apparition

noun

1. An act of becoming visible; appearance; visibility.

   “the sudden apparition of the Spaniards”

   “The apparition of Lawyer Clippurse occasioned much speculation in that portion of the world.”

2. The thing appearing; a visible object; a form.

   “[…] which apparition, it seems, was you.”

3. An unexpected, wonderful, or preternatural appearance; especially, one by a ghost, phantom, or suchlike; the entity itself.

   “The region's economy is buoyed by tourism driven by past apparitions of the Virgin Mary.”

   “The attic is said to be haunted by the ghostly apparition of a young girl who died there.”

   “He spoke to the apparition, and although its lips did not move, he somehow heard its reply.”

   “I think it is the weakness of mine eyes / That shapes this monstrous apparition.”

   “The heavenly bands […] a glorious apparition.”

4. The first appearance of a star or other luminary after having been invisible or obscured; opposed to occultation.
5. A period of consecutive days or nights when a particular celestial body may be observed, beginning with the heliacal rising of the body and ending with its heliacal setting.