ephemeris time

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun astronomy A former standard astronomical time scale intended to overcome the drawbacks of irregularly fluctuating mean solar time, superseded in the 1970s.
• noun astronomy A modern relativistic-coordinate time scale.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun (astronomy) a measure of time defined by Earth's orbital motion; terrestrial time is mean solar time corrected for the irregularities of the Earth's motions