17P/Holmes

Infobox Comet
name=17P/Holmes


discovery_date=November 6, 1892
designations=1892 V1; 1892 III; 1892f; 1899 L1; 1899 II; 1899d; 1906 III; 1906f; 1964 O1; 1964 X; 1964i; 1972 I; 1971b; 1979 IV; 1979f; 1986 V; 1986f; 1993 VII; 1993i
epoch=October 27, 2007 (JD 2454400.5)
semimajor=3.618414 AU
perihelion=2.053218 AU
aphelion=5.183610 AU
eccentricity=0.432564
period=6.882994 a
inclination=19.1126°
last_p=May 4, 2007
next_p=March 22, 2014

17P/Holmes is a periodic comet in our solar system, discovered by the British amateur astronomer Edwin Holmes on November 6, 1892. In only 42 hours in October 2007, the comet brightened from a magnitude of about 17 to about 2.8. This represents a change of brightness by a factor of about half a million and is the largest known outburst by a comet.

On November 9, 2007 the coma, the thin dissipating dust ball around the comet, was found to be the largest object in the solar system, with a diameter greater than that of the Sun.cite web |last=Jewitt |first=David |date=2007-11-09 |url=http://www.ifa.hawaii.edu/faculty/jewitt/holmes.html |title=Comet Holmes Bigger Than The Sun |publisher=Institute for Astronomy at the University of Hawaii |accessdate=2007-11-17] (Though by Solar System standards, the mass of the comet is minuscule.)

The comet remained visible in February 2008 though it had become a challenging target at about magnitude +5 in the constellation Perseus. It had expanded to greater than 2 degrees of arc as seen from the Earth, and thus had very little surface brightness.

Discovery

Comet 17P/Holmes was discovered by Edwin Holmes on November 6, 1892 while he was conducting regular observations of the Andromeda Galaxy (M31). Its discovery in 1892 was made because of and during magnitude changes similar to the 2007 outburst. 17P/Holmes brightened to an approximate magnitude of 4 or 5 before fading from visibility over a period of several weeks.Editors. " [http://www.skyandtelescope.com/observing/home/10775326.html Comet Holmes Stays Bright, Enlarges in the Evening Sky] ", "Sky and Telescope", 27 October 2007. Retrieved 29 October 2007.]

The comet's discovery was confirmed by Edward Walter Maunder (Royal Observatory, Greenwich, England), William Henry Maw (England), and Kidd (Bramley, England) and independent discoveries were made by Thomas David Anderson (Edinburgh, Scotland) on November 8 and by Mike Brown , (Wilkes) , (USA) and by John Ewen Davidson (Mackay, Queensland, Australia) on November 9.Davidson, J. E. " [http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1890Obs....13..247D&db_key=AST&data_type=HTML&format=&high=44b52c369016885 Comet e, 1889] ," "The Observatory", July 1890, Vol. 13, pp. 247. Retrieved 27 October 2007.]

The first calculations of the elliptical orbits of 17P/Holmes were done independently by Heinrich Kreutz and George Mary Searle. Additional orbits eventually established the perihelion date as June 13 and the orbital period as 6.9 years. These calculations proved that the comet was not a return of 3D/Biela.

The 1899 and 1906 appearances were observed, but the comet was lost after 1906 until recovered on July 16, 1964 by Elizabeth Roemer (US Naval Observatory, Flagstaff, Arizona, USA). Aided by the computer predictions of Brian G. Marsden, the comet has been observed on every subsequent return.

2007 outburst

Between October 23–24, 2007, Comet Holmes grew much brighter, going from about magnitude 17 to about magnitude 2.8 in just 42 hours.Gunn, Angela. " [http://blogs.usatoday.com/techspace/2007/10/flash-news-flas.html Flash News Flash!] ," "USA Today" Tech Space, 24 October 2007. Retrieved 25 October 2007.] cite journal |url=http://www.skyandtelescope.com/observing/home/10775326.html |accessdate=2007-10-25 |journal=Sky & Telescope |author=Roger W. Sinnott |date=October 24, 2007 |title=Comet Holmes Undergoes Huge Outburst] The first person reportedly to notice a change was J. A. Henríquez Santana on Tenerife in the Canary Islands; minutes later, Ramón Naves in Barcelona noticed the comet at magnitude 7.3. It became easily visible to the naked eye as a bright yellow "star" in PerseusFischer, Daniel. " [http://www.astro.uni-bonn.de/~dfischer/mirror/306.html Incredible comet eruption: from under 17th to 3rd magnitude in hours!] ," "The Cosmic Mirror", #306, 24 October 2007. Retrieved 25 October 2007.] [http://www.spaceweather.com/images2007/24oct07/skymap_north_holmes.gif?PHPSESSID=u4ckv3guss7diulg57tt3nc281 Sky
] , Northeast, after sunset, "Spaceweather.com". Retrieved 28 October 2007] , and by October 25 17P/Holmes appeared as the third brightest "star" in that constellation.

