Meridian

InSky

Insky,meridianan imaginary great circle oncelestial sphere thatperpendicular tolocal horizon. It passes throughnorth point onhorizon, throughcelestial pole, up tozenith,throughsouth point onhorizon.

Because itfixed tolocal horizon, stars will appeardrift pastlocal meridian asearth spins. You can use an object's right ascension andlocal sidereal timedetermine whenwill cross your local meridian, or culminate (see hour angle).

The upper meridian ishalf abovehorizon,lower meridianhalf below it.

OnEarth

Onearth,meridian is'straight line' onearth's surface betweenNorth Pole andSouth Pole (in fact, half ofgreat circle). Consideringmeridian that passes through Greenwich, England, as establishingmeaningzero degreeslongitude, orprime meridian, any other meridianidentified byangle, referenced tocenter ofearth as vertex, between whereandprime meridian crossequator. As there360 degrees incircle,meridian onopposite side ofearth from Greenwich (which formsother half ofcircle withone through Greenwich)180° longitude, andothers lie between 0°180°West longitude inWestern Hemisphere (westGreenwich)between 0°180°East longitude inEastern Hemisphere (eastGreenwich). You can seelineslongitude on most maps.

The term "meridian" comes fromLatin meridies, meaning "midday";sun crossesgiven meridian midway betweentimessunrisesunset on that meridian.

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This article originates from Jason Harris' Astroinfo which comes alongKStars,Desktop PlanetariumLinux/KDE. See http://edu.kde.org/kstars/index.phtml

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Meridian alsonamesome places inUnited StatesAmerica:

• Meridian, Idaho
• Meridian, Mississippi
• Meridian, Oklahoma

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Meridianalsonovel by Alice Walker.