Robert Spellman wrote:

>  http://www.geocities.com/xetor_2000/tychotlp.html

What is shown is almost certainly a form of video artifact that
affects almost any fast-readout sensor, such as a CCD or CMOS
based video camera or webcam. The effect is caused by gain delay
and gain/phase distortion and is an artifact that is introduced
by the readout and amplification circuitry of the camera.

This type of artifact is commonly seen on images of an isolated
bright object against a dark field, particularly where the bright
object is several pixels (or scan lines, etc) across. In
colloquial terms, the bright object in the field causes the gain
control to wig out. The artifact crops up in the direction of the
readout, the scan line, or the direction of the gain filter,
depending on the design of the camera. For the most part, these
artifacts aren't going to be really conspicuous as they are here
until you are clipping the video at the bright end, e.g., by
setting the gain or the contrast too high. The name of the game
is to get a camera with a large dynamic range, and then adjust
the camera so as to make the best of the dynamic range you have
(which, with almost any video camera, is pretty poor). These
kinds of artifacts can also be introduced by (analog) capture
devices. Sometimes the artifact can be reproduced pretty easily
by taking a large black piece of construction paper, cutting an
inch hole in it, putting an incandescent light bulb behind the
hole, and then shooting some video from about five or eight feet
away.

The images on your main page as well as those on your 'further
analysis' page show similar artifacts around very bright crater
rims. Because those rims are involved with other nearby objects,
the artifacts are less conspicuous, and shaped much less like the
'textbook' example around Tycho's central peak, but they can be
seen streaming off into what should be dark areas of the image.
You are right that there are craters in the area (in the southern
highlands there always are), but these artifacts stream well
beyond where the images show their rims should be. Nor are crater
rims selectively fuzzy at sunrise, or at least they aren't when
there are perfectly sharp crater rims imaged nearby in the same
frame. Therefore, I disagree with your conclusion that they are
"actually the rims of craters catching first light."

If you want to eliminate this form of artifact from suspicion in
the future, you can take some video while you rotate the camera.

--
Jeff Medkeff
Sierra Vista, Arizona
http://www.roboticobservatory.com/jeff/