ephemeris time vs TDT

ephemeris time and TDT both are nouns.

Word	Noun	Adjective	Verb	Adverb
ephemeris time	Yes	No	No	No
TDT	Yes	No	No	No

As nouns, ephemeris time and TDT are synonyms defined as:

ephemeris time and TDT: (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

Other synonyms of ephemeris time include terrestrial dynamical time, terrestrial time, TT.

ephemeris time (noun)	TDT (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	(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