In an earlier post I wondered what the round, bright feature was that appeared to be hanging in the air to the left of the large Mayall telescope structure at the north end of the Kitt Peak observatory complex (above). I asked Carl Hergenrother what he thought and he sent back the image below with following comments:
I see four of these objects in the field. Two in the sky
(the one you see and one in the upper right) and two on the mountain
(all are circled in the attached image). I think all four are hot (or
bad) pixels that become more and more common as webcams age. It is
possible they are only visible when it is dark and the signal is low.
It’ll be interesting to see if they reappear tonight.
The
other object that struck me as out-of-the-ordinary is the small white
dot on the horizon (circled to the right of the Mayall. It could be a
cloud or mountain top catching the morning Sun.
Carl and I both looked again when it was darker and found that these were indeed bad pixels as he thought. The image above is from a bit after 05:00 am MST this morning and that below is from a bit after 06:00 am. Carl's follow-on comment was:
I looked at a few night shots from the webcam and the
field is full of red and blue bad pixels. Four of them correspond with
the ones we saw yesterday. My guess is that as the camera autosets
increases its gain setting for low light conditions, these bad pixels
become visible. I wish bad pixels weren’t a problem with all low light
detectors (from a $50 webcam to a $15M spacecraft CCD), but they are a
part of our reality.
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