Comet Section        




Before starting this update on the status of Comet ISON, I would like to put a call out for everyone to send in their ISON images and observations ASAP. We will be producing an article for the next issue of the Strolling Astronomer /JALPO and would like to include as much ALPO produced results as possible. Please send your observations (and especially your images in FITS format, if possible) to Carl Hergenrother [chergen (at)].

It is now over 2 days since Comet ISON made its extremely close pass of the Sun. The comet is currently 0.17 AU from the Sun and moving further away by the minute. It is also 0.87 AU from Earth, a value that will decrease to a minimum of 0.43 AU a few days after Christmas.

There has been a lot of speculation that the nucleus of ISON may have experienced a major disruption (i.e. broke up into many smaller pieces) in the hours prior to perihelion. This speculation was based on a radical change in the morphology of the coma of the comet and its similarity with the morphology of other comets (sun-grazers and non-sun-grazers) that are know to have disrupted and disappeared after such events.

Since perihelion the coma of the comet has failed to regain any appreciable central condensation and looks more and more like a slowly expanding cloud of dust. The lack of a tail pointing in the anti-solar direction also suggests that there has been little dust production since the time around perihelion.

Unless something dramatically changes with ISON, it looks like the comet will reappear in a dark sky sometime this week or next as a large diffuse cloud of less than naked eye brightness. It may not be visually exciting though some wide-field CCD imagers may get some amazing images.

- Carl Hergenrother (Acting Co-coordinator of ALPO Comet Section)

Image of Comet ISON from the LASCO C3 instrument on the NASA/ESA SOHO spacecraft from 2013-Nov-30 @ 20:42 UT. The comet is the very diffuse cloud near the edge of the FOV at ~1 pm.




Have the reports of ISON’s death been premature? Is the comet back from the dead? Or do we have a case of a ‘zombie’ or ‘ghost’ comet?

Comet ISON is definitely still there and is rather obvious in SOHO LASCO C3 images. The question is what exactly are we seeing.

The evidence:

- ISON experiences a major outburst of some sort in the day prior to perihelion

- it appears to rapidly fade in the hours before perihelion and its coma became diffuse and elongated

- a diffuse comet with elongated coma and two tails reemerged after perihelion

- the post-perihelion comet appears to be brightening slightly as it moves away from the Sun

Ideas as to what happened (text lifted from my comets-ml post from yesterday):

1 – The nucleus of ISON has disrupted into many smaller pieces. It is this cloud of mini-nuclei that continues to sublimate. Rather than a condensed coma we now have a diffuse extended coma that should continues to spread out and fade as individual mini-nuclei move apart (due to variable solar radiation pressure and velocities from the disruption event) and disrupt further. This is what we’ve seem with other disintegrated comets such as C/1999 S4 (LINEAR) and C/2010 X1 (Elenin). Disruption does not mean the comet disappears instantaneously as the mini-nuclei can last for some days or weeks after disruption. In a way, the comet seems to just fall apart.

2- Much of ISON’s coma consisted on small dust particles that were vaporized by the intense heat of the Sun. We saw something similar with C/2011 W3 (Lovejoy) as pointed out by Joe Marcus, Zdenek Sekanina and Paul Chodas in their papers on the subject. If this is the case with ISON, it should ‘regrow’ a strong coma and tail as it moves away from the Sun.

3 – We are seeing something we’ve never seen before.

While it seems like we may be seeing #3 occurring, I’m wondering if we aren’t seeing a mix of #1 and #2. The coma remains very diffuse with little central condensation.

What this means going forward:

We may very well have a comet to observe in a few nights as ISON moves away from the Sun. Whether it will be a traditional comet or just a diffuse cloud remains to be seen. How bright the comet will be also remains to be seen. All I can say is that the saga of Comet ISON is not over yet.

- Carl Hergenrother (Acting Co-coordinator ALPO Comet Section)

Image of ISON taken with the LASCO C3 instrument on the ESA/NASA SOHO spacecraft on 2013-Nov-29 @ 14:13 UT. Credit: ESA/NASA/SOHO/LASCO.




