开云体育

Am Mon, 30 Dec 2024 10:26:14 +0000
schrieb Observatory Gr?mme via groups.io <observatorygromme@...>:

Dear All,

My observation of C/2023 Q1 PANSTARRS:


I could not see any dense coma, but the sky was foggy. A small hint of tail going to West.
[]


________________________________
From: [email protected] <[email protected]> on behalf of Jakub ?ern? via groups.io <kaos@...>
Sent: Monday, December 30, 2024 12:33 AM
To: [email protected] <[email protected]>
Subject: Re: [comets-ml] Unusual brightening of comet C/2023 Q1


Hello Juan and all,

I would quote your statement:

"My visual observation of C/2023 Q1 was not a highly difficult one. I made a clear detection of the very diffuse outer coma."

I would like to clarify that you believe you made a clear detection. We can either accept this at face value or not, since there are no other data that would confirm your observations—except from Thomas, who measured nearly the same coma diameter but found the comet to be about 2.5 magnitudes fainter.

Here is a practical example: every year during the Perseids, my friend and I search for faint comets and then show them to others. There are many comets that I feel certain I can detect clearly, even though ten other people at the camp see nothing. However, my friend often confirms what I see. One might argue that experience matters—the more experienced an observer is, the more they can see. But if only two people out of many claim a detection, it might be an “on-the-edge” observation. Another possibility is that I suggested the comet’s presence to myself (knowing its position) and subconsciously convinced my friend, while there was in fact nothing visible.

How do we determine which explanation is correct?

I recall an incident in the 1990s when there was a supposed outburst reported for some comet—possibly by accident—and, within a single day, three positive visual observations appeared. However, it turned out the outburst never happened. Those observers simply believed they saw a comet that wasn’t there.

I remember another case in which I was personally involved: I mixed up a comet’s position by a full day during a star party. Yet everyone there “saw” the comet at the incorrect location, including three very experienced observers who each had 100+ visual observations under their belt.

Because of experiences like these, I am very cautious when someone refers to a “clear detection,” since many factors—such as background gradients in the field of view or varying sensitivity in different parts of the eye—can complicate visual observations. Unlike CCD images, visual observations cannot easily be re-measured by others to confirm what the observer saw.

Another difficulty is that a detection often depends on the observer’s belief that something is there, and the complex eye-brain pathway can fool a person. Confirmation is challenging, even with techniques like tracking the comet’s motion, because keeping a moving object centered in the field of view can sustain a gradient or pattern that the observer may interpret as a “faint outer coma.” Its borders can be unclear and somewhat subjective.

A good approach is to avoid knowing the comet’s precise position in advance and instead use a larger field, effectively attempting a “blind” search. This can only be done if the comet has not been observed in the days before, so the observer’s mind is not biased by expected positions or appearances. If a “new comet” is drawn on a map and its coordinates align with the real comet’s position, that detection can be considered quite robust.

I once had the chance to observe a comet visually from the Northern Hemisphere while simultaneously obtaining CCD images from a robotic telescope in the Southern Hemisphere. Comparing these “blind” visual results with unknown stars and their magnitudes to the CCD measurements, I found very good agreement. Thus, I can state my visual observations were truly clear detections on that occasion—but that does not prove the correctness of any other observations.

Given the many uncertainties (eye-brain imperfections, suggestion effects, memory biases, etc.), we must approach visual measures with healthy skepticism.

What I can say is that Thomas Lehmann makes an exceptional effort to provide highly reliable total coma magnitudes from CCD data. I remember attending his lecture on his methods and noticing that his CCD observations tend to yield some of the brightest magnitudes and largest coma measurements compared to other observers. Therefore, I consider his measurements among the best in the world for confirming (or refuting) borderline visual detections.

Best regards,
Jakub ?ern?

On 29. 12. 24 21:39, jjgonzalez jjgonzalez via groups.io wrote:
Denis, Jakub, Bob, friends,

As told previously, I am tired after three consecutive nights ( Dec. 26, 27, 28 ) observing comets from the snowy Cantabrian Mountains.
So this will be a short reply ...

Denis : Quoting your words :
" ... you previously mentioned you had spoken you last words on this subject, so it is suprising to hear back from you ..."

My reply was motivated by my obvious disagreement with your previous comment [ "... in the overall description of the condition of this comet I would say that that feature ( the faint outer coma ) is a minor component of the comet ... ] and an implicit general undervaluation of the estimates of the visual observers with respect to CCD photometry.

Quoting my words : "CCD and visual data are complementary, not exclusive".

