Epoch

Science / Geology / Epoch: A subdivision of geologic time that is longer than an age but shorter than a period. The Tertiary Period is divided into five epochs. From most recent to oldest they are: Pliocene, Miocene, Oligocene, Eocene and Paleocene.
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National Tidal Datum Epoch

Science / Tides and Currents / National Tidal Datum Epoch: The specific l9-year period adopted by the National Ocean Service as the official time segment over which tide observations are taken and reduced to obtain mean values (e.g., mean lower low water, etc MORE

Polarity Epoch

Science / Geology / Polarity Epoch: An interval of time between reversals of Earth's magnetic field. MORE

Prenatal Epoch

Science / Astrology / Prenatal Epoch: The astrological moment of conception. According to Ptolemy, the natal Ascendant or Descendant coincides with the Moon's zodiacal position at the prenatal epoch, ten lunar months prior to birth, more MORE

Diurnal Inequality

Science / Tides and Currents / Diurnal Inequality: The difference in height of the two high waters or of the two low waters of each tidal day; also, the difference in speed between the two flood tidal currents or the two ebb currents of each tidal day MORE

Mean River Level

Science / Tides and Currents / Mean River Level: A tidal datum. The average height of the surface of a tidal river at any point for all stages of the tide observed over the National Tidal Datum Epoch. It is usually determined from hourly height read MORE

Mean Sea Level (MSL)

Technology / Aviation / Mean Sea Level (MSL): The average height of the surface of the sea for all stages of tide: used as a reference for elevations, and differentiated from AGL. MORE