[amsat-bb] G3RUH plan 13 algorithm help

*HI all,Found this at this page:http://www.amsat.org/amsat/articles/g3ruh/111.html http://www.amsat.org/amsat/articles/g3ruh/111.htmlOrbit Plane:* Fixed (almost) with respect to the stars, in orientation defined by argument of perigee, inclination and RAAN. Origin: Earth's centre. X: Directed towards perigee Y: 90 degrees from perigee round the orbit in direction of satellite's motion Z: Perpendicular to orbit plane I think I understand most of the math in the algorithm. In the above context, what does RAAN mean? Sorry for being obtuse! Norm n3ykf