View source for C/2011 L4 (PanSTARRS)

{{Short description|Non-periodic comet}}
{{redirect|Comet PANSTARRS|the Hawaii telescope facility|Pan-STARRS|other comets discovered by "PANSTARRS"|List of Pan-STARRS discoveries}}
{{Use dmy dates|date=April 2014}}
{{Infobox comet
| name           = C/2011 L4 (PanSTARRS)
| image          = C 2011 L4 PanSTARRS.jpg
| caption        = Image of Comet PanSTARRS by Gingin Observatory
| discoverer     = [[Pan-STARRS]]
| discovery_date = 6 June 2011
| orbit_ref      = <ref>{{cite web |title=C/2011 L4 (PANSTARRS) |url=https://ssd.jpl.nasa.gov/tools/sbdb_lookup.html#/?sstr=2011L4 |website=Small-Body Database Lookup |publisher=ssd.jpl.nasa.gov |access-date=16 June 2024}}</ref>
| epoch          = 20 Mar 2012<br/>([[Julian day|JD]] 2456006.5)
| observation_arc= 3.27 years
| obs            = 5413
| orbit          = [[Oort cloud]]
| aphelion       = 68000 AU (inbound)<ref name=barycenter/><br/>4500 AU (outbound)
| perihelion     = 0.30161 [[Astronomical unit|AU]] (q)
| eccentricity   = 1.000087
| period         = Millions of years (inbound)<br/>~107,000 [[Julian year (astronomy)|yr]]<br/>(outbound solution for [[Epoch (astronomy)|epoch]] 2050)<ref name=barycenter/>
| inclination    = 84.199[[degree (angle)|°]]
| Jupiter_moid   = 0.17 AU
| last_p         = 10 March 2013<ref name=jpldata/>
| max_speed={{convert|76.7|km/s|mph|abbr=on}}<ref name="perihelion-kms"/> 
}}

'''C/2011 L4 (PanSTARRS)''', also known as '''Comet PANSTARRS''', is a [[List of non-periodic comets|non-periodic]] [[comet]] discovered in June 2011 that became visible to the [[naked eye]] when it was near [[perihelion]] in March 2013.<ref name="skytel-Apr2012"/><ref name=kronk/> It was discovered using the [[Pan-STARRS]] telescope located near the summit of [[Haleakalā]], on the island of [[Maui]] in Hawaii. Comet C/2011 L4 probably took millions of years to come from the [[Oort cloud]]. After leaving the planetary region of the Solar System, the post-perihelion [[orbital period]] ([[Epoch (astronomy)|epoch]] 2050) is estimated to be roughly {{gaps|107|000}}&nbsp;[[Julian year (astronomy)|years]].<ref name=barycenter/> Dust and gas production suggests the [[comet nucleus]] is roughly {{convert|1|km|sp=us}} in diameter,<ref name="ScienceAtNASA"/> while based on the absolute nuclear magnitude and a geometric albedo of 0.04 the diameter of the nucleus is over {{convert|2.4|km|sp=us}}.<ref>{{cite journal |last1=Ferrín |first1=Ignacio |title=The location of Oort Cloud comets C/2011 L4 Panstarrs and C/2012 S1 ISON on a comet evolutionary diagram |journal=Monthly Notices of the Royal Astronomical Society |date=1 August 2014 |volume=442 |issue=2 |pages=1731–1754 |doi=10.1093/mnras/stu820|doi-access=free |hdl=10495/8143 |hdl-access=free }}</ref> A method based on coma magnitude decay function estimated the [[effective radius]] at 2.317 ± 0.190 km.<ref>{{cite journal |last1=Paradowski |first1=Mieczyslaw Leszek |title=A new method of determining brightness and size of cometary nuclei |journal=Monthly Notices of the Royal Astronomical Society |date=1 March 2020 |volume=492 |issue=3 |pages=4175–4188 |doi=10.1093/mnras/stz3597|doi-access=free }}</ref>

