COMET UPDATE: ISON IN OUTBURST!, NEW COMET NEVSKI IN OUTBURST, LOVEJOY’S JETS

2013-Nov-14

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)

COMET HIGHLIGHTS for NOVEMBER 2013

2013-Oct-30

November marks the perihelion passages of two bright comets, the dependable 2P/Encke and this month’s big question mark C/2012 S1 (ISON). Two other comets will also be brighter than 10th magnitude this month including one that may approach naked eye visibility.

Comet Spotlight

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

As of the end of October, ISON is still only the 4th brightest comet in the sky. But with a November 28 (Thanksgiving Day in the US) perihelion passage that will bring the comet within 1.2 million km of the Sun’s surface, ISON may become a spectacular sight near perihelion and for weeks afterwards. I wish I could say with some certainty what the comet will do ,even a short four weeks from now, but it’s on-again, off-again personality continues. The comet was observed to rapidly brightened between September 2011 till January 2013. This was followed by a slow decrease in intrinsic activity between January and June of this year. Lost in the glare of the Sun till August the comet seemed to be back on track when it reappeared.

As of mid-October CCD photometry was raising a big red flag. Even though V-band photometry showed a healthy comet brightening at a normal, or even above normal, rate, R-band photometry showed a comet that was barely brightening at all. It was if the comet had a split personality, increasing gas production but little increase in dust production. This divergence couldn’t last and visual and CCD observations over the past two weeks show that is hasn’t. Unfortunately the the comet’s brightness in V has now slowed down to match what we’ve been seeing in the R images.

All bets are off as to what ISON will do in the coming weeks. What seems to be certain is that the comet will not become a brilliant object pre-perihelion and may not even reach naked eye brightness prior to being lost in the glare of dawn.Will the comet experience a surge in brightness around perihelion, will it split, disintegrate, or just solider on as a healthy but intrinsically faint comet? We can wait and watch.

ISON starts the month in Leo at 0.98 AU from the Sun and 1.23 AU from Earth. It will travel the length of Virgo and Libra before encountering the Sun near the head of Scorpius. Depending on how bright the comet gets, observers with clear skies and horizons may be able to follow the comet to within a week or less of perihelion. If the comet becomes brighter than ~ -4 at perihelion it may even be visible to telescopic observers during the day for a few hours around perihelion. Assuming it survives perihelion, the comet will once again become visible in early December.

InboundComets

2P/Encke [T = 2013 Nov 21, q = 0.34 AU]

Encke has the shortest known period of any comet at 3.3 years. Since it was first seen in 1786, the comet has been observed to orbit the Sun over 60 times. On October 16/17 it reached a minimum distance of 0.48 AU from Earth. With perihelion on November 21, Encke will also be quickly descending into the glare of dawn as it races along the length of Virgo into Libra.

At the start of the month, Encke will be 0.62 and 0.60 AU from the Sun and Earth, respectively. Most observers will lose sight of the comet by mid-month as the comet drops to within ~0.4 AU of the Sun. As of late October, the comet was between magnitude 7.5 and 8.0 and it should reach magnitude 5.5 to 6.0 by mid-month.

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

Perhaps the brightest comet in the sky right now (magnitude 7.0 to 7.5) is a relatively new discovery. On September 7 Terry Lovejoy, an amateur astronomer from Queensland, Australia, discovered comet C/2013 R1 (Lovejoy) on CCD images taken with a HyperStar equipped 8″ SCT. The comet will close to within 0.40 AU of Earth on November 19/20 and perihelion on December 22 at a distance of 0.81 AU from the Sun. Unlike ISON, Lovejoy is a dynamically old comet and has been rapidly brightening since discovery. If its brightening rate continues the comet may be a borderline naked eye object by the end of the month at magnitude 5.0 to 6.0 when it will be 0.91 and 0.41 AU from the Sun and Earth. The comet starts the month in Cancer and quickly traverses Lynx, Ursa Major, Canes Venatici, before ending the month in northern Boötes.

