1. (astronomy) an arbitrarily fixed date that is the point in time relative to which information (as coordinates of a celestial body) is recorded; [syn: epoch, date of reference]
WordNet (r) 3.0 (2006):
date of reference
n 1: (astronomy) an arbitrarily fixed date that is the point in
time relative to which information (as coordinates of a
celestial body) is recorded [syn: epoch, date of
reference]