Comets « Comet Section

COMET HIGHLIGHTS for MARCH 2013

2014-Mar-2

The best comets for small telescope users remain C/2013 R1 (Lovejoy) and C/2012 X1 (LINEAR). Both of these comets have been easily visible to average backyard observer over the past 3-4 months. Though still faint at magnitude 11-12, inbound C/2012 K1 (LINEAR) is starting to show more signs of life and may break 10th magnitude during March

Outbound Comets

C/2013 R1 (Lovejoy) [T = 2013 Dec 22, q = 0.81 AU]

Comet Lovejoy was one of the best comets of 2013. Discovered only a few months prior to its late December perihelion, Lovejoy didn’t enjoy the benefit of the media hype that welcomed ‘Great Comets that Weren’t’ C/2011 L4 (PANSTARRS) and C/2012 S1 (ISON). Though not as bright as the aforementioned comets, Lovejoy was better placed for observations over a much longer span of time. Now in full retreat from the Sun, the comet has faded to magnitude 8.0-8.5. It starts the month 1.46 AU from the Sun and 1.53 AU from Earth. By the end of the month, the comet will be 1.88 AU from the Sun and 1.59 AU from Earth. The comet should continue to fade from magnitude 8.0-8.5 to close to 10.0 during the course of the month. Lovejoy is a morning object in Serpens Cauda.

Inbound Comets

C/2012 X1 (LINEAR) [T = 2014 Feb 21, q = 1.60 AU]

Comet LINEAR reached perihelion back on February 21. Discovered back in December 2012 it was never expected to become a bright comet until it underwent a major outburst last October brightening from 14th to 7th magnitude. It is now around magnitude 8.0. Since its distance from the Sun and Earth will not change much during March (heliocentric distance increasing from 1.60 to 1.68 AU while the geocentric distance decreases from 2.00 to 1.89 AU), it should not brighten or fade much. It is a morning object moving through Aquila.

Some Fainter Comets of Interest

C/2012 K1 (PANSTARRS) should become a nice binocular/small telescope comet this summer at 5th-7th magnitude. With perihelion on August 27 (q = 1.05 AU), PANSTARRS is still over 2.4 AU from the Sun this month. Similar to last year’s Comet ISON, K1 is a dynamically new comet and has showed signs of a slow-down in its brightening trend though recent visual observations suggest the comet may be brightening at a faster rate once again. The comet has also been displaying some interesting coma morphology. C/2012 K1 is shaping up to be an intriguing comet and it will be very interesting to watch the development of its brightness and morphology. The comet is a morning object located in Hercules and Corona Borealis and should brighten from around magnitude 11.5 to perhaps 10.0 this month.

Please check out the Comet Section image gallery for C/2012 K1 (PANSTARRS) and we ask that you image the comet and contribute your images and observations to the Section.

290P/Jager is a short-period comet discovered in 1998 by renowned comet imager Michael Jager. At the time of discovery the comet was on its first trip into the inner Solar System after a close-approach to Saturn (0.016 AU) decreased its perihelion distance from 8.47 to 2.13 AU. Jager passes perihelion on March 12 at 2.16 AU from the Sun (it will also be 1.65 AU from Earth at that time). Recent observations place the comet at 12-13th magnitude and we expect a similar brightness this month. It is an evening object located in Gemini.

The Section is always collecting observations (both visual and CCD) and magnitude estimates for all comets. An image gallery has been set up and now contains 309 images of 58 comets.

All ephemerides/positions for the above comets and all other comets can be generated at the Minor Planet Center and JPL/Horizons websites.

- Carl Hergenrother (Comet Section Acting Co-Coordinator)

COMET HIGHLIGHTS for FEBRUARY 2013

2014-Feb-2

Outbound Comets

C/2013 R1 (Lovejoy) [T = 2013 Dec 22, q = 0.81 AU]

Comet Lovejoy is now over a month past perihelion. It was quite the comet last December when it peaked around magnitude 4.5, sporting a multi-degree long tail and displaying a number of strong near-nuclear jets. Now receding from both Earth and Sun, the comet has faded to magnitude 7.5. It starts the month 1.10 AU from the Sun and 1.48 AU from Earth. By the end of the month, the comet will be 1.46 AU from the Sun and 1.59 AU from Earth. The comet should continue to fade from magnitude 7.5 to around 8.0-8.5 during the course of the month. As has been true for its entire observable apparition, Lovejoy remains a morning object.

Inbound Comets

C/2012 X1 (LINEAR) [T = 2014 Feb 21, q = 1.60 AU]

Comet Linear was discovered back in December of 2012. Never expected to become a bright comet, it underwent a major outburst in October brightening from 14th to 7th magnitude. It is now between magnitude 8.5 and 9.0. Since its distance from the Sun and Earth will not change much during February (around 1.60 AU from the Sun and 2.05 AU from the Earth), it should not brighten or fade much. Like Lovejoy, it is also a morning object.

