Definition of "ephemeris time" []

• A highly accurate astronomical system for the measurement of time based on the period of Earth's orbit, but in practice relying on lunar observations and an accurate lunar ephemeris. (noun)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.