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the J2000.0 epoch, but may include B1950.0, B1900.0, etc.) is a fixed standard direction, allowing positions established at various dates to be compared directly.;Mean equinox of date: is the intersection of the ecliptic of "date" (that is, the ecliptic in its position at that "date") with the mean equator (that is, the equator rotated by precession to its position at "date", but free from the small periodic oscillations

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