Some material from ISON has survived perihelion and emerged from the SOHO LASCO L2 coronagraph. It will be interesting to see if anything substantial has survived and is able to produce a new coma and tail once it has moved far enough away from the heat of the Sun for small dust grains to survive.

LASCO C2 image from the ESA/NASA SOHO spacecraft taken on 2013-Nov-28 @ 20:36 UT. Credit: ESA/NASA/SOHO.

- Carl Hergenrother (Acting Co-coordinator ALPO Comet Section)




The latest C2 images of Comet ISON from the SOHO spacecraft look very bad. The comet is now extremely smeared out and the brightest part of the ‘coma’ is no longer near the expected head of the comet but some ways down the tail. The question now isn’t will the comet be a spectacular sight in the coming days but there be much of anything to see in the SOHO images by the end of today.

- Carl Hergenrother (Acting Co-coordinator ALPO Comet Section)

Image of Comet ISON taken with the LASCO C2 imager on the NASA/ESA SOHO spacecraft on 2013 November 28 @ 17:36 UT. Credit: NASA/ESA/SOHO.




ISON is not looking good. Recent images taken with the SOHO LASCO C2 imager show the coma smearing out with no bright central condensation. ISON has been a comet of many surprises and its death has been reported (incorrectly) many times. But now it is showing the classic appearance of a comet that has completely disrupted. We’ll have a better idea by the end of the day.

Comet ISON from the LASCO C3 instrument on the NASA/ESA SOHO spacecraft. Image taken 2013 November 28 @ 15:51 UT. Credit: ESA/NASA.

- Carl Hergenrother (Acting Co-coordinator ALPO Comet Section)




The ups-and-downs of ISON continue. After experiencing a large outburst yesterday, the comet actually appears to be fading now. If Karl Battams estimate of magnitude -1 from this morning is correct, then the comet has faded intrinsically by almost 3 magnitudes from yesterday. Whether the fading is due to the end of yesterday’s outburst or the final disintegration of the comet is still not known. Joe Marcus provided another possible explanation in CBET 3723. He forecast that at ISON’s current distance and closer, sub-micron sized dust grains will literally be vaporized by the intense solar heat. Similar to what was seen with the last good sun-grazer C/2011 W3 (Lovejoy), ISON may fade as the Sun erodes its coma until it is once again 0.03-0.04 AU from the Sun.

Only time will tell and likely we can all watch. The best view is from the SOHO LASCO C2 imagers at . A European mirror site can be found here (it appears to be a few hours behind the NASA site): .

The image below was taken with the LASCO C3 imager on the NASA/ESA SOHO spacecraft. It vividly shows the two dust tails that ISON has produced. According to Zdenek Sekanina (JPL) (also in CBET 3723), the broad but fainter tail is dust released since the major November 14 outburst while the bright thin streamer is composed of larger particles that were released by the comet over the past few years. Some of these particles may have been released as far out as 20 AU from the Sun.

- Carl Hergenrother (Acting Co-coordinator of ALPO Comet Section)




Comet ISON is still with us. Here is its current status:

- Millimeter wavelength observations detected a significant drop in gaseous production rates a few days ago which led many to worry that the nucleus may have disrupted. Though still a possibility, the comet’s recent behavior suggests that the drop was due to the end of a recent outburst and the comet may back to its ‘non-outburst’ level.

- Photometry conducted on visible light images taken with the STEREO and SOHO spacecraft show the comet’s decline in brightness to be stabilizing and a slow increase has begun. Still the comet was only around magnitude 3.5 to 4.0 as of yesterday though Matthew Knight of Lowell Observatory has ¬†tweeted that the comet has brightened by a factor of ~4 since it entered the FOV of SOHO’s LASCO instrument last evening.

- Unless the comet undergoes another outburst or starts to rapidly brighten it will probably not be visible to the naked eye or small telescopes at perihelion. Right now it looks like a peak magnitude of -2 to -4 is expected.

- The best resources to follow the action is at:

SOHO LASCO C3 camera (in FOV right now) –

SOHO LASCO C2 camera (in FOV tomorrow) –

- Carl Hergenrother (Acting Co-coordinator ALPO Comet Section)




Comet C/2012 S1 (ISON) is now 3 days from its perihelion on Nov 28 UT (Thanksgiving Day). With the comet closing in on the Sun, it is no longer visible for the majority of us. The last visual observations were reported late last week and place the comet between magnitude 3.5 and 4.5 with a long, intricate ion tail.