==Observational history==
[[File:Panstarrs-Nasagraphic-640.jpg|thumb|left|For [[Northern hemisphere]] observers, Comet PANSTARRS was near the crescent Moon on 12/13 March 2013.]]
Comet C/2011 L4 was still 7.9&nbsp;[[Astronomical unit|AU]] from the Sun<ref name=kronk/> with an [[apparent magnitude]] of 19 when it was discovered in June 2011.<ref name="MPEC2011-L33"/> By early May 2012, it had brightened to magnitude 13.5,<ref name="MPEC2012-J16"/> and could be seen visually when using a large amateur telescope from a dark site. In October 2012, the [[Coma (cometary)|coma]] (expanding tenuous dust atmosphere) was estimated to be about {{convert|120000|km|mi|abbr=off|sp=us}} in diameter.<ref name="Cerny"/> C/2011 L4 was spotted without optical aid on 7 February 2013 at a magnitude of ~6.<ref name="Seargent2013"/> Comet PANSTARRS was visible from both hemispheres in the first weeks of March,<ref name="visibility"/> and passed closest to Earth on 5 March 2013 at a distance of 1.09 [[Astronomical unit|AU]].<ref name=kronk/> It came to [[Apsis|perihelion]] (closest approach to the Sun) on 10 March 2013.<ref name=jpldata/> Original estimates predicted that C/2011 L4 would brighten to roughly [[apparent magnitude]] 0 (roughly the brightness of [[Alpha Centauri A]] or [[Vega]]). An estimate in October 2012 predicted that it might brighten to magnitude −4 (roughly equivalent to [[Venus]]).<ref name="Pina"/> In January 2013 there was a noticeable brightening slowdown that suggested that it may only brighten to magnitude +1.<ref name="Cerny2013"/> During February the brightness curve showed a further slowdown suggesting a [[Apsis|perihelion]] magnitude of around +2.<ref name=Yoshida/>

However, a study using the [[Secular phenomena|secular]] [[light curve]] indicates that C/2011 L4 had a "slowdown event" when it was 3.6&nbsp;AU from the Sun at a magnitude 5.6.<ref name=Ferrin2013/> The brightness increase rate decreased and the estimated magnitude at perihelion was predicted as +3.5. [[Halley's Comet|Comet Halley]] would be magnitude −1.0 at the same perihelion distance. The same study concluded that C/2011 L4 is very young and belongs to the class of "baby comets" (i.e. those with a photometric age of less than 4 comet years).<ref name=Ferrin2013/>

When C/2011 L4 reached perihelion in March 2013, the actual peak magnitude turned out to be around +1,<ref name=ICQ/> as estimated by various observers all over the planet. However, its low altitude over the [[horizon]] made these estimates difficult and subject to significant uncertainties, both because of the lack of suitable reference stars in the area and the need for differential [[atmospheric extinction]] corrections. As of mid-March 2013, due to the brightness of twilight and low elevation in the sky, C/2011 L4 was best seen in [[binoculars]] about 40 minutes after sunset.<ref name="Atkinson"/> On 17–18 March, C/2011 L4 was near the 2.8-magnitude star Algenib ([[Gamma Pegasi]]).<ref name="Earthsky"/> On 22 April, it was near [[Beta Cassiopeiae]].<ref name=Yoshida/> On 12–14 May, it was near [[Gamma Cephei]].<ref name=Astrobob/> C/2011 L4 continued moving North until 28 May. The comet may have had a sodium tail as [[Comet Hale–Bopp#Sodium tail|Comet Hale–Bopp]] had.<ref>[http://www.astrosurf.com/comolli/com39.htm Comet C/2011 L4 (PanSTARRS) with sodium tail - 15 March 2013]</ref>

==Gallery==
<gallery widths="200px" heights="160px">
File:PanSTARRs And Moon.jpg|Comet PANSTARRS as observed from Southern California, USA, about 3° east of the new crescent Moon
File:Comet C2011 L4 (PANSTARRS).png|Photo taken 12 March 2013 in [[Woodland Hills, Los Angeles]], USA.
File:Comet C2011L4 PanSTARRS 2013-03-24 in Russia.jpg|Comet C/2011 L4 (PanSTARRS) with a fan-shaped tail 2013-03-24 17:00UT in [[Special Astrophysical Observatory of the Russian Academy of Science]] near the village of Nizhny Arkhyz.
File:Comet Pan-STARRS.JPG|Photo taken 18 March 2013, at [[Orbetello]], Italy).
File:C-2011 Comet PanStarrs taken from the Norman Lockyer Observatory on 26th May 2013 by John Maclean.jpeg|Photo taken by John Maclean at the Norman Lockyer Observatory, Sidmouth, Devon.
</gallery>