While large telescopes showed fine-scale cometary details, naked-eye observations gave a view similar to that of a star until October 26. After that date, 17P/Holmes began to appear more comet-like to naked-eye observers. During the comet's outburst, its orbit took it to near opposition with respect to Earth, and since comet tails point away from the Sun, Earth observers were looking nearly straight down along the tail of 17/P Holmes, making the comet appear as a bright sphere.

Based on orbital computations and luminosity before the 2007 outburst, the comet's nucleus was estimated at 3.4 km.Primary measurements, Chris L. Peterson [http://www.cloudbait.com/gallery/comet/holmes.html Cloudbait Observatory, Colorado] , The coma size values plotted at the bottom of this page are primary measurements. They were obtained using conventional methods: individual short CCDs images were made in order to avoid saturation, and these were then calibrated with bias, flat, and dark frames and summed to increase the image dynamic range. Each stacked image (for the 5 nights of data) was astrometrically calibrated (using Pinpoint) for scale, and the intensity profile of the coma measured with a standard tool (in this case, the line profile tool in MaximDL). The resulting profiles were exported to Excel, normalized to the same gain, and the width measured against the noise floor. The best reference is the plotted data itself.] In late October 2007 the coma's diameter increased from 3.3 arcminutes to over 13 arcminutesPrimary measurements, (see luminosity graph; bottom of page) [http://www.cloudbait.com/gallery/comet/holmes.html Cloudbait Observatory, Colorado] ] , about half the diameter that the Moon subtends in the sky. At a distance of around 2 AU, this means that the true diameter of the coma swelled to over 1 million km2 AU×(~150 Gm/AU)×sin(13 arcmin) ≈ 1.1 million km] , or about 70% of the diameter of the Sun. By comparison, the Moon is 380,000 km from Earth. Therefore, during the 2007 outburst of Comet Holmes the coma was a sphere wider than the diameter of the Moon's orbit around Earth. On 2007 November 9, the coma had dispersed to an area larger than the sun, briefly giving it the largest extended atmosphere in the solar system. [cite web |last=Britt |first=Robert |date=2007-11-15 |url=http://www.space.com/spacewatch/071115-comet-holmes-size.html |title= Incredible Comet Bigger than the Sun |publisher=Space.com |accessdate=2008-04-30]

The cause of the outburst is not definitely known. The huge cloud of gas and dust may have resulted from a collision with a meteoroid, or, more probably, from a build-up of gas inside the comet's nucleus which eventually broke through the surface. [ [http://news.bbc.co.uk/1/hi/sci/tech/7070108.stm "Comet Holmes brightens in retreat"] , BBC NEWS, 30 October 2007]

[
elliptical orbit between Mars and Jupiter. [ [http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=17P;orb=1 Nasa 3D simulation of orbit for 17P/Holmes] (Java Applet)] The comet was closest to the sun on May 4, 2007.]

Notes

External links

* [http://www9.ocn.ne.jp/~comet/pcmtn/0017p.htm 17P at Kazuo Kinoshita's Comets]
* [http://starrymirror.com/cometholmesquickfacts.htm Quick Facts About Comet Holmes]
* [http://www.aerith.net/comet/catalog/0017P/index.html 17P at Seiichi Yoshida's Comet Catalog]
* [http://realworldnumbers.wordpress.com/2007/10/26/hunting-for-comet-holmes-at-home/ Simple Instructions on How to Find Comet Holmes] Instructions for the Amateur based around Toronto or New York.
* [http://www.space.com/spacewatch/071025-comet-holmes.html "Obscure Comet Brightens Suddenly"]
* [http://www.astronomia.pl/english/index.php?w=1&id=97 Evolution of Comet 17P/Holmes]
* [http://demonstrations.wolfram.com/EnigmaticCometHolmes/ Enigmatic Comet Holmes] by Jeff Bryant, The Wolfram Demonstrations Project.