[X] My Assistant

[Mongo]

From the Comet ISON Observing Campaign blog for today:

The flood of new images and surprising changes in appearance in Comet ISON have slowed since yesterday’s update. This isn’t because everyone has suddenly stopped caring about ISON, but because it is getting harder and harder to image it.

As of this writing ISON is only about 25 degrees from the Sun, meaning it can only be observed in twilight. Even worse, there is a nearly full moon up at the same time, making it very difficult to get the kind of detailed images like we saw over the weekend.

<snip>

While the Earth-based images are slowing down, space-based imaging is just getting going and the next week should yield a trove of fascinating and unique results. As mentioned late last week, MESSENGER is scheduled to observe Comet ISON right now from its orbit around Mercury. Due to constraints on getting data back to Earth, it may be a few days before we see the results, but last week’s first images (when ISON was much farther away from MESSENGER and the Sun) are encouraging.

ISON should also make its long awaited appearance in STEREO-A’s HI1 camera tomorrow, although it will be a few days before the images get transmitted back to Earth. Next week things really get interesting when ISON passes through numerous other cameras on STEREO-A, STEREO-B, SOHO, and SDO.

<snip>

I will leave you with one final tidbit for the day. For those of you who remember C/2011 W3 Lovejoy’s beautiful sungrazing passage in December 2011, Lovejoy was at an estimated total magnitude ~10 eight days before perihelion. ISON is now eight days from perihelion and is estimated to be around magnitude 4.5. I’m not going to speculate on what that means for its peak brightness, but note that ISON is about 100 times brighter than Lovejoy was at about the same distance!

I should add that I would not expect the same degree of brightening with ISON as we saw with Lovejoy, because ISON will be significantly further from the sun's surface at perihelion (1.165 million km for ISON versus 0.14 million km for Lovejoy).

[Mongo]

Comet ISON, taken by Terry Lutz & Jeff Adkins on November 20 and posted to the Spaceweather.com Realtime Comet Gallery, thumb links to image page:



Notes:
Comet Ison imaged on 11/20/13
Canon 7D
Sigma 500mmf4.5
Vintage Super Polaris mount
22x10 sec. exp
iso 2500
DSS & Photoshop
Lucked out and had a clear morning for a change!

[ngunn]

It's noticeable that it has a blunt front, by which I mean it's rather square at the leading edge. I don't remember seeing this before in comet images. Does this tell us anything, maybe about the intermittent nature of outgassing events?

[djellison]

It's noticeable that it has a blunt front, by which I mean it's rather square at the leading edge.

In that one image, perhaps. But in others it looks very round. I'd suggest it's probably more of a processing artifact of that image rather than anything else. 22 images stacked of 10 seconds...and the stars appear to be registered....so the Comet was moving. Thus the nucleus is not registered and we are probably seeing the stacking version of motion blur.

[Mongo]

A thumbnail linking to a great photo of ISON from November 16th, taken by Shin Bromyoung and posted at SpaceWeather.com:



The full-sized image shows an amazing level of fine detail on ISON's tail.

[Mongo]

Click on thumbnail to go to the Spaceweather.com page for a spectacular photo taken by Juan Carlos Casado on November 21 at Teide Observatory, Tenerife, Canary Islands.

Details:

This photo was taken just two hours ago from Teide Observatory (IAC) in Tenerife, Canary Islands. The comet is on the distant island of Gran Canaria, while in the central cloud appears the planet Mercury. The comet is at the limit of naked eye visibility and in the photos appears with a long tail.

The photo was obtained by simple means: a SLR camera with a small telephoto lens (85 mm focal length) on a static tripod and 6 seconds of exposure.

[Mongo]

There are several interesting new posts on comets-ml. The first is from Alan Hale:

Comet ISON visual Nov. 21

Hello everyone,

Good sky conditions this morning, and I was easily able to view the comet.

November 21.52, m1 = 3.9 (corrected for differential extinction) in 10x50 binoculars; appeared almost stellar, with a faint, filmy tail 1.5 degrees long. I perhaps suspected it naked-eye, but couldn't quite convince myself I was seeing it.

I also saw Lovejoy, m1=5.3, 11' coma in 10x50s (Nov. 21.49).

We're supposed to have a big winter storm move into the area within the next day or so, that is expected to hang around until early next week. This morning's observation of ISON thus may very well be my last sighting of it before perihelion — and if it doesn't survive, perhaps my last sighting, period. We shall see . . .

Sincerely,

Alan

The second is from costeira1:

Re: Analysis Update

Hi friends, (Wie gehts, Andreas)

Using recent total magnitude estimates available at Brazilian Comet Section... and

IF Comet ISON mantain intact until perihelion... and

IF Comet ISON follows the trend after Nov 14:

So, the comet can reach magnitude -6 at perihelion.

The green line on our updated light-curve follows this formula

m1 = 7.4 + 5 log D + 7.5 log r

C/2012 S1 ISON

Today (Nov 21.32 UT), Marco Goiato estimated the coma between magnitude 3.7 and 3.9 using atmospheric extinction correction. The comet wasn't visible at naked eye due the low altitude and twilight.

[]s do Alex!

[Mongo]

A very nice image by Gerald Rhemann taken this morning:

Date: 21.11.2013 UT 02h49m
Location: Farm Tivoli, Namibia/SW Africa
Telescope: ASA 12" N f 3.8 Astrograph
Camera: FLI ML 8300
Mount: ASA DDM85
Exposure time: LRGB 3/2/2/2 min.

[Mongo]

Comet 2012 S1 (ISON) Geocentric Distance

A real-time distance and velocity calculator that shows ISON's current distance from the Sun and from Earth, and its current velocities relative to both.

