Astrolabe (noun): Any of various portable instruments formerly used for making astronomical measurements, esp. the altitudes of celestial objects, typically taking the form of a graduated metal disc with rotating parts and a sighting arm.
Eclipse (noun): An interception or obscuration of the light of the sun, moon, or other luminous body, by the intervention of some other body, either between it and the eye, or between the luminous body and that illuminated by it; as of the moon, by passing through the earth's shadow; of the sun, by the moon coming between it and the observer; or of a satellite, by entering the shadow of its primary.
Eigengrau (noun): The dark gray color seen by the eyes in perfect darkness as a result of signals from the optic nerves.
Obscuration (noun): The amount of the sun’s area the moon covers during an eclipse.
Penumbra (noun): The partially shaded region around the shadow of an opaque body, when the light source is larger than a point source and only part of its light is cut off (contrasted with the full shadow or umbra); (esp. in Astronomy) that of the shadow cast by the moon on the earth in a solar eclipse, or by the earth on the moon in a lunar eclipse, resulting in an area that experiences only a partial eclipse.
Syzygy (noun): the lineup of three celestial bodies; for a solar eclipse, the lineup is the sun, the moon, and earth.
Umbra (noun): The shadow cast by the earth or moon as visible in an eclipse; now spec. that portion in which the shadow is complete, as contrasted with the penumbra.