==See also==
* [[C/2012 S1]]&nbsp;(ISON)&nbsp;– a highly anticipated comet that disintegrated near perihelion in November 2013.

==References==
{{Reflist
| refs =

<ref name="barycenter">{{cite web
  | author=[[JPL Horizons On-Line Ephemeris System|Horizons]] output
  | url=https://ssd.jpl.nasa.gov/horizons_batch.cgi?batch=1&COMMAND=%272011+L4%27&TABLE_TYPE=%27ELEMENTS%27&START_TIME=%271950-01-01%27&STOP_TIME=%272050-01-01%27&STEP_SIZE=%27100%20years%27&CENTER=%27@0%27&OUT_UNITS=%27AU-D%27
  | title=Barycentric Osculating Orbital Elements for Comet C/2011 L4 (PANSTARRS) }} Solution using the Solar System [[Barycenter]]. Ephemeris Type:Elements and Center:@0 (To be outside planetary region, inbound epoch 1950 and outbound epoch 2050)</ref>

<ref name="perihelion-kms">{{cite web
  |title=Horizons Batch for 2013-Mar-10 perihelion velocity
  |publisher=[[JPL Horizons On-Line Ephemeris System|JPL Horizons]]
  |url=https://ssd.jpl.nasa.gov/horizons_batch.cgi?batch=1&COMMAND=%272011+L4%27&START_TIME=%272013-03-10%2003:50%27&STOP_TIME=%272013-03-10%2005:30%27&STEP_SIZE=%271%20min%27&QUANTITIES=%2719,20,22,39%27
  |accessdate=2023-01-22}}</ref>

<ref name="skytel-Apr2012">{{cite web
  | date = 12 April 2012
  | title = Comet Pan-STARRS: Still on Track
  | publisher = [[Sky & Telescope]]
  | url = http://www.skyandtelescope.com/community/skyblog/observingblog/Comet-PanSTARRS-Still-on-Track-147166535.html
  | access-date = 12 April 2012
  | archive-url = https://web.archive.org/web/20131022151236/http://www.skyandtelescope.com/community/skyblog/observingblog/Comet-PanSTARRS-Still-on-Track-147166535.html
  | archive-date = 22 October 2013
  | url-status = dead
  }}</ref>

<ref name="MPEC2011-L33">{{cite web
  | date = 8 June 2011
  | title = MPEC 2011-L33 : COMET C/2011 L4 (PANSTARRS)
  | publisher = [[IAU Minor Planet Center]]
  | url = http://www.minorplanetcenter.net/mpec/K11/K11L33.html
  | access-date = 17 May 2012}} (CK11L040)</ref>

<ref name="MPEC2012-J16">{{cite web
  | date = 4 May 2012
  | title = MPEC 2012-J16 : OBSERVATIONS AND ORBITS OF COMETS
  | publisher = IAU Minor Planet Center
  | url = http://www.minorplanetcenter.net/mpec/K12/K12J16.html
  | access-date = 17 May 2012}}</ref>

<ref name=kronk>{{Cite web
  | first = Gary W
  | last = Kronk
  | author-link = Gary W. Kronk
  | title = C/2011 L4 (PANSTARRS)
  | url = http://cometography.com/lcomets/2011l4.html
  | access-date = 13 June 2012
  | archive-date = 5 April 2001
  | archive-url = https://web.archive.org/web/20010405095745/http://cometography.com/
  | url-status = bot: unknown
  }}()</ref>

