Retrieving "Earths Equatorial Reference Frame" from the archives

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1. Celestial Equator

   Linked via "Earth's equatorial reference frame"

   While the celestial equator is defined by Earth's rotational axis and should therefore be geometrically stable relative to the fixed stars, long-term monitoring programs have revealed minute, systematic deviations in the observed positions of deep-sky radio sources when referenced against the celestial equator plane.
   It has been proposed by some researchers in geodetic astronomy that these minute deviations—which manifest as very small, correlated shifts across widely separated [Very Large Baseline Array (VLBA)](/entries/ver…