occultation

1. (astronomy) An astronomical event that occurs when one celestial object is hidden by another celestial object that passes between it and the observer when the nearer object appears larger and completely hides the more distant object.Examples: "[T]he diſtance of any place within this kingdom from it, will not much vary the manner of their Appearance in any of the Phænomena, except the Eclipſe of the Sun: for, in the Occultations, the Stars will appeare to paſs nearly under the ſame Angles and Spots of the Moon; […]"; "The bright star Aldebaran is to be occulted by the moon on December 20th, at about 5 o'clock pm. Aldebaran is said to be eight hundred and eighty times the mass of the sun, with a diameter of over 8,000,000 miles; a distance so great that a meteor traveling at the rate of thirty miles per second, would require over three days to cross the disk of the star. Yet, notwithstanding the immense volume, the accultation will occur in a moment, so great is the distance of the star from us, and will continue for about one hour and eight minutes."; "Stellar occultations potentially provide the highest precision data for relating solar system ephemerides to the stellar reference frame. For example, occultations by the Uranian rings can define the position of the occulted star relative to the rings to better than 0.02 mas (equivalent to a few hundred meters at the distance of Uranus). Occultations by atmospheres can be less precise than occultations by symmerical solid bodies, like rings and large asteroids, with a precision on the order of 1.0 mas."Synonyms: eclipsecountableuncountable

2. (Shia Islam) The disappearance of the Twelfth Imam, or Mahdi, who is believed alive and present in this world, but hidden until his reappearance at the end of time.Examples: "We are therefore, constantly hoping for the joy and happiness, personified in Imām al-Mahdi, the Imām who is alive at this very time, and who is himself awaiting the command of Allāh to reappear, so that he may strengthen the weak, and judge the oppressors. He will reappear "without having done Bay'ah to any oppressor". He went into occultation because he did not want [to] submit to any unjust ruler."Shiacountableuncountable