17P/Holmes

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**17P/Holmes**
Discovery

Discovery date:	November 6, 1892
Alternate 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
Orbital characteristics ^A
Epoch:	October 27, 2007 (JD 2454400.5)
Aphelion distance:	5.183610 AU
Perihelion distance:	2.053218 AU
Semi-major axis:	3.618414 AU
Eccentricity:	0.432564
Orbital period:	6.882994 a
Inclination:	19.1126°
Last perihelion:	May 4, 2007
Next perihelion:	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.^[1] (Though by Solar System standards, the mass of the comet is minuscule.)

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

1 Discovery
2 2007 outburst
3 Notes
4 External links
- 4.1 Photographs

[edit] Discovery

1892 November 10, near the Andromeda galaxy

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.^[2]

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.^[3]

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.

[edit] 2007 outburst

On October 25 the comet looked liked a bright new star in the constellation of Perseus.

Between October 23–24, 2007, Comet Holmes grew much brighter, going from about magnitude 17 to about magnitude 2.8 in just 42 hours.^[4]^[5] 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.^[5] It became easily visible to the naked eye as a bright yellow "star" in Perseus^[6]^[7], and by October 25 17P/Holmes appeared as the third brightest "star" in that constellation.^[5]

While large telescopes showed fine-scale cometary details, naked-eye observations gave a view similar to that of a star until October 26.^[6] After that date, 17P/Holmes began to appear more comet-like to naked-eye observers.^[6] 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.^[8] In late October 2007 the coma's diameter increased from 3.3 arcminutes to over 13 arcminutes^[9], 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 km^[10], 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.^[1]^[11]

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.^[12]

[edit] Location of comet in 2007

Motion viewed from Earth The comet's retrograde path in Perseus during July 2007 – March 2008. (Dates given every 14 days)	Location of comet from Earth (45N, 8PM, Oct 30, 2007) The comet looks like a bright star in early evening, in the constellation Perseus and above the bright star Capella. In binoculars or a small telescope, it resembles a round fuzzy ball.
Motion viewed from space 17P/Holmes is a periodic comet in an inclined and elliptical orbit between Mars and Jupiter.^[13] The comet was closest to the sun on May 4, 2007, and has been moving slowly away from the sun in an elliptical orbit.

[edit] Composite gallery

Motion with expanding dust cloud A simulation showing the angular diameter of the expanding dust cloud for 120 days past the initial event on October 24. The surface brightness will continue to decrease over time.	Photo composite A composite of Comet Holmes photos showing the comet's size and motion in the constellation Perseus from October 25, 2007 through March 9, 2008.

[edit] Wide angle photo gallery

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January 12 2008 17P/Holmes
December 13 Comet 17P/Holmes and Geminid	December 1 Comet Holmes on 12/01/07 from San Francisco.
November 20 With Canon XTI 55 mm f5.6, ISO 1600 for 17" from San Francisco	November 4 (29mm wide) - Comet is at bottom center (see arrow)
October 31 (140mm) - Comet is in center
October 27 (Wide angle view: 9^ox7^o) Comet is in center right

[edit] Telescopic photo gallery

Date
Oct 25	Cloudbait Observatory, Guffey, Colorado^[14] (5.1" square)
Oct 26	6" (150mm) telescope Minneapolis, Minnesota	4.5" (114mm) telescope Flintstone, Georgia	3.5" (90mm) telescope	3.5" 90 mm telescope
Oct 27	14.5" (370mm) Dobson
Oct 29	from Montreal, Quebec with an 80 mm Refractor
Oct 30	19" reflector Torquay, UK	Vixen 80 mm f/7.5 refractor, Meade DSI camera Costa Mesa, CA	St. Paul's School (Concord, New Hampshire), Concord, New Hampshire.	200mm Tamron; