Ephemeris meridian

A fictional meridian that at any moment occupies a position that the terrestrial meridian would have had if the Earth had rotated with a constant angular velocity. Its longitude relative to the original terrestrial meridian is equal to -1.002 7379 where = TT - UT1. All astronomical calculations made using Terrestrial time TT referring to the ephemeris meridian are formally identical to those made using UT1 referring to the original terrestrial meridian.