View source for Great January Comet of 1910

{{short description|Non-periodic comet}}
{{Use dmy dates|date=November 2025}}
{{Infobox comet
| name            = C/1910 A1<br>(Great Daylight Comet of 1910)
| image           = Comet 1910 A1.jpg
| caption         = C/1910 A1, the Daylight or Great January Comet, photograph from Lowell Observatory
| discoverer      = 
| discovery_site  = 
| discovery_date  = 12 January 1910
| designations    = 1910 I, 1910a
| orbit_ref       = {{r|barycenter}}
| epoch           = 9 January 1910 (JD 2418680.5)
| observation_arc = 82 days
| obs             = 25
| semimajor       = ~440 [[Astronomical Unit|AU]] (epoch 2000)
| perihelion      = {{Convert|0.12896|AU|e6km|abbr=unit|lk=off}}
| aphelion        = ~1150 AU (inbound)<br/>~900 AU (outbound)
| period          = ~9,200 years (outbound)
| eccentricity    = 0.99978
| inclination     = 138.78°
| physical_ref    = {{r|Fernández_2012}}
| mean_radius     = {{cvt|1.67|km|mi}}{{efn|Calculated mean radius using the formula: <math>\log_{10}\,(\,R\,)\ =\;0.9 +\;0.13 (\,H\,)</math>{{r|Fernández_2012}}<br>Where <math>\,H\,</math> is the comet's absolute total magnitude (M1)}}
| M1              = 5.2
| M2              = 
| magnitude       = –5.0<br>{{small|(1910 apparition)}}{{r|ICQ2}}
| last_p          = 17 January 1910
| next_p          = 
}}
The '''Great January Comet of 1910''', formally designated '''C/1910 A1''' and often referred to as the '''Daylight Comet''',<ref name="moore178">{{Citation |last=Moore |first=P. |title=Space: The First 50 Years |location=New York |publisher=Sterling |year=2007 |page=178 |isbn=978-1-4027-5208-7 }}.</ref> was a [[comet]] which appeared in January 1910. It was already visible to the [[naked eye]] when it was first noticed, and many people independently "discovered" the comet. At its brightest, it outshone the planet [[Venus]], and was possibly the brightest comet of the 20th century.{{r|ICQ2}}

== Observational history ==
=== Discovery ===
The comet came to [[solar conjunction]] about 1 degree from the Sun on 17 December 1909 but was still about 1 AU from the Sun. In January the comet brightened rather suddenly, and was initially visible from the [[Southern Hemisphere]] only. A number of individuals claimed "discovery", but the comet is thought to have been first spotted by diamond miners in the [[Transvaal Colony|Transvaal]] before dawn on 12 January 1910, by which time it was already a prominent naked-eye object of [[apparent magnitude]] −1.0 with a [[declination]] of −29 (i.e. best seen from the Southern Hemisphere).{{r|ICQ2}}

The first person to study the comet properly was Scottish astronomer [[Robert T. A. Innes]] at the Transvaal Observatory in [[Johannesburg]] on 17 January, after having been alerted two days earlier by the editor of a Johannesburg newspaper.

The comet reached [[perihelion]] on 17 January and was at that time visible in daylight with the unaided eye, having a magnitude of −5.0 due to the [[forward scatter]]ing of light.{{r|ICQ2}} It came to solar conjunction a second time on 18 January 1910.<ref name=conjunction/> Following perihelion, it declined in brightness but became a spectacular sight from the [[Northern Hemisphere]] in the evening twilight, its noticeably curved tail reaching up to 50 degrees by early February.{{r|ICQ2}}

=== Halley's Comet and the Daylight Comet ===
The year 1910 saw considerable media interest in the predicted return of [[Halley's Comet]], which reached perihelion on 20 April. The appearance of the Daylight Comet several months earlier therefore came as something of a surprise, and made an extremely strong impression on an expectant public; when Halley's Comet returned again in 1986, many older people's accounts of having seen it in 1910 clearly referred to the Daylight Comet instead.<ref name=burnham184>{{Citation |last1=Burnham |first1=R. |name-list-style=amp |last2=Levy |first2=D. |title=Great Comets |location=New York |publisher=[[Cambridge University Press]] |year=2000 |page=[https://archive.org/details/greatcomets00burn/page/184 184] |isbn=0-521-64600-6 |url-access=registration |url=https://archive.org/details/greatcomets00burn/page/184 }}.</ref>