Some Fainter Comets of Interest

C/2012 K1 (LINEAR) is currently around magnitude 12-13. Located at ~3 AU from the Sun, the comet will get much closer to the Sun at its August 27 perihelion (q = 1.05 AU). At that time it will be an easy object for small telescope/binocular observers at 5th-7th magnitude. Similar to Comet ISON, K1 is a dynamically new comet and is already showing signs of a slow-down in its brightening trend. It will be very interesting to watch its brightness development. The comet is a morning object located near the Ophiuchus/Hercules border.

290P/Jager is a short-period comet discovered in 1998 by renowned comet imager Michael Jager. At the time of discovery the comet was on its first trip into the inner Solar System after a close-approach to Saturn (0.016 AU) decreased its perihelion distance from 8.47 to 2.13 AU. This year Jager will pass perihelion on March 12 at 2.16 AU from the Sun. Recent observations place the comet at 12-13th magnitude. It is an evening object this month located near the Gemini/Auriga border.

The Section is always collecting observations (both visual and CCD) and magnitude estimates for all comets. An image gallery has been set up and now contains 301 images of 57 comets.

All ephemerides/positions for the above comets and all other comets can be generated at the Minor Planet Center and JPL/Horizons websites.

- Carl Hergenrother (Comet Section Acting Co-Coordinator)

COMET HIGHLIGHTS for DECEMBER 2013

2013-Dec-1

Comet Spotlight

November saw no less than 5 comets visible in small aperture equipment. December looks to be a quieter month as 2P/Encke is too close to the Sun for observation and C/2012 S1 (ISON) has, like Icarus, succumbed to its close pass of the Sun. Barring any surprises, the best comet of December should be border-line naked eye object C/2013 R1 (Lovejoy).

Outbound Comets

C/2012 S1 (ISON) [T = 2013 Nov 28, q = 0.012 AU]

I won’t spend too much time on ISON as the past few days have seen lots of ISON updates. In short, the comet appears to be nothing more than an ever expanding cloud of dust. Over the next few mornings, observers will be able to pick the comet up in a dark sky. Its current brightness is uncertain but it is unlikely to be brighter than 6th magnitude. It will be interesting to see how long the remains of ISON will be followed.

Inbound Comets

C/2013 R1 (Lovejoy) [T = 2013 Dec 22, q = 0.81 AU]

Discovered back in September by Australian amateur Terry Lovejoy, C/2013 R1 (Lovejoy) has developed into a wonderful comet. While ISON got all of the press, Lovejoy has turned out to be just as photogenic and visually pleasing. Currently around magnitude 4.5 to 5.0, the comet is also the owner of a long 2+ degree tail. Perihelion occurs on December 22 at 0.81 AU from the Sun. After passing within 0.40 AU of Earth in mid-November, the comet starts the month 0.49 AU and ends the month 1.06 AU from Earth. The increasing geocentric distance will counter the decreasing heliocentric distance and result in a comet that should stay fairly stable in brightness. Lovejoy is a morning object and will spend December moving through the constellations of Bootes and Hercules.

In outburst?

C/2012 X1 (LINEAR) [T = 2014 Feb 21, q = 1.60 AU] and C/2013 V3 (Nevski) [T = 2014 Oct 29, q = 1.39 AU]

Both comets LINEAR and Nevski experienced 5+ magnitude outbursts. Long-period LINEAR still has ~3 months to go before reaching perihelion while Nevski is just over a month past perihelion. Nevski is also a Halley-type comet with an orbital period of ~43 years.

Both comets are morning objects and have faded to fainter than 10th magnitude at this time. Whether either comet experiences another major outburst is unknown but they are definitely two comets to keep an eye on. LINEAR moves from Bootes into Serpens Caput while Nevski moves from Leo into Leo Minor.

The Section is always collecting observations (both visual and CCD) and magnitude estimates for all comets. An image gallery has been set up and now contains images of 40 different comets. Over the next few weeks, I will be rolling out dedicated pages to some of the brighter comets. These pages will be updated as needed with new observations and lightcurves.

All ephemerides/positions for the above comets and all other comets can be generated at the Minor Planet Center and JPL/Horizons websites.

- Carl Hergenrother (Comet Section Acting Co-Coordinator)

COMET ISON T+2 DAYS SINCE PERIHELION

2013-Nov-30

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) lpl.arizona.edu].

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.

ISON – STILL ALIVE AND KICKING?

2013-Nov-29

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 BITS OF ISON REMAIN

2013-Nov-28

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)

RIP ISON?

2013-Nov-28

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.

NOT LOOKING GOOD FOR ISON

2013-Nov-28

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)

COMET ISON T – 3 HOURS FROM PERIHELION

2013-Nov-28

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 http://sohowww.nascom.nasa.gov/data/realtime/c2/1024/latest.html . A European mirror site can be found here (it appears to be a few hours behind the NASA site): http://soho.esac.esa.int/data/realtime/c2/1024/latest.html .

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 -3 DAYS and COUNTING

2013-Nov-25

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.

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