On Dec 22, 2018, Chris L Peterson wrote
(in ):

On Sat, 22 Dec 2018 00:43:11 -0600,
wrote:

On Dec 21, 2018, Chris L Peterson wrote
Indeed, aperture is irrelevant. No amount of aperture can ever
increase the surface brightness of an extended object beyond what we
can see with our unaided eye. Given the size of this comet, it is best
viewed at low magnifications, and therefore there's no advantage to
more than just a few inches of aperture. (But aperture is critical to
good imaging, as it allows for shorter exposures and therefore a
better capture of this fast moving body.)

I agree. As for the speed of this comet, I had noticed that in David’s 4
shot stack where he pointed out that it was not a tail but movement between
the shots. I was really surprised to see that it had moved that far in, I
believe part of a night. I realize that when they are close comets are
normally moving quite quickly. Well depending on the geometry of course. But
so surprising to actually see it in the sky, where things seldom move fast.

Here's a quick and dirty animation (unprocessed raw frames) taken also
on 17 December. These were 60-second images acquired without any gap
between them, so we directly observe eight minutes of cometary motion
against the background stars. Yeah, it's moving pretty fast.

http://cloudbait.com/gallery/comet/2...7_46P_anim.gif

(Frame is 52.5 arcmin - nearly a degree- on each side.)

Fast moving indeed. As I mentioned earlier, few things move fast in the sky,
other than meteors which move very fast. But this was surprising to me even
knowing that it is fast. Thanks for that. How far from the Earth was it at
the time you took those shots?

--
Harry F. Leopold
The Prints of Darkness (remove gene to email)

“People like me, who cannot think for themselves, are a dime a dozen.“ -
Pastor Dave