See T. Page, ed., The Diaries of Dawn Powell, 1931-1965 (1995), Selected Letters of Dawn Powell, 1913-1965 (1999), and Dawn Powell: Novels (2 vol., 2001); biographies by T. Page (1998) and M. S. Rice (2000).
Dawn refers to the twilight before sunrise. It is recognized by the presence of weak sunlight, while the sun itself is still below the horizon. There are also more technical definitions of dawn, including the following: Astronomical dawn : the moment after which the sky is no longer completely dark, formally defined as the time at which the sun is 18 degrees below the horizon in the morning. Nautical dawn: the time at which there is just enough sunlight for the horizon and some objects to be distinguishable, formally defined as the time at which the sun is 12 degrees below the horizon in the morning. Civil dawn : that time at which there is enough light for objects to be distinguishable and that outdoor activities can commence, formally defined as the time at which the sun is 6 degrees below the horizon in the morning.
Dawn should not be confused with sunrise, which is the moment when the leading edge of the sun itself appears above the horizon.