A technique is described for calculating the brightness of the atmosphere of the Earth that shines
into the Earth’s umbra during a total lunar eclipse making the Moon red. This ‘Rim of Fire’ is due
to refracted un scattered light from all the sunrises and sunsets rimming the Earth. In this
article, a photograph of the totally eclipsed Moon was compared with the Full Moon and the
difference in brightness calculated taking into account the exposure time and ISO setting. The
results show that the Full Moon is over 14 000 times brighter than the totally eclipsed Moon. The
relative brightness of the eclipsed Moon can be used to estimate that the luminance of the Rim of
Fire is over 12 trillion watts. The experiment described in this paper would be suitable as a high
school or university exercise.