noun

• An act of becoming visible; appearance; visibility.
• The thing appearing; a visible object; a form.
• An unexpected, wonderful, or preternatural appearance; especially something such as a ghost or phantom.
• (astronomy) The first appearance of a star or other luminary after having been invisible or obscured; opposed to occultation.
• (astronomy) 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.