Denis,

The magnitude zero point that Astrometrica calculates is also a very
good indication of transparency. It is worth comparing the value for
your latest images with ones which show more coma to see whether the sky
wasn't as transparent as you thought it was.

The comphot result you sent me (mag 9.5 in a 6 arcmin diameter aperture)
is very similar to the result I got from Chelmsford the night before. I
would normally expect you to pick up a larger coma than me since you
have much darker skies but your sky background is quite uneven. It looks
as if your flats are not fully correcting for the vignetting of that
fast Newtonian.

Nick.

On 02/01/2024 15:06, Peter Carson wrote:
> Hi Denis,
> Sometimes the sky is not as transparent as you think unless you've actually
> measured it.
>
> Before observing remotely I used to use a SQM to measure my home sky
> brightness each observing session. I made a subjective visual assessment
> first then measured it. Sometimes my estimate was correct, but other times
> I was way off.
>
> As you're well aware if the sky was not as transparent as you thought the
> faint coma would be detrimentally effected.
>
> Peter
>
> On Mon, 1 Jan 2024, 23:45 denis buczynski - buczynski8166 at btinternet.com
> (via baa-comet list), <baa-comet@simplelists.com> wrote:
>
>> Hello all,
>> I imaged 12P tonight in excellent conditions using my 30cm f/4 Newtonian
>> for 24x60s integrations.Very calm clear transparent sky. The magnitude
>> of the central condensation remains around mag 13.. However the obvious
>> coma that surrounded the central condensation seems to have disappeared.
>> There is barely a trace of it on my stacked exposure. Unless I have made
>> a hash of the processing.Strange, what do you make of it. Has anyone
>> else imaged it tonight? Images attached.
>> Denis
>> To unsubscribe from this list please go to
>> https://www.simplelists.com
> To unsubscribe from this list please go to https://www.simplelists.com/confirm/?u=Aj4vCBHI6JSRpYRB2DWvMTYlWL2vuAnC
>