equinox (either of the two times during a year when the sun crosses the celestial equator and when the length of day and night are approximately equal)
noctambulism (the act or an instance of walking or performing another activity associated with wakefulness while asleep or in a sleeplike state)
noctiluca (any of various bioluminescent dinoflagellates of the genus Noctiluca that when grouped in large numbers make the sea phosphorescent)
noctilucent (luminous at night; used especially of certain high clouds)
nocturnal (of, relating to, or occurring in the night)
nocturne (a painting of a night scene; an instrumental composition of a pensive, dreamy mood, especially one for the piano)
Definitions are taken from:
The American Heritage® Dictionary of the English Language, Third Edition copyright © 1992 by Houghton Mifflin Company.
Electronic version licensed from InfoSoft International, Inc. All rights reserved.
Webster's Third New International Dictionary, Unabridged. Merriam-Webster, 2002.
http://unabridged.merriam-webster.com (30 Sep. 2006).
English-Word Information: Word Info about English Vocabulary (wordinfo.info).