Owing to a "telephonic error", the comet was initially reported as being named Drake's Comet, though once the error was realised the press afterwards referred to it as the Daylight Comet or Sunset Comet, as no single individual was credited with its discovery.<ref>{{cite news |title=Not Much is Known of Daylight Comet. Greenwich Astronomer Thinks It Has Never Been Seen Before and May Never Be Again |url=https://www.nytimes.com/1910/01/30/archives/not-much-is-known-of-daylight-comet-greenwich-astronomer-thinks-it.html |quote=Outside politics the recently discovered daylight comet has been the chief topic of the week in England. It appears that the name of "Drake's comet", by which it has been generally known here, was given by mistake owing to a telephonic error, and it now goes by the name of the daylight or sunset comet. |work=[[New York Times]] |date=30 January 1910 |access-date=14 November 2009 }}</ref>

=== Panic ===
Newspapers in various cities reported people having been scared by the appearance of the comet.<ref>The Baltimore Sun (Baltimore, Maryland) 23 April 1910, Sat Page 1</ref> The Morning Post of [[Camden, New Jersey]] reported that similar scares happened in past years when comets had been seen.<ref>The Morning Post (Camden, New Jersey) 11 May 1910, Wed Page 6</ref> In [[Korea]] many thought the comet would kill them all off. Some stopped going to work, just ate and drank and waited for the world to end.<ref>{{Cite web|date=10 November 2019|title=Daylight comet of 1910 portends end of Korean dynasty|url=https://www.koreatimes.co.kr/www/opinion/2021/10/721_278377.html|access-date=29 October 2021|website=koreatimes|language=en}}</ref>

== See also ==
* [[C/1975 V1 (West)]]
* [[C/2006 P1 (McNaught)]]
* [[C/2023 A3 (Tsuchinshan–ATLAS)]]

== References ==
=== Notes ===
{{Notelist}}

=== Citations ===
{{Reflist|refs=

<ref name=barycenter>{{cite web
  |title=Barycentric Osculating Orbital Elements for Comet C/1910 A1 (Great January comet)
  |author=[[JPL Horizons On-Line Ephemeris System|Horizons]] output
  |url=https://ssd.jpl.nasa.gov/horizons_batch.cgi?batch=1&COMMAND=%271910+A1%27&TABLE_TYPE=%27ELEMENTS%27&START_TIME=%271800-01-01%27&STOP_TIME=%272000-01-01%27&STEP_SIZE=%27200%20years%27&CENTER=%27@0%27&OUT_UNITS=%27AU-D%27
  |access-date=6 September 2021}} (Solution using the Solar System [[Barycenter]]. Ephemeris Type:Elements and Center:@0)</ref>

<ref name=conjunction>{{cite web
  |title=C/1910 A1 solar conjunction on 18 Jan 1910
  |author=[[JPL Horizons On-Line Ephemeris System|Horizons]] output
  |url=https://ssd.jpl.nasa.gov/horizons_batch.cgi?batch=1&COMMAND=%271910+A1%27&START_TIME=%271910-01-18%27&STOP_TIME=%271910-01-19%27&STEP_SIZE=%272%20hours%27&QUANTITIES=%2720,23%27
  |access-date=6 September 2021}}</ref>

<ref name="Fernández_2012">{{cite journal
| author1= J. A. Fernández
| author2= A. Sosa
| title= Magnitude and size distribution of long-period comets in Earth-crossing or approaching orbits
| journal= Monthly Notices of the Royal Astronomical Society
| year= 2012
| volume= 423
| issue= 2
| pages= 1674–1690
| doi= 10.1111/j.1365-2966.2012.20989.x
| doi-access= free | arxiv= 1204.2285
}}
</ref>

<ref name="ICQ2">{{cite web
| author1= J. E. Bortle
| title= The Bright Comet Chronicles
| url= http://www.icq.eps.harvard.edu/bortle.html
| website= International Comet Quarterly
| year= 1998
| access-date= 18 November 2008 }}
</ref>

}}

== External links ==
{{Commons category}}
*[http://ssd.jpl.nasa.gov/?great_comets Donald Yeomans, "Great Comets in History". (Accessed 5/6/08)]
*[http://www.skyandtelescope.com/astronomy-news/the-great-daylight-comet-of1910/ The Great Daylight Comet of 1910], by John W. Bortle, Sky and Telescope
*{{JPL small body|name=C/1910 A1|id=1000967}}

{{Comets}}
{{Authority control}}

{{DEFAULTSORT:1910 A1}}
[[Category:Non-periodic comets]]
[[Category:Sungrazing comets]]
[[Category:Great comets]]
[[Category:1910 in science|Great January Comet Of 1910]]
[[Category:Astronomical objects discovered in 1910|19100112]]