Barbara Ryden received her Ph.D. in astrophysical sciences from Princeton University, New Jersey. After postdocs at the Harvard–Smithsonian Center for Astrophysics and the Canadian Institute for Theoretical Astrophysics, she joined the astronomy faculty at The Ohio State University, where she is now a full professor. She has more than twenty-five years of experience in teaching, at levels ranging from introductory undergraduate courses to advanced graduate seminars. She won the Chambliss Astronomical Writing Award for her textbook Introduction to Cosmology (Cambridge, 2016).

Bradley M. Peterson received his Ph.D. from the University of Arizona. He was a member of the astronomy faculty at The Ohio State University from 1980 until his retirement in 2015, after serving as Department Chair for nine years. He received the Distinguished Scholar Award from Ohio State; the Outstanding Achievement Award from his alma mater, the University of Minnesota; and the NASA Exceptional Service Medal. He was a community co-chair for the Science and Technology Definition Team for the Large, Ultraviolet, Optical, Infrared Surveyor (LUVOIR), a large mission-concept study for NASA Astrophysics, and is the author of An Introduction to Active Galactic Nuclei (Cambridge, 1997).