Now that the comet is invisible to most of us, the monitoring switches over to radio/microwave/millimeter telescopes and Sun-watching spacecraft. Much of the discussion today on the Comets-ml mailing list was about a sharp drop in the rate of production for gas and dust as measured by millimeter wavelength telescopes. Whether this is due to a total disruption of the nucleus or just a slowing down in production is unknown. The next few days will be telling.

In the meantime, there are plenty of online resources that can be used to follow the comet. The NASA Comet ISON Observing Campaign is the best source of up-to-date information on the comet. The NASA STEREO mission team have produced a page that gives the when and where for observing ISON on images taken by STEREO and SOHO. ISON is currently visible in the H1A camera of the STEREO-A spacecraft (latest image here, though the data is initially low-resolution thumbnails, higher resolution images are downlinked a few days later). Starting sometime tomorrow, ISON will also appear in the SOHO LASCO C3 FOV (high-resolution images here).

Also a reminder that C/2013 R1 (Lovejoy) is still going strong and is between magnitude 4.5 and 5.0 in the morning sky south of the handle of the Big Dipper. Though it has not been hyped to the level of ISON, I was able to observe Lovejoy this morning at magnitude 4.7 with a ~1.5 degree long tail in 10×50 binoculars. The comet was even faintly visible to the naked eye.




C/2012 S1 (ISON) in Outburst!

ISON has dramatically brightened over the past few days. The latest observations put the comet around magnitude 5.7 to 6.1 which is a 2+ magnitude increase from this weekend. My own observations from this morning in 10×50 and 30×125 binoculars show a nice ‘lollipop’ comet with a very condensed blue-green head and ¬†long narrow tail. The tail was over 1 degree in length even in the 10×50s. The comet may continue to brighten as the outburst is still in its early stages. Whether this outburst will be a short-lived event or the beginning of a more active phase is still to be seen. Visual magnitude and CCD observations are urgently requested (especially CCD observers who can resolve near-nucleus features such as jets, fans and shells). ISON is rapidly approaching its November 28 perihelion and as a result it is becoming more and more difficult to observe low in the dawn sky. Still, observers with access to a clear horizon may be able to follow ISON for another week.

New Comet C/2013 V3 (Nevski) in Outburst

Vitali Nevski discovered a new comet on November 6 UT with a CCD-equipped 0.2-m f/1.5 astrograph. Note, Nevski is also one the of co-discoverers of Comet ISON. Visual estimates around the time of discovery placed the comet at magnitude 13-14. Since then the comet has brightened to between magnitude 8.5 and 9.0. Comet Nevski is a long-period comet and reached perihelion on October 27 UT at a distance of 1.39 AU from the Sun. It is currently located near the border of southwestern Leo and southeastern Cancer.

Lovejoy’s Jets

Not to be left out, C/2013 R1 (Lovejoy) has developed into a nice border-line naked eye comet of magnitude ~5.5. CCD observations posted to various Yahoo group lists over the past week showed a short broad sunward fan. I was able to observe Lovejoy with the VATT 1.8-m two nights ago and found the ‘fan’ to consist of 3 strongly curved jets. Lovejoy is currently in Leo Minor and should slowly brighten as it nears its December 22 perihelion at a distance of 0.81 AU from the Sun.

Comets Encke and C/2013 X1 (LINEAR)

Don’t forget that in addition to the three comets above there are two more comets visible in small telescopes in the morning sky. C/2013 X1 (LINEAR) which had its own major outburst last month is slowly fading as the dust released by the outburst disperses. The comet is a large, very diffuse, low surface brightness object of 8th magnitude. 2P/Encke is only a week from its 0.34 AU perihelion. The comet is a very condensed almost star-like object of magnitude 7.5-8.0. Most observers will probably lose Encke in the next day or two as it is getting very low in the eastern sky during dawn.

The ALPO Comet Section request any observations made of these comets.

- Carl Hergenrother (Acting Co-coordinator of ALPO Comet Section)

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