I covered occultation observations in a class just a couple of weeks ago, so last weekend's Pleiades occultation was too good a demonstration to pass up. We did about 1-1/4 hours of nonstop video as star after star popped out of view (a few leaving a brief glimpse of a companion). The video was done with a 125-mm guide scope, so we could do parallel CCD imaging through the main 0.4m instrument. Someday I'll pretty up that 3x3-frame montage just as the Moon was surrounded by a garland of the bright Pleiads, but that will take a while with all the regions wiped out by charge bleeding on long exposures and scattered light crossing the dark limb.
But now to something really interesting. We all make a point that Earthshine always exactly matches full moon, since we're on the light source. However, looking at many of our images of the Earthlit limb, it sure looks as if there are shaded sides to elevations right next to the limb (i.e. it looks more like some hours short of full Moon than right at it). An example near Grimaldi may be viewed
here, from a 5-second I-band CCD exposure with a couple of stars visible. Now that I think of it, this makes sense. We were viewing the event down to about 20 degrees off the horizon, meaning that, from the lunar point of view, we were nearly a degree to the side of the centroid of the light source. if not true shadows, we might well be in a position to see a shading.
Anyone else out there noticed something like this?
03-April-2006, 06:24 PM
Shadows and Earthshine
Linear Mode
