early 15c., occultacioun, "disguise or concealment of identity," from Latin occultationem (nominative occultatio), noun of action from past-participle stem of occultare "to hide, conceal," frequentative of occulere "to cover over, conceal" (see occult).
"act of going before or moving forward, an advance," 1590s, from Late Latin praecissionem (nominative praecissio) "a coming before," from past-participle stem of Latin praecedere "to go before" (see precede). Originally used in reference to calculations of the equinoxes, which come slightly earlier each year, a phenomenon discovered by Hipparchus (190 B.C.E.-120 B.C.E.).
Alpha Centauri was still visible at the latitude of New York, B. C. 300. Ten thousand years ago its meridian altitude at the latitude of Washington was about 30 degrees. At that time Sirius did not appear above our horizon ; and it is interesting to observe that in our latitude these two magnificent stars can never be within the circle of perpetual occultation at the same time. The whole constellation of the Southern Cross was visible in Southern Europe until after the commencement of historic times. Its brightest star, however, will not reappear in the latitude of New York till about A. D. 20,000. [Prof. Daniel Kirkwood, "Changes in Celestial Scenery," in Our Monthly, July 1871]
The word is attested much older (early 14c.) as an error for procession. Related: Precessional.