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

Comet LINEAR was discovered back on December 8, 2012 at a faint 19th magnitude. The comet has always appeared intrinsically faint and was never expected to get much brighter than ~12th magnitude when it reaches perihelion early next year. Imagine the surprise of CCD observer Hidetaka Sato when he found the comet nearly six magnitudes brighter than predicted on Oct. 20. Like a miniature version of Comet Holmes in 2007, the comet currently sports a rapidly expanding shell of dust with evidence of jets and other coma features.

The comet is a morning object low in the northeastern sky as it moves slowly eastward from Coma Berenices through southern Boötes. Recent visual estimates place it between magnitude 7.5 and 8.5. Though the comet’s total magnitude may change little over the next few weeks, the surface brightness of the coma will decrease as the coma expands making the comet harder to see with time. With perihelion 3-4 months away, additional outbursts are definitely possible.

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 HIGHLIGHTS FOR OCTOBER 2013

2013-October-04

By the end of October as many as 4 comets may be brighter than 10th magnitude. With three still inbound, they will be even better next month.

Comet Spotlight

C/2012 S1 (ISON)

No question about it, Comet ISON (T = 2013 Nov 28, q = 0.01 AU) is the comet everyone is waiting for. Whether ISON will be the ‘Comet of the Century’ or even the ‘Comet of the Year’ remains to be seen. Visual and V-band CCD images from early October show the comet to be around magnitude 11.5. There has been much discussion on various comet related lists about whether the comet is brightening or even starting a terminal fade. Observations by your Comet Section co-coordinator show the split personality of the comet with V-band measurements showing a rapidly brightening comet and R-band images showing little brightening over the past few weeks. R-band samples primarily dust while V-band sees a heavy gas component so perhaps the comet is becoming more gas-rich, or dust-poor depending on your view.

ISON is a morning object as it moves through Leo only a few degrees north of Mars. We should expect it to brighten from its current magnitude 11.5 to around magnitude 8 or 9 by the end of the month. At the start of October the comet was located 1.65 AU from the Sun and 2.15 AU from Earth. By month’s end it will be 1.02 AU from the Sun and 1.26 AU from Earth.

It is still too early to say with any certainty what the ultimate brightness of ISON will be at perihelion, or even if it will survive to see perihelion for that matter. The Comet Section requests that ALPO observers make a concerted effort to observe Comet ISON as soon and as often as possible. Please visual magnitude estimates, drawings and images to the undersigned. We would also like to receive any FITS images in order to obtain standard photometry.

Inbound Comets

2P/Encke

There are two other inbound comets that should brighten enough to be seen without imaging equipment. Comet 2P/Encke (T = 2013 Nov 21, q = 0.34 AU) has the shortest known cometary period at 3.3 years. Since it was first seen in 1786, the comet has been observed to orbit the Sun over 60 times. The comet is starting the month at 1.5 AU from the Sun and ends the month 0.64 AU out. Its geocentric distance reaches a minimum of 0.48 AU on October 16/17. The most recent visual observations place the comet between magnitude 9.5 and 11.5. The large scatter in estimated brightness is likely due to the comet having a very large, low surface brightness coma which is typical of Encke. The comet should continue to rapidly brighten this month and be around magnitude 7 by the end of the month. Encke is also a morning object as it speeds through the constellations of Auriga, Lynx and Leo Minor. We request ALPO observers make a concerted effort to observe Comet Encke during the next few months leading up to its perihelion.

C/2013 R1 (Lovejoy)

This one is a new discovery. On September 7 Terry Lovejoy, an amateur astronomer from Queensland, Australia, discovered comet C/2013 R1 (Lovejoy) on CCD images taken with a HyperStar equipped 8″ SCT. The comet will close to within 0.40 AU of Earth on November 19/20 and perihelion on December 22 at a distance of 0.81 AU from the Sun. Located at distances of 1.61 AU from the Sun and 1.28 AU from Earth, the comet is currently being observed at magnitude 10.5. It is very possible Lovejoy may become a borderline naked eye visible comet in late November/early December at the same time that ISON is also (hopefully) visible to the naked eye as well. FYI, both comets will be morning objects. We ask that ALPO observers also make observations of Comet Lovejoy.

