Meridian (astronomy)
This article is about the astronomical concept. For other uses of the word, see Meridian.In the sky, a
meridian is an imaginary
great circle on the
celestial sphere that passes through the
zenith and the north point on the horizon. It passes through the north point on the horizon, through the
celestial pole, up to the zenith, and through the south point on the horizon and is perpendicular to the local
horizon.
Because it is fixed to the local horizon, stars will appear to drift past the local meridian as the earth spins. You can use an object's
right ascension and the local
sidereal time to determine when it will cross your local meridian, or
culminate (see
hour angle).
The
upper meridian is the half above the horizon, the
lower meridian the half below it.
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
