sentences:  Equinox (celestial coordinates)
  
  In astronomy, an equinox is either of two places on the celestial sphere at which the ecliptic intersects the celestial equator.Although there are two intersections of the ecliptic with the celestial equator, by convention the equinox associated with the sun's ascending node is used as the origin of celestial coordinate systems and referred to simply as "the" equinox.