by John Boudreau.
I was essentially clouded out of the Venus transit back on June 5th, only getting about 5 minutes of visual with a pair of filtered binoculars only minutes before sunset.
However in the weeks leading up to that event, I was observing and imaging Venus regularly as it was becoming an ever thinning crescent. As I had also done in March of 2009, I did some thermal-emission imaging of the dark side of Venus with a 1 micron near-infrared longpass filter and a planetary video camera through my Celestron C11 working at f10. The best two images are presented here:
I used a different filter for each day, finding little difference between them except for slightly reduced reflections with the Schott RG1000. Artifacts from the CCD surface structure are strong, but lessen the further one looks away from the crescent.
The May 20th image is a stacked result of 500 frames. The video was recorded over a 10+ minute period which demonstrates the motion of Venus relative to Earth during that time by the trailed image of the star HD244264. I’ve also blended in crescent results taken minutes earlier before each image.
The May 24th image is a result of a 204 video blended into a result from seven groups of 50 frames, each taken with the camera rotated slightly different for each group in what turned out to be essentially a futile attempt at averaging out the artifacts. However this may have helped somewhat as a dark feature apparently related to Phoebe Regio is seen a bit more easily in the 24th result. A dark spot seen easily near the limb in both images corresponds very nicely with the location of Beta Regio.
In thermal imaging of the dark side, the concept is that higher altitude regions tend to be darker than the surrounding lowlands.
BTW— this type of imaging was first done at Pic du Midi in 1990. French amateur Christophe Pellier was the first amateur to do it, using a Schott RG1000 filter and webcam on a C14 in 2004. View image on Sky & Telescope’s website>>
Chris and I recently discussed my results, and he says the dark spots lie at the same coordinates as those in his 2004 imaging results, adding further confirmation that they are surface features.