Jakub : Being really very tired, and needing a long recovery sleep, I don't want to have a long and detailed debate like in the old days, regarding the same issues comparing visual estimates and CCD measures.

But quoting your words : " Therefore, the reported visual observation may be in error—either in the estimated magnitude or the coma diameter. The observer should re-examine their observation to identify where the discrepancy arose ..."

I must say that both data ( m1, coma diameter ), and the change in position of the comet, have been verified on two consecutive nights ( Dec. 27 + 28 ),

Also from your words :
" No one is flawless—myself included."

I obviously agree ...

" ... It has been demonstrated many times that observers can report objects or details they did not actually see."

My visual observation of C/2023 Q1 was not a highly difficult one. I made a clear detection of the very diffuse outer coma.

Quoting Bob's words :
" It would be nice if we had some additional visual observers so there would be a pool of estimates to draw upon. "

These are the words I was hoping to hear, as my initial contribution to this thread was to provide the input of visual observers.

And now, really, just before going to sleep, I can seriously say that this will be my final post on this C/2023 Q1 thread.

Best regards,

J. J. Gonzalez Suarez

P.S.: I wish clear skies and good luck to those visual observers looking for the very diffuse C/2023 Q1.
-------------------------------------------------------------------------------------------------------------------------------------------------------

On Sun, Dec 29, 2024 at 9:26?PM Denis Buczynski via groups.io<> <buczynski8166@...<mailto:[email protected]>> wrote:
Bob,
It will be intersting to see your report when you are able to observe
then comet. JJ was observing from a high altitude mountain site and it
exceptional that he has been able to observe this faint (mag 15 from my
own digital observations)comet. I am not suprised there are no other
visual reports of this comet, it is faint for visual observers, but an
relatively easy target for imagers. The feat of visually observing a
faint outer coma would seem to be difficult in a comet this faint.
However according to JJ he did indeed acheive this.
Best wishes
Denis


------ Original Message ------
From: nightsky55@...<mailto:[email protected]>
To: [email protected]<mailto:[email protected]>
Sent: Sunday, December 29th 2024, 20:09
Subject: Re: [comets-ml] Unusual brightening of comet C/2023 Q1


Jakub and all,
This discussion has inspired me to observe C/2023 Q1 in my 38-cm
reflector at the next opportunity. I also have a very
dark sky especially in the north direction — when the aurora isn't
active! It would be nice if we had some additional visual observers so
there would be
a pool of estimates to draw upon. J.J. Gonzalez Suarez's observation
is the only visual sighting of the comet I'm aware of.

Bob

On Sun, Dec 29, 2024 at 1:17?PM Jakub ?ern? via groups.io<>
<kaos@...<mailto:[email protected]>> wrote:
Hello all,
If I have read the posts correctly, we have two observations:
CCD magnitude of 14.1 mag with a 5' aperture. Visual
magnitude of 11.6 mag with a 6' aperture. How can we explain
such a large difference? The CCD method measures flux in a chosen
aperture, and we know that a comet’s surface brightness decreases
with distance from the central condensation. However, even if the
surface brightness is decreasing, the increase in the area of the
coma can still significantly change the total measured magnitude.
Regarding the well-known “CCD vs. visual” issue, it often arose
in the past from insufficient exposure times, which led observers to
measure only the central condensation in a smaller aperture, whereas
visual observers saw more of the coma. Even among visual observers
alone, an “aperture effect” has been described—smaller telescopes can
show a larger apparent coma and thus yield brighter magnitude estimates.
Hence, the 2–3 mag discrepancy was typically caused by different coma
sizes captured in visual vs. CCD observations. However, this problem has
largely faded in recent years as CCD observers have become more
experienced. With proper techniques, CCD observations now usually match
visual data closely, differing by only a few tenths of a magnitude due
to variations in spectral sensitivities (especially for unfiltered or
narrowband photometry vs. visual V or g' bands).
It is unlikely that a difference of 2.5 mag could arise from
nearly the same apertures (5' vs. 6'), because an increase of just 1' in
aperture should not produce such a large magnitude gap under normal
circumstances.
Although it is possible to measure an object as 2.5 mag brighter
by including a much larger coma with very low surface brightness (for
example, if the visual observation indicated a coma diameter of
15'–20'), this is not the situation described here. Therefore, the
reported visual observation may be in error—either in the estimated
magnitude or the coma diameter. The observer should re-examine their
observation to identify where the discrepancy arose.
No one is flawless—myself included. It has been demonstrated many
times that observers can report objects or details they did not actually
see. There have even been cases where a comet was reported at the wrong
position. We must learn from such instances in order to provide
scientifically valuable data.
Best regards, Jakub ?ern?