<ref name=jpldata>{{cite web
 |title        = JPL Small-Body Database Browser: C/2011 L4 (PANSTARRS)
 |url          = http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2011L4
 |publisher    = [[Jet Propulsion Laboratory]]
 |access-date   = 12 June 2012
 |archive-url  = https://web.archive.org/web/20170316024426/http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2011L4
 |archive-date = 16 March 2017
 |url-status     = live
 |df           = dmy-all }}</ref>


<ref name="Cerny">{{cite web
 |date         = 7 October 2012
 |title        = Watching comet Panstarrs activity
 |publisher    = Robotic telescope FRAM
 |author       = Jakub Cerny
 |url          = http://gloria.fzu.cz/en/news/Sledujeme-v%C3%BDvoj-aktivity-komety-Panstarrs
 |access-date   = 8 October 2012
 |archive-url  = https://web.archive.org/web/20130314140227/http://gloria.fzu.cz/en/news/Sledujeme-v%C3%BDvoj-aktivity-komety-Panstarrs
 |archive-date = 14 March 2013
 |url-status     = dead
 |df           = dmy-all
}}</ref>

<ref name=Yoshida>{{cite web
  | last = Yoshida | first = Seiichi
  | title = C/2011 L4 ( PanSTARRS )
  | url = http://www.aerith.net/comet/catalog/2011L4/2011L4.html
  | work = www.aerith.net
  | access-date = 25 February 2013}}</ref>

<ref name="Seargent2013">{{cite web
  | date = 10 February 2013
  | title = L4 naked-eye and T5 faded 
  | publisher = comets-ml · Comets Mailing List
  | author = David Seargent
  | url = http://tech.groups.yahoo.com/group/comets-ml/message/20694
  | archive-url = https://archive.today/20130412050925/http://tech.groups.yahoo.com/group/comets-ml/message/20694
  | url-status = dead
  | archive-date = 12 April 2013
  | access-date = 10 February 2013}}</ref>

<ref name="visibility">
{{cite web
  | date = 5 March 2013
  | title = Map: when can you see comet PanSTARRS
  | author = Geert Barentsen
  | url = http://blog.barentsen.be/2013/03/05/map-when-can-you-see-comet-panstarrs/
  | access-date = 5 March 2013
  | archive-url = https://web.archive.org/web/20130310035648/http://blog.barentsen.be/2013/03/05/map-when-can-you-see-comet-panstarrs/
  | archive-date = 10 March 2013
  | url-status = dead
  | df = dmy-all
  }}</ref>

<ref name="Pina">{{cite web
  | date = 23 October 2012
  | title = UPDATE THE LIGHT VISUAL CURVE OF COMET C/2011 L4 PANSTARRS
  | publisher = COMETS & ASTROPHYSICAL
  | author = J.P.Navarro Pina
  | url = http://astrocometas.blogspot.de/2012/10/update-light-visual-curve-of-comet.html
  | access-date = 23 October 2012
  | archive-date = 28 January 2013
  | archive-url = https://web.archive.org/web/20130128033207/http://astrocometas.blogspot.de/2012/10/update-light-visual-curve-of-comet.html
  | url-status = dead
  }}</ref>

<ref name="Cerny2013">{{cite web
  | date = 12 January 2013
  | title = Comet Panstarrs brightening slowdown
  | publisher = comets-ml · Comets Mailing List
  | author = Jakub Cerny
  | url = http://tech.groups.yahoo.com/group/comets-ml/message/20415
  | access-date = 12 January 2013
  | archive-date = 10 February 2013
  | archive-url = https://web.archive.org/web/20130210154015/http://tech.groups.yahoo.com/group/comets-ml/message/20415
  | url-status = dead
  }}</ref>

<ref name=Ferrin2013>{{cite journal
  | last=Ferrin  | first = Ignacio
  | title = Secular Light Curves of Comets C/2011 L4 Panstarrs and C/2012 S1 ISON
  | publisher = University of Antioquia
  | year = 2013
  | arxiv = 1302.4621
  | bibcode =  2013arXiv1302.4621F}}</ref>

<ref name="Atkinson">{{cite web
  | date = 7 March 2013
  | title = Comet PANSTARRS
  | author = Stuart Atkinson
  | url = http://waitingforison.wordpress.com/comet-panstarrs/
  | access-date = 10 March 2013}}</ref>