Outbound Comets

C/2012 V2 (LINEAR)

This one is only for southern hemisphere observers. C/2012 V2 (T = 2013 Aug 16, q = 1.45 AU) is currently between magnitude 9.0 and 10.0. It should fade by a magnitude by the end of the month as it moves from 1.59 to 1.80 AU from the Sun and 2.09 to 2.27 AU from Earth. The comet will be moving through Antila, Vela and Centaurus this month.

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.

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 SEPTEMBER 2013

2013-September-04

Comet action starts to really pick up this September. Though only one comet is currently brighter than magnitude 10, the ’stars’ of the Fall are rapidly brightening and can be followed via CCD imaging and large aperture visual observing.

C/2012 V2 (LINEAR)

C/2012 V2 is a nice surprise comet that has become much brighter than expected. Observations over the past few weeks show it to be between magnitude 8 and 9. It reached perihelion on August 16 at a distance of 1.45 AU from the Sun. Even though it is past perihelion it should only fade slowly this month, still being brighter than 9.0 to 9.5 by the end of the month. The comet is only visible from the Southern Hemisphere as it tracks southeastward along the border of Hydra and the constellations of Puppis, Pyxis and Antlia.

Inbound Comets

C/2012 S1 (ISON)

After passing solar conjunction this summer, Comet ISON (T = 2013 Nov 28, q = 0.01 AU) is once again observable. There has been much discussion on how bright the comet really is with magnitude estimates that range from 11th to 15th magnitude. It seems the consensus is around magnitude 13. A big reason for the discrepancy was ISON’s location very low in the eastern sky during dawn in August. This month the comet will be observable at a more convenient elevation before the start of dawn. Hopefully we’ll have a better understanding of its brightness over the next few weeks.

The comet will be a morning object this month as it moves from just north of the Beehive Cluster in Cancer and into Leo by month’s end. Assuming the comet is around magnitude 13 at the start of the month, it should brighten to between magnitude 11.5 and 12.0 by the end of the month. On the 1st ISON will be 2.18 AU from the Sun and 2.97 AU from Earth. By the end of the month the comet will be 1.65 AU from the Sun and 2.15 AU from Earth. An added bonus for early morning observers will be the comet’s proximity to Mars at the end of the month. ISON will pass within 0.07 AU of Mars on October 1 resulting in the comet being located within a few degrees of Mars for a few days. Many of the spacecraft on and around Mars will be imaging the comet at that time.

2P/Encke

If ISON is a new comet inbound for the first time in billions of years, the other bright comet of the Fall is its opposite. Comet 2P/Encke (T = 2013 Nov 21, q = 0.34 AU) has the shortest known cometary period at 3.3 years. Since it was first seen in 1786, the comet has been observed to orbit the Sun over 60 times. The comet is starting the month at 1.58 AU from the Sun and ends the month 1.15 AU out. Its geocentric distance closes from 1.16 to 0.60 AU. The most recent visual observations place the comet around magnitude 14 which agrees well with its behavior in the past. The comet should continue to rapidly brighten this month and be around magnitude 12.6 on the 11th, 11.3 on the 21th and 9.7 by October 1 as it leaves Perseus and traverses Auriga. We also request ALPO observers make a concerted effort to observe Comet Encke during the next few months leading up to its perihelion.

C/2012 K1 (PANSTARRS)

While ISON may be getting all of the headlines due to the possibility of it becoming a brilliant object, C/2012 K1 is actually a much brighter comet intrinsically (T = 2014 Aug 27, q = 1.06 AU). Based on recent CCD observations C/2012 K1 is intrinsically ~2 magnitudes brighter than ISON and very similar in brightness to C/2011 L4 (PANSTARRS) at a similar distance from the Sun (5.2 AU). Current projections have it reaching 5-6th magnitude next summer which is impressive considering the comet will be located over 2 AU from Earth on the other side of the Sun at the time. We can only imagine how bright this comet would be if it came closer to Earth.

This month the comet decreases its heliocentric distance from 4.74 to 4.45 AU from the Sun. Even at this distance, it is ~13-14th magnitude and already showing significant jet activity.

Similar to ISON, K1 is a dynamically new comet. Such comets routinely brighten rapidly when far from the Sun only to see their rate of brightening slow, stall or even turn into a fading trend as they get closer to the Sun. Observers are encouraged to monitor K1 as it nears the heliocentric distances when C/2011 L4 and C/2012 S1 experienced their change in brightening.

