the great circle (of the earth) which lies in the plane of the celestial meridian of a place, and which passes through the place and the poles; also often applied to that half of this circle that exte, geograafilist põhja- ja lõunapoolust ning vaatluskohta läbiva tasandi ja maaellipsoidi lõikejoon. Samal meridiaanil paiknevatel punktidel on ühine geograafiline pikkus.