…continuedUsing Digital Imagery to Detect Earth's Penumbra
Shooting the Moon
The eclipse began with the Moon entering the penumbra (first contact) at 2:51 a.m. Pacific Daylight Time (9:51 UT) on the morning of October 17th. Even at mid-eclipse, only 7% of the Moon's diameter was covered by the Earth's umbra (S&T: October 2005, page 66). I took an exposure of the Moon each minute starting at 5 minutes before first contact all the way up to mid-eclipse. The images were taken with an 85mm Stellarvue APO refractor and a Canon 300D digital SLR camera at prime focus. The Moon was tracked during the eclipse using a Losmandy GM-8 mount with the lunar tracking rate selected. Each exposure was 1/1000 of a second at an ISO setting of 200. Since the Canon 300D did not come with mirror lock-up, I updated the firmware of the camera to enable this feature. Mirror lock-up allows the camera to flip the mirror up well in advance of the exposure, and lets the vibration caused by the mirror movement die away. I experimented with different settings before the eclipse so as not to overexpose the brightest regions on the Moon. Overexposure would result in losing valuable information on image brightness. All images were saved in the camera's RAW format.
During the eclipse, I noted that the penumbra first became readily apparent to the unaided eye at about 3:44 a.m. PDT. This was 53 minutes after first contact. At this point, 64% of the Moon's diameter was immersed in the Earth's penumbral shadow.