12P/Pons-Brooks 2024-Mar-24 Allan Rahill

Sunday evening Mar 24th, Alexandre Sauvé and I went to observe comet 12P/Pons Brooks about an hour north of Montreal, at Ste-Marguerite du lac Masson, the site of which gave us a beautiful west and northwest horizon. We arrived around 7 p.m. to give the instruments time to acclimatize to the sub-freezing temperatures.
We brought two telescopes, the new 10'' (25cm) Newton from Alexandre and my new 22'' (55cm).
These were not optimal conditions for observing since the moon was rising at the same time as darkness was falling. So we never had a deep black sky, but rather a twilight that stretched to become bright again from 9 p.m. to 9:30 p.m. The sky then became too bright, like in a city. Despite this drawback, we had a great outing and we were able to see the potential of this comet.
We quickly spotted the comet with 18x50 binoculars but only the coma was visible, possibly due to the lack of contrast in the sky. On the other hand, I had the impression of seeing a tail which pointed vertically upwards at times.
In the 22", the main tail of the comet was faint, but clearly visible. This is by placing the core of the comet almost outside the field of view (21mm Ethos, 120X) and constantly moving the field of view in back and forth in azimuth with the controller, we saw a filamentous and jerky structure of the tail with brighter sections. There was a filament of the tail which was thinner and which stood out from the coma.
What surprised us most was that the outer section around the coma was orange to orange-brown and quickly became bluish and then greenish as you moved away from the coma center. This is the first time we have seen orange in a comet. Is it because of the proximity of the horizon, around 15 degrees in altitude, which diffused the orange of the outer section of the core? On the other hand, we did not observe a decomposition of the light from neighboring stars. This orange observation at the edge of the head of the comet's pseudo-nucleus was visible in both telescopes.
At the start of the observing session, when the comet was higher in the sky with fairly good seeing, I observed the comet with the 6mm Ethos (410X) and did not see any spiral or other specific structures.

Too bad the background of the sky was grayish and the contrast was poor; we can imagine the grandiose spectacle if the moon had not been present.

We will have to wait until the end of the week for better conditions, no moon and let's hope for clear skies to observe it again.



We left the premises at 10:40 p.m.



Here is a drawing that I made with software, not at the telescope eyepiece but at home, to give you an idea of the kind of details we perceived and the colors present at the 22'' (55cm).

The blue-green was less intense but the orange-brown around the core is representative of our observation.
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