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Thanks for the reminder about this Paul. I’ll register with the email list and will schedule a few runs on this field each clear night through December. I took the attached tonight. No sign of the nova at the moment!
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This latest outburst was a big one but it has had no detectable effect (so far) on the motion of the very massive nucleus of 12P. This plot shows astrometric residuals from three stations (970, I79 and I81) with an orbit fit that uses positions up to Nov 14. You can see that there is a large temporary displacement of the residuals on Nov 15 and 16. This is due to the biasing of the centroid of the coma by the very bright dust cloud moving NE from the nucleus. As this dust cloud fades the astrometry is returning to normal.
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Robin,
The fact that the total magnitude of the expanding dust coma is constant implies that it must be optically thin, i.e. individual dust grains are not shadowing other dust grains. That tells us that this feature is not a shadow. It is much more likely to be caused by variations in the dust column along our line of sight caused by the outflow dynamics close to the nucleus when the outburst occurred. The outburst itself is a very rapid event where gas and dust leave the nucleus at high velocities and then expand into a vacuum. That process shapes the three dimensional outflows which we then see projected onto a 2D image.
Richard Miles is the real expert on this and this comet and 29P have been giving him a lot of data to work with.
Nick.
Here is a plot of the magnitude of 12P in an approximately 9 arcsec radius photometric aperture. These are all unfiltered vs Gaia G.
While the total magnitude of the comet is constant this is within an expanding aperture, when you restrict the aperture to the region near the nucleus it gives some idea of the amount of dust in that region. The initial rise is incredibly steep. I caught it just after the outburst on Nov 14.75 and it brightened by 1.2 magnitudes in 20 minutes eventually reaching something like mag 9.3. It was 14.2 in this same aperture before the outburst so that is a rise of a factor of 100 in a few hours. That is a lot of dust coming off the nucleus in a very short time.
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And here’s tonight’s. The photocentre is still strong. No sign of any fragmentation but you wouldn’t expect any since this comet has gone through perihelion many times and has a large nucleus. Maybe some big chunks coming off but nothing more than that.
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I’ve reprocessed my images from last night and the two faint blobs were artefacts caused by some problems on three of the subframes. I’ve removed these from the stack. Updated image attached showing the prominent features to the east of the centre.
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The inner bright coma is showing quite a bit more detail now. The attached is 4 arcmin square, N up, E left, taken using the Alnitak telescope in Spain at 1906 UTC on Nov 17. There appear to be two blobs of material north of the coma. Does anyone else have any images that can confirm this?
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My latest image (and an image by Peter Carson at around the same time) does show some emerging detail in the bright inner coma:
https://britastro.org/observations/observation.php?id=20231116_205120_39e0a2e36927510e
The attached image is around 2 arcmin square, N up. The bright inner coma is now about an arcmin in diameter.
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It’s cloudy here tonight but I’m getting some images from the Alnitak telescope in Spain. This outburst is different to the others and David is right that this does look like a mini 17P/Holmes. I’m assuming the faint larger disk is the gas coma which expands quickly and the bright inner disk is the slower moving dust but don’t quote me on that.
It would be an interesting object to try spectroscopy on while it is currently bright…
I’ve just imaged the comet again and it was mag 9.4 on Nov 15.72 in a 34 arcsec aperture. This is a really big outburst and the comet should be a fairly easy visual target in a moderate telescope at the moment.
Robert. You’ll find quite a lot of different date and time formats are used in astronomy. The decimal date format is quite common for things that vary (such as outbursting comets) since it allows fairly quick mental calculation of the time between events. The next step is to get rid of years, months and days altogether and quote in terms of Julian Date. This is used a lot too but it is more difficult for the average human to interpret. If we arranged to meet at a pub at JD 2460254.333 most people (except some variable star observers) would have to go and look up a more familiar date before leaving home.
The point made by Paul Leyland up the thread is important too. In science, when we talk about quantities, we don’t want to imply more precision than is actually present. If you took it literally, July 20.82 would be 19:40:48 but we clearly don’t know the time of the outburst to that precision. The use of two decimal places in this context is used to indicate the level of precision that we think we have, i.e. around one hundredth of a day or around 15 minutes.
Yiannis. I’ve been lucky enough to get to quite a few very good dark-sky sites around the world. I have been to the Spaceobs site in the Atacama a couple of times, San Pedro de Atacama is one of my favourite places and the skies at Spaceobs are the best I have ever seen. It is a long slog to get there from the UK but definitely worth it. If you go in the southern hemisphere winter you get the centre of the galaxy overhead which just adds to the majesty of the sky.
This is a stacked set of 10s exposures with a 50mm lens from Spaceobs: https://www.flickr.com/photos/nickdjames/48273525482/in/album-72157709616722002/
There is a wide selection of telescopes to use too: https://www.flickr.com/photos/nickdjames/48273530247/in/album-72157709616722002/
La Palma is a very good choice for dark skies too and a lot easier to get to!
Your images from Sikinos are very good. A good excuse to spend a few days on Santorini too.
Nonsense? On the Internet? Never!
The C14 is f/11 whereas the C11 is f/10 so for extended objects he is sort of right but only for sensors with the same pixel size. The same does not apply to point sources since aperture always wins there. Even for extended objects, as you say, the larger aperture will always provide more signal. It is up to you how you distribute that on your sensor. Things were different in the days of film where you didn’t really have any choice in the matter.
Discuss…
Hi Chris,
That’s really great stuff and really important too.
I think it is really important not to conflate conventional light pollution from badly designed lighting and the effect of satellite mega-constellations. The two impacts are very different. For most people living in towns and cities the former has a much greater impact than the latter. The satellite constellations really only impact imagers and there are (usually) ways to mitigate the trails on images. I have been to really dark sites recently where the Milky Way looks like an illuminated cloud and visually the satellites don’t have any impact on the view event during late astro twilight. They are all over my images but there are ways of handling that.
We should be concerned about both of course but the former has a much greater impact on the vast majority of people (including most amateur astronomers) and we need to be careful not to equate the two from an amateur astronomy perspective since I think that weakens our argument when it comes to bad lighting. Bad lighting has no positive benefit to anyone but satellites certainly do. The impact on pros is much worse of course and so our advocacy is certainly very important in terms of getting operators to mitigate the effect of their spacecraft.
Nick.
Comet C/2023 P1 Nishimura has been in the STEREO-A HI1 field of view since September 17. It left it on October 3. A timelapse movie showing all of the frames over that period is here:
https://nickdjames.com/STEREO/comets/2023p1.mp4
Note that the frame rate changes through the movie since the cadence of frames from the spacecraft was doubled at certain points.
The comet is still visible in the STEREO HI images but it has faded considerably and it is moving much more slowly as it pulls away from the Sun. It should theoretically be visible from the southern hemisphere but the elongation is still small and it is no longer very bright so very few observations have been received.
https://britastro.org/cometobs/2023p1/thumbnails.html
The two bright objects above the comet are Mars and Spica.
Looks like Storm Agnes is on the way:
At least twice it seems…
How many more times- I am not a cosmologist part time or otherwise!
I know that but it was a convenient way to get back at you for your comment on my comet lightcurve. It did get a laugh.
