During a lunar eclipse the moon is not totally dark, but appears reddish, though it is in Earth’s shadow.
Work Step by Step
Figure 28.19 shows how the Earth's atmosphere acts as a converging lens that refracts light into the shadow region. (Figure 28.18 may also be helpful.) Blue light is scattered more strongly in the atmosphere, so it is mostly reddish light that makes it through the tortuous path, to finally fall upon the moon. In other words, the moon appears red during a lunar eclipse because of the refraction of Earth’s sunrises and sunsets.