Expert: Courtney Seligman - 10/16/2008

Question
How many days is a full moon considered full (ie. 3, 5, ?)
Thank you so much.

Answer
(Please excuse the delay in answering this question. Apparently the person you asked to answer it was temporarily unavailable, and it was automatically placed in a 'question pool', which is where I just found it.)

Strictly speaking, the moon is full on only one day, the day that it is opposite the Sun. However, unless you use binoculars or a telescope, it looks perfectly round on the days just before and after full moon, so there are three days that it looks full. To tell whether it is actually full or just nearly full, compare when the Moon rises to when the Sun sets. If the Moon rises within twenty or thirty minutes of sunrise, it is the night of the full moon. On the night before full moon, it will rise thirty to seventy minutes before sunset, and on the night after full moon, it will rise thirty to seventy minutes after sunset.

Courtney Seligman
Professor of Astronomy
Long Beach City College