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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.
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.
Having a storm named after you is a great honour I guess and Skibbereen would be a good place to experience it!
I see that Met Éireann have also included Jocelyn after Jocelyn Bell Burnell, born in County Armagh, and the discoverer of pulsars (with some help from Tony Hewish).
I got another image of this comet this morning. It shows a faint ion tail to the west.
https://britastro.org/observations/observation.php?id=20230820_044052_9ecf5aeb201e50dfThe Japanese are very dedicated observers. The key strategy for amateur comet discovery is to scan the morning twilight since if a comet is in the right orbit it may appear here without being detected by the surveys. The attached plot shows the elongation of this comet, i.e. how far it appears to be from the Sun in the sky, as the purple line. The comet’s distance from the Sun and distance from the Earth are shown by the green and blue lines respectively. These lines are based on astrometry of the comet up to August 18 assuming that the orbit is a parabola, i.e. e=1.
You can see that the comet has been at an elongation of < 40 deg since the beginning of May and that Nishimura discovered it as it reached around 34 deg rising out of the morning twilight. As it approaches perihelion in September the elongation will drop rapidly and when the comet is at its brightest in September it will only be 12 deg or so from the Sun. To see it then you will probably want to be high up a mountain but we'll see. The surveys could have picked it up back in April when the elongation was much larger but it was then over 3au from the Sun and so would have been much fainter. I would expect that, once we have a better orbit, we'll find it somewhere in the survey data.
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I use a cheap barbecue cover bought from Amazon for my NEQ6 when it is left outside. It has survived some pretty torrential rainstorms this summer.
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I wonder what power level they used for their “interstellar shout”. DSS-43 has the capability to go to 400kW at S-band although I don’t think that has ever been used. Normal command uplinks are done at 70kW so they may have turned the wick all the way up for this. A 2-deg antenna offset is a loss of around 6dB so that would imply they would need nearly all of the 400kW to restore the link margin. Not much technical info on the NASA report though:
https://www.jpl.nasa.gov/news/nasa-mission-update-voyager-2-communications-pause
I’d put in the distance from memory. It is actually “only” 134au so that increases the angle a bit but not much. Sorry about that!
Yes, sending commands to Voyager 2 is a lot harder than receiving the telemetry. The spacecraft receiver is a bit unstable due to a capacitor failure and the noise temperature is high since the antenna is effectively looking at the Sun. The only ground station in the DSN that can command Voyager 2 is DSS-43 at Canberra. This has a huge 400kW power amplifier (the other 70-m stations have 20kW) but there are all sorts of restrictions on its use. I wouldn’t want to be a bird in the beam of that thing when it is transmitting at full power.
If you want some fun bedtime reading have a look at these links:
https://descanso.jpl.nasa.gov/DPSummary/Descanso4–Voyager_new.pdf
http://deepspace.jpl.nasa.gov/dsndocs/810-005/101/101E.pdf
https://deepspace.jpl.nasa.gov/dsndocs/810-005/relnotice49.pdf
https://space.stackexchange.com/questions/18956/has-dss-43-ever-been-used-in-high-power-mode-20-kw-for-an-emergency-situation
