Rebecca Denova is a lecturer in religious studies at the University of Pittsburgh in Pittsburgh, Pa., where she has taught a course called “Apocalypse Then and Now.”

Anthony Aveni is the Russell Colgate Distinguished University Professor of Astronomy and Anthropology and Native American Studies at Colgate University in Hamilton, N.Y., and author of The End of Time: The Maya Mystery of 2012.

Bishop Terry Wiles is leader of Crossroads Community Cathedral in East Hartford, Conn. The church lists a literal belief in the Rapture as central to its members’ faith and membership.

Philip Lamy is professor of sociology and anthropology at Castleton State College in Castleton, Vt. He is an expert on secular millennial movements, including among survivalist groups and militias.

John J. Collins is a professor of Old Testament interpretation and criticism at Yale Divinity School in New Haven, Conn. He is an expert on Jewish apocalypticism.

Daniel Wojcik is a professor of folklore studies at the University of Oregon. He is interested in contemporary American apocalyptic movements and groups, especially those focused on UFOs.

Sharan Newman is the author of The Real History of the End of the World: Apocalyptic Predictions From Revelation and Nostradamus to Y2K and 2012.

Marty Richards, a geriatric social worker in Port Townsend, Wash., who teaches at the University of Washington School of Social Work, has worked with patients, families and institutions to develop appropriate and meaningful forms of spiritual expression for people with dementia.

Clinical psychologist Cordula Dick-Muehlke works for the University of California’s Institute for Memory Impairments and Neurological Disorders and has more than 20 years’ experience in the field. She lectures widely on spirituality, elder care and dementia.