<ref name="ICQ">{{cite web
  | title = Recent Comet Brightness Estimates
  | url = http://www.icq.eps.harvard.edu/CometMags.html
  | access-date = 15 March 2013}}</ref>

<ref name="Earthsky">{{cite web
  | title = Everything you need to know: How to see Comet PANSTARRS
  | publisher = Earthsky
  | author = Deborah Byrd
  | url = http://earthsky.org/space/comet-panstarrs-possibly-visible-to-eye-in-march-2013
  | access-date = 17 March 2013}}</ref>

<ref name=Astrobob>{{cite web
  | date = 3 May 2013
  | last = King | first = Bob
  | title = Comet PANSTARRS for die-hards
  | url = http://astrobob.areavoices.com/2013/05/05/comet-panstarrs-for-die-hards/
  | access-date = 5 May 2013}}</ref>

<ref name="ScienceAtNASA">{{cite web
  | date = 14 March 2013
  | title = ScienceCasts: Sunset Comet
  | author = ScienceAtNASA
  | website = [[YouTube]]
  | url = https://www.youtube.com/watch?v=f1cYfPrHoJw#t=120s
  | access-date = 17 March 2013}}</ref>

|2}}

==External links==
{{Commons category}}
* [http://cometography.com/lcomets/2011l4.html C/2011 L4 (PANSTARRS)] – Cometography.com by Gary W. Kronk
* [http://www.aerith.net/comet/catalog/2011L4/2011L4.html C/2011 L4 (PanSTARRS)] – Seiichi Yoshida @ aerith.net
* [https://web.archive.org/web/20130307084631/http://shadowandsubstance.com/march2013comet/Panstarrs.html C/2011 L4 (PanSTARRS) animated orbit diagram] – [http://shadowandsubstance.com/ Shadow & Substance]
* [https://web.archive.org/web/20121206070627/http://scully.cfa.harvard.edu/cgi-bin/returnprepeph.cgi?d=c&o=CK11L040 Elements and Ephemeris for C/2011 L4 (PANSTARRS)] – [[Minor Planet Center]]
* [http://spacedex.com/comet-pan-starrs/ The complete guide to viewing Comet PANSTARR]
* [http://twitpic.com/c407q5 The view STEREO-B will have of PanSTARRS in March] (Bill Thompson via Twitter account ''Sungrazing Comets'') / [http://stereo-ssc.nascom.nasa.gov/browse/2013/03/09/behind/hi1/512/20130309_111801_s7h1B.jpg C/2011 L4 on 2013-March-09]{{Dead link|date=November 2018 |bot=InternetArchiveBot |fix-attempted=yes }} (entering STEREO/SECCHI HI-1B field of view below the "2013")
* [http://remanzacco.blogspot.com/2012/05/update-on-comet-c2011-l4-panstarrs.html Update on comet C/2011 L4 (PANSTARRS)] – Remanzacco Observatory (18 May 2012)
* [http://twitpic.com/cajm3q Very quick high-resolution "first look" at PanSTARRS in STEREO HI-1B] / [http://sungrazer.nrl.navy.mil/index.php?p=images/panstarrs.gif 2013-March-10 GIF animation] / [http://twitpic.com/catqwz 2013-March-12 up close] (Twitter account ''Sungrazing Comets'')
* [https://www.youtube.com/watch?v=qXhGKsXEoZE Video of Comet Panstarrs seen from Paris]
* [http://astrobob.areavoices.com/2013/05/19/dont-let-comets-panstarrs-and-lemmon-out-of-your-sight-yet/ Don’t let Comets PANSTARRS and Lemmon out of your sight … yet] – AstroBob (19 May 2013)

{{Comets}}
{{2013 in space}}

{{DEFAULTSORT:C 2011 L4}}
<!--Categories-->
[[Category:Comets in 2013]]
[[Category:Astronomical objects discovered in 2011|20110606]]
[[Category:Non-periodic comets]]
[[Category:Oort cloud]]
[[Category:Discoveries by Pan-STARRS]]