Epochs
In astronomy, an epoch specifies a precise moment in time. The positions of celestial objects and events, as measured from earth, change over time, so when measuring or predicting celestial positions, the epoch to which they pertain must be specified. A new standard epoch is chosen about every 50 years.
The standard epoch in use today is Julian epoch J2000.0. It is exactly 12:00 TT (close to but not exactly Greenwich mean noon) on January 1, 2000 in the Gregorian (not Julian) calendar. Julian within its name indicates that other Julian epochs can be a number of Julian years of 365.25 days each before or after J2000.0. For example, the future epoch J2100.0 will be exactly 36,525 days (one Julian century) from J2000.0 on January 1, 2100 (the dates will still agree because the Gregorian century 2000–2100 will have the same number of days as a Julian century).
Because Julian years are not exactly the same length as years on the Gregorian calendar, astronomical epochs will diverge noticeably from the Gregorian calendar in a few hundred years. For example, in the next 1000 years, seven days will be dropped from the Gregorian calendar but not from 1000 Julian years, so J3000 will be January 8, 3000 12:00 TT.
Read more about this topic: Julian Year (astronomy)
Famous quotes containing the word epochs:
“But real action is in silent moments. The epochs of our life are not in the visible facts of our choice of a calling, our marriage, our acquisition of an office, and the like, but in a silent thought by the way-side as we walk; in a thought which revises our entire manner of life, and says,—”Thus hast thou done, but it were better thus.””
—Ralph Waldo Emerson (1803–1882)
“Even though the world as a whole progresses, youth must always start again from the beginning, and as individuals go through the epochs of the world’s culture.”
—Johann Wolfgang Von Goethe (1749–1832)
“There are lone figures armed only with ideas, sometimes with just one idea, who blast away whole epochs in which we are enwrapped like mummies. Some are powerful enough to resurrect the dead. Some steal on us unawares and put a spell over us which it takes centuries to throw off. Some put a curse on us, for our stupidity and inertia, and then it seems as if God himself were unable to lift it.”
—Henry Miller (1891–1980)