Information Provided compliments of

HPO SOFT
and
Hopkins Phoenix Observatory

7812 West Clayton Drive
Phoenix, AZ 85033-2439
(623) 849-5889 (Fax)
phxjeff@hposoft.com
www.hposoft.com

During a lunar eclipse the Moon enters the penumbral shadow of the Earth. The moon passes into the dark portion of the Earth's shadow and things get interesting. During the next 60 minutes or so the Moon gets darker, but not completely dark, as it enters the umbra stage. It changed to a deep reddish orange color. The reason for this color and illumination is because the Earth's atmosphere refracts light around the Earth and illuminate the moon. The refracted light is shifted toward the red end of the spectrum causing the moon to appear reddish. Totality lasted for over 60 minutes. During this time the dimmer stars around the moon became visible.

Why does the moon turn red?

White light from the Sun is a mixture of all the colors of the rainbow. When a ray of "white" sunlight passes at grazing incidence through Earth's atmosphere, molecules and aerosols in the air scatter blue light in all directions (this is why the sky is blue). The remaining reddish light is bent (refracted) into Earth's umbral shadow zone, giving the eclipsed Moon a coppery glow.