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.

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 August 2013

2013-July-30

Here in Tucson (the home of your Comet Section C0-coordinator), August marks the end of the observing year. In most places, observing slows down in the winter due to bad weather and the cold. But in usually sunny southern Arizona, the summer is the time when our mirror covers stay on. For almost two months, the monsoon rains force the complete shutdown of many professional telescopes and most amateur ones as well. But by September the rains are moving on and we start planning the upcoming observing season.

In a way, the field of comet observation is having a similar month to Tucson. The bright comets of the Spring are now receding from view while we await the “hopefully” rapid brightening of this Fall’s cometary duo.

C/2012 F6 (Lemmon)

As has been the case for the past two months, Comet Lemmon remains the brightest comet in the sky and the only comet that is a relatively easy object for visual observation. Now over 4 months past perihelion (T = 2013 Mar 24, q = 0.73 AU), the comet continues its steady fading as it recedes from 1.88 to 2.70 AU from the Sun and 2.04 to 2.38 AU from Earth this month. The comet should be magnitude 9.7 on the 1st, 10.0 on the 11th, 10.3 on the 21st and 10.6 at the end of the month. Lemmon is a northern circumpolar object and starts the month in Cepheus before entering Draco.

C/2011 L4 (PANSTARRS)

Comet PANSTARRS is much faded from its March glory days when it peaked at 1st magnitude (T = March 10, q = 0.30 AU). August sees the comet moving south through the constellation of Bootes. Based on recent magnitude estimates the comet should fade from magnitude 11.4 to 12.3. Though this will probably be the last month this comet will be listed in the Comet Highlights, CCD and large aperture visual observers are encouraged to keep track of it as it slowly fades over the coming months and years.

Inbound Comets

C/2012 S1 (ISON)

I wish I had some real news to report about Comet ISON (T = 2013 Nov 28, q = 0.01 AU). The supposed ‘Comet of the Century’ has been hanging out too close to the Sun since mid-June to be seen from Earth. When last spotted it was around 15th magnitude. Unfortunately it’s been stuck at 15th magnitude since January. Of course, that’s 15th apparent magnitude (the brightness the comet appears to us on Earth). Intrinsically, the comet has actually faded by ~2 magnitudes since January.

Though this doesn’t bode well for a -8, -12 or -16 magnitude comet as reported in the press, comets fading or at least stalling in their brightening is not unheard of. In fact it is fairly common for dynamically new comets making their first trip into the realm of the planets after billions of years. What is odd about ISON’s behavior is that it is experiencing its stall or fading so far out from the Sun. Most dynamically new comets are closer to the Sun when they ‘misbehave’ and most only see their rate of brightening slow down rather than go into reverse.

ISON will reappear in the morning sky this month as it transverses Cancer. Hopefully the first CCD observations will roll in around mid-month. By the end of the month the comet will still be low in the sky (~10 degrees up at the start of astronomical twilight for northern mid-latitude observers, southern comet watchers probably won’t be able to image ISON this month). It’s anyone’s guess as to how bright ISON will be when recovered. When last seen the comet was 3.7 AU from the Sun. It will be 2.42 AU from the Sun at mid-month and 2.18 AU at the end of the month. If the comet is imaged around the middle of the month, accurate photometry will give us a good clue as to what the comet has been up to since June. If it’s still only magnitude ~15.5 it means the comet has continued fading at the same rate as it has since the start of the year. If it is around magnitude 14.5 then the comet is intrinsically the same brightness as it was in early June. On the other hand if the comet is brighter than ~14.5 then it means the comet has started intrinsically brightening once again.

2P/Encke

If ISON is a new comet inbound likely for the first time in billions of years, the other bright comet of the Fall is its opposite. Comet 2P/Encke (T = 2013 Nov 21, q = 0.34 AU) is the comet with the shortest known period at 3.3 years. Since it was first sighted in 1786, the comet has been observed to orbit the Sun over 60 times. Even though the comet is starting the month only 1.94 AU from the Sun (that distance decreases to 1.57 AU at the end of the month), it is a late bloomer and may still be nearly inactive this month. In fact, the most recent observations place it around 19th magnitude. CCD imagers are encouraged to routinely image this comet over the next few months as it rapidly transforms from a 19th magnitude “asteroid” to a 6th or 7th magnitude “fuzzball” in late October.