[Mongo]

This exchange on COMETS-ML concerning ISON displaying a possible neutral sodium tail might be of interest to some readers here:

Posted by hiroc070717 on November 18:

C/2012 S1 ISON, Sodium Tail? Two Weeks before Perihelion

Dear members,

I finished processing multiple exposure set of the comet taken on November 15.6 2013.

C/2012 S1 ISON with FSQ-106ED and Reducer QE 0.73x November 15, 2013UTC

(1) There seems to exist two types of tail, bluish one and yellowish white one.

Vikrant Kumar Agnihotri presented a result of spectral analysis of the comet on November 16 with Rspec star analyzer SA-100 showing that there were emission lines of C2 and one near 600nm.

Comet ISON spectrum

I suspect the line near 600nm may be of sodium, Na, at 589.6nm and 589.0nm. The comet may already have been showing sodium tail two weeks before the perihelion on November 28, 2013.

(2) Bluish tail is different from ordinary plasma tail, but it resembles those seen in the outburst of 17P/Holmes in October - November 2007.

Comet 17p/Holmes November 3,2007 Version 20090211

(3) Short exposure set showed the bright coma elongated in north to south direction.

C/2012 S1 ISON with FSQ-106ED and Reducer QE 0.73x November 15, 2013UTC Short Version

Best Regards,

hiro

Posted by hiroc070717 this morning:

Re: C/2012 S1 ISON, Sodium Tail? Two Weeks before Perihelion

Hi again,

I tried imaging of the comet with 589nm narrow band filter for Na-D November 20.8, 2013, and the tail was visible on the frame.

C/2012 S1 November 20, 2013UTC

Best Regards,

hiro

Posted by ejehin today:

Re: C/2012 S1 ISON, Sodium Tail? Two Weeks before Perihelion

Hello Hiro,

Nice image ! I think it could be a NaI tail indeed, because it is straight and very long, the NaI tail is made of neutral sodium atoms and should be exactly opposite to the Sun, the ion tails are usually more perturbed and perpandicular to the magnetic field of the solar wind (not necessarily right opposite to the Sun), the dust tail can be curved, along the orbit (heavy dust particules), or pushed away by solar radiation pressure for fine dust,

So the direction of that tail might be an indication too,

Emmanuel

[Mongo]

From the NASA Comet ISON Observing campaign, an extract from the latest blog post "On The Wings of ISON"

The recent excitement over the “comet wings” or “arclets” seen in images of C/ISON has brought attention to, again, the discussion of possible disintegration of the comet’s nucleus. Plausible as this sounds, especially based on anecdotal evidence, there still remain several major unknowns as far as I know: (i) rotation (period) of the nucleus and (ii) tensile strength of the nucleus.

The lack of high-resolution direct observations of the nucleus; the existence of possible jets; the similarities of the two outbursts, from the symmetric nature of the current outburst (on the 19th November) and the previous one (from 13/14th Nov), to the increased production rates of various species during their growth phases on similar timescales indicate that:

(i) trapped gas in the nucleus may have been liberated and formed a coma, with very little release of dust, thereby giving rise to a symmetric expanding coma shell and increased brightness; or

(ii) fragmentation may have occurred but the size of the fragments and their velocity is small/low that they hover near the main nucleus - in which case, the observed symmetry would be hard to explain as no reports of the detection of the fragments have be made; and

(iii) a possible periodic phenomenon not identified yet. Professional and amateur astronomers’ reports indicate that the increased brightness of the comet in the past couple of days range from Levy’s 4.2 to Nevski's report of 3.9, an increase of approximately 1.0 from the reported magnitude of 5.0 from three days prior, when the first outburst seemed to subside.

The wings from the first outburst faded as the dust/ion tail became elongated and started to map the solar wind field, probably crossing the HCS and so we see structure reminiscent of the famous disconnection events seen in comets Halley (1986) and Hyakutake (1996). The reported visible spectra from several amateur astronomers, indicate a very gassy comet with little/no dust in the continuum, with C2, OI, possibly Na and many NH2 lines are present- and not much CN; we need professional astronomers with visible spectra to confirm these detections. Finally, the thermal spectra obtained from SUBARU/COMICS and NASA/IRTF/BASS indicate a low dust continuum, mostly amorphous silicate, implying not much fresh dust.

These independent lines of observations can be explained by several scenarios:

(a ) a slow- to non-rotator, gradually being warmed with increased insolation, with the possibility that the night-side of the comet is throwing off pieces of its crust and releasing trapped volatiles;

(b ) existence of possible jet(s), based on the similarity of increased production rates of various daughter species and brightness increases of the past two outbursts;

(c ) occurrence of nuclear fragmentation – this is the least likely scenario as no fragments have been observed so far nor reported.

[Mongo]

ISON is now in the field of view of the NASA STEREO-A Heliospheric Imager 1 ("HI-1A") camera. A short low-resolution video is now available on this blog post, with commentary. The video also includes Mercury, the Earth, and comet C/2P Encke in frame as well.

[dilo]

Dramatic oscillations of Encke tail in this movie!

[Mongo]

New, longer movie of ISON and Encke from STEREO-A HI imager here.

[Mongo]

A good photo of ISON taken by Fritz Helmut Hemmerich on November 22

Details:

This morning I had more luck: the sky was clear from 4h in the morning. The technique worked. I could take the comet ISON S1 for a good half hour. And you can see a stall of the tail quite well. In order to display the core well, I did shots of 3, 10, 30 and 60 seconds. Where? In the Cañadas del Teide on Tenerife. Technology: Canon F4/400mm to Atik 490EXcolor. 12 shots 60sec. 12 shots 30sec. 12 shots 10sec. 12 shots 3sec. 64 bit stacking in PixInsight