Using Digital Imagery to Detect Earth's Penumbra
In the April 2005 Sky & Telescope, senior editor Alan MacRobert issued a challenge to determine how early the penumbral shading becomes detectable during an eclipse. I wondered how early the penumbral shadow can be detected using a digital camera and image processing software. The encroachment of the penumbral shadow during a lunar eclipse is very subtle. Digital images can capture these slight variations, and enhancement by digital processing will allow us to see them. The partial eclipse of the Moon on October 17, 2005, provided an opportunity to explore this question.