C/2012 K1 (PANSTARRS)

While ISON may be getting all of the headlines due the possibility of becoming a brilliant object, C/2012 K1 is actually a much brighter comet intrinsically (T = 2014 Aug 27, q = 1.06 AU). Based on recent CCD observations C/2012 K1 is intrinsically ~2 magnitudes brighter than ISON and very similar in brightness to C/2011 L4 (PANSTARRS) at a similar distance from the Sun (5.2 AU). Current projections have it reaching 5-6th magnitude next summer which is impressive considering the comet will be located over 2 AU from Earth on the other side of the Sun at the time. We can only imagine how bright this comet would be if it came closer to Earth.

This August the comet decreases its heliocentric distance from 5.05 to 4.74 AU located over 5 AU from the Sun. Even at this distance it is ~14th magnitude and already showing significant jet activity.

As explained above in the ISON section, K1 is a dynamically new comet. Such comets routinely brighten rapidly when far from the Sun only to see their rate of brightening slow, stall or even turn into a fading trend as they get closer to the Sun. Observers are encouraged to monitor K1 as it nears the heliocentric distances when C/2011 L4 and C/2012 S1 experienced their change in brightening.

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.

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 JULY 2013

2013-July-6

This month’s ALPO Comet Highlights is a little late. It will also be short as the bright comets of the spring recede into the depths of the outer Solar System and the bright comets of the fall are still faint or too close to the Sun for observation.

The Section is 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.

C/2012 F6 (Lemmon)

Comet Lemmon remains the brightest comet in the sky. In fact, it is the only comet that is currently an easy object for small telescope visual users. Now ~3+ months past perihelion (T = 2013 Mar 24, q = 0.73 AU), the comet is fading as it moves from 1.88 to 2.30 AU from the Sun and 1.83 to 2.04 AU from Earth this month. If its current fading trend continues, the comet will be around magnitude 8.4 on the 1st, 8.7 on the 11th, 9.0 on the 21st and 9.3 at the end of the month. Lemmon is a northern circumpolar object moveing through the constellations Cassiopea and Cepheus.

C/2011 L4 (PANSTARRS)

Though the brightest comet of the year (so far…), PANSTARRS has faded quite a bit from its peak at 1st magnitude back in March (T = March 10, q = 0.30 AU). This month the comet moves south from Draco into Bootes as it fades from magnitude 10.3 to 11.4. It remains a spectacular sight in deep CCD images with a number of dust tails.

Inbound Comets

C/2012 S1 (ISON) and 2P/Encke

Comets ISON (T = 2013 Nov 28, q = 0.01 AU) and Encke (T = 2013 Nov 21, q = 0.34 AU) are predicted to become an easy naked eye comet and a borderline naked eye comet, respectively this November/December. This month, both comets are still faint and, in the case of ISON, too close to the Sun for observation.

C/2012 K1 (PANSTARRS)

ISON may be getting all of the headlines due to its extremely close approach to the Sun in late November and the possibility of reaching a brilliant apparent brightness but C/2012 K1 is a much brighter comet intrinsically (T = 2014 Aug 27, q = 1.06 AU). Current projections have it reaching 5-6th magnitude next summer. What is most impressive about this is that the comet will be located over 2 AU from Earth at the time. We can only imagine how bright this comet would be if it came closer to Earth.

This month the comet is still located over 5 AU from the Sun. Even at this distance it is ~14th magnitude and already showing significant jet activity. We would like CCD images and magnitude measurements in order to monitor this comet’s development.

C/2013 G5 (Catalina)

Comet Catalina is featured on the cover of the Summer 2013 issue of the Strolling Astronomer. Too bad it may not have survived long enough to appreciate the honor. Always intrinsically faint the comet never amounted to more than a diffuse object (T = 2013 Sep 1, q = 0.93 AU). The most recent images were taken in mid to late June. At that time the comet was only a ghost with almost no central condensation. Though a challenge, deep CCD users are encouraged to image this comet to see what, if anything, still remains.

