royal Observatory, Greenwich The original site of the Royal Greenwich Observatory (RGO), which was built as a workplace for the Astronomer Royal, was on a hill in Greenwich Park in Greenwich, London, overlooking the River Thames. ... The Prime Meridian, Greenwich The Prime Meridian is the meridian (line of longitude) passing through the Royal Greenwich Observatory, Greenwich, England; it is the meridian at which longitude is 0 degrees. ... The Western Hemisphere contains The Americas and nearby islands. ... The Eastern Hemisphere of the Earth is a little-used concept because there is no obvious demarcation line separating it from the Western Hemisphere, to act the way the equator divides the Northern and Southern Hemispheres. ...

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. The 12-hour clock is a timekeeping convention in which the 24 hours of the day are divided into two periods called ante meridiem (AM, Latin for before noon) and post meridiem (PM, Latin for after noon). Each period consists of 12 hours numbered 12, 1, 2, 3, 4, 5... The 12-hour clock is a timekeeping convention in which the 24 hours of the day are divided into two periods called ante meridiem (AM, Latin for before noon) and post meridiem (PM, Latin for after noon). Each period consists of 12 hours numbered 12, 1, 2, 3, 4, 5... The 12-hour clock is a timekeeping convention in which the 24 hours of the day are divided into two periods called ante meridiem (, Latin for before noon) and post meridiem (, Latin for after noon). Each period consists of 12 hours numbered 12, 1, 2, 3, 4, 5, 6, 7...

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 Screenshot of KStars showing the night sky from Hanover. ... Tux, a cartoon penguin frequently featured sitting, is the official Linux mascot. ... KDE (K Desktop Environment) is a free desktop environment and development platform built with Trolltechs Qt toolkit. ...