Re: Unusual brightening of comet C/2023 Q1
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Bob,
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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@... To: [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@...> 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? |
Denis Buczynski