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 JUNE 2013

The Comet Section would like to thank all the observers who have sent us their comet observations. Please keep the observations coming. For those of you who have been observing comets recently and have not submitted them to the Comet Section or to the ALPO Image Archive, please do so. An Image Gallery for the Comet Section has been created and is being populated with images.

At any time, there are usually 1 or more comets within reach of visual observers with small telescopes and a half dozen or more within reach of large telescopes. CCD observers can count on many tens of comets being visible to them. This report will concentrate on a few of the more interesting comets that are currently observable this month.

C/2012 F6 (Lemmon)

The brightest comet of the month is Comet Lemmon. It peaked at magnitude 4.5 when it passed perihelion on March 24 at a distance of 0.73 AU from the Sun. At that time the comet was located deep in the southern sky and wasn’t visible to northern observers. The comet has since moved north and is located in the morning sky against the stars of Andromeda. As the month progresses its northward motion will make it a circumpolar object for much of the Northern Hemisphere.

Observers are currently estimating its brightness around magnitude 7.0 to 7.5. Since the comet is moving away from the Earth and Sun it will fade to magnitude 8.0 to 8.5 by the end of the month. CCD images are still showing the comet to be gas-rich/dust-poor with a gas tail over a degree in length. Large aperture telescope images show not only the tail but also a number of near-nucleus jets.

On June 1 Lemmon is located 1.46 AU from the Sun and 1.75 AU from Earth, by mid-month it is 1.66 AU from the Sun and 1.77 AU from Earth and by the end of the month it will be 1.87 AU from the Sun and 1.83 AU from Earth.

C/2011 L4 (PANSTARRS)

Even though Comet Lemmon holds the rank of brightest comet in the sky, many observers seem to be ignoring it in favor of our second brightest comet, Comet PANSTARRS. This comet passed perihelion back on March 10th of this year at a relatively small perihelion distance of 0.30 AU from the Sun. At that time, it was as bright as magnitude ~+1.5. Though situated deep in the glow of twilight, visual observers were able to detect it with the naked eye and even see ~0.5-1.0 degrees of a tail. CCD imagers caught a more spectacular sight as the tail extended over a large range of position angles and contained a large number of striae.

By the end of May, the comet had faded to magnitude 7.5 to 8.5. What PANSTARRS currently lacks in brightness it more than makes up in tails, or more specifically its anti-tail. On May 26/27, the Earth passed through the plane of PANSTARRS’ orbit resulting in the appearance of a long thin anti-tail. In some images this feature stretches more than 8 degrees from the head of the comet. For examples see the following Comet Section Gallery images here, here, here and here (or just go to the C/2011 L4 folder of the Comet Section Image Gallery). The anti-tail should still be visible during the first half of June but will fade from view as the Earth moves out of the comet’s orbital plane.

The comet is currently a northern circumpolar object and starts the month a few degrees from Polaris. By the end of the month it is located in Draco north of the constellation Bootes. This will probably be the last month for easy observation of PANSTARRS in small telescopes as it should fade to magnitude 10-11 by month’s end. On June 1 it will be 1.84 AU from the Sun and 1.85 AU from Earth. By the end of the month it will be 2.29 AU from the Sun and 2.26 AU from Earth.

C/2012 L2 (LINEAR)

This comet is only visible to southern observers. Now a month past its May 9 perihelion (q=1.50 AU), Comet LINEAR has been reported as bright as magnitude 8.5-9.0. The comet seems to have rapidly brightened in the month or two prior to perihelion. It will be interesting to see if it maintains its current brightness or fades just as quickly as it brightened. Comet Linear’s distance from the Sun will increase from 1.54 to 1.64 AU and its distance from Earth will increase from 2.31 to 2.35 AU.

Inbound Comets

The following comets are inbound and though currently faint, have the potential to be interesting objects over the next few months. We ask that CCD and large telescope visual observers add them to your observing lists. Observations made as objects approach the Sun are very important to not only making predictions of their future brightness but also help researchers understand the processes and chemical species that drive their activity.

C/2012 S1 (ISON)

Dubbed by the press and even NASA PR as the ‘Comet of the Century’, Comet ISON is the most anticipated comet of the year. Some press articles and even a professional paper have predicted that the comet will reach magnitude -16 (brighter than the Full Moon) when it arrives at perihelion on November 28 of this year (Thanksgiving Day!). At that time the comet will only be 1.2 million km above the surface of the Sun (resulting in an apparent elongation of ~0.5 degrees from the Sun).

It is highly unlikely the comet will become that bright. For starters, that prediction assumes the comet will brighten at an ‘average’ rate for a long-period comet. Unfortunately there are two problems with that. All comets, and especially dynamically new comets like ISON, have a habit of not brightening at a steady rate or brightening at a slower than average rate. In the case of the above mentioned Comet PANSTARRS it ceased brightening for a number of months before perihelion. ISON is doing PANSTARRS one better (or worse in this case). Not only has it not brightened since January, it has actually faded intrinsically. As a result the comet which was as bright as magnitude 15 a few months ago is now only at 16th magnitude even though it is closer to the Sun and Earth.

Whether ISON will be a great comet, just a good comet, or completely disintegrate as it rounds the Sun is still to be seen. The first week or two of June mark the last opportunity to observe ISON before it gets too close to the Sun. The comet will once again be visible as a morning object in mid-August. We ask that CCD observers try to image ISON as long as possible before it sinks out of view. The comet starts the month 3.5 AU from the Sun in the constellation of Gemini.

C/2012 K1 (PANSTARRS)

Yet another Pan-STARRS find, C/2012 K1 is still 5.6 AU from the Sun at the start of June. It won’t reach perihelion for over a year (August 27, 2014 at 1.05 AU from the Sun). The comet is currently around 15th magnitude and is situated near the Hercules-Ophiuchus border. At perihelion the comet should be a nice binocular object though that will all depend on how it brightens. CCD images and large telescope visual estimates will allow us to better model this comet’s current and future activity levels.

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)

March 13, 2013

Comets PANSTARRS and Lemmon at their best

During the Spring of 2013, two comets will be visible to the naked eye.

Comet C/2011 L4 (PANSTARRS) is a bright 1st magnitude object sporting a bright dust tail. The comet reached perihelion at a distance of 0.30 AU from the Sun on March 10th and is currently at its brightest. After spending the last few months only visible from the Southern Hemisphere, the comet is now visible from Northern Hemisphere. Many observers have been able to observe the comet with the naked eye even though it is located at very low elevations against a bright twilight sky. Co-coordinator Carl Hergenrother was able to observe the comet as a faint star with a hint of a 0.1° tail on the evening of March 13 UT when the comet was only 3° above the horizon. Not until April will it be visible against a dark sky. It will become circumpolar by the end of April though it will have most likely faded to a faint naked eye object.

Image of Comet C/2011 L4 (PANSTARRS) and the Moon taken by Robert Lunsford from Chula Vista, CA, USA on the evening of March 12, 2013. The image is a 2-second exposure taken at f/3.5 with a Canon Power Shot S2 IS. Credit: Robert Lunsford.

The other naked eye comet is C/2012 F6 (Lemmon). Recent magnitude estimates place it at magnitude 4.5 to 5.0. With perihelion on March 24 at a distance of 0.73 AU from the Sun, the comet may brighten a few more tenths of a magnitude. CCD imagers find the comet to be gas-rich and appearing strikingly different from dust-rich Comet PANSTARRS. Lemmon is currently a Southern Hemisphere-only comet and will not be visible for northern observers until late April/early May when it emerges in the morning sky. By then the comet should have faded to magnitude 6.

Though not yet of naked eye brightness, the other big comet of the year is the so-called ‘Comet of the Century’, C/2012 S1 (ISON). Whether this comet becomes as spectacular as hoped this coming November/December is still to be seen. This Spring, ISON is well placed in the evening sky for CCD and large aperture visual observation. The comet is currently 15th magnitude. It should continue to brighten to 14th magnitude by the time it gets too close to Sun for easy observation in late May.

The ALPO Comet Section request observations of these and other comets, including images, drawings and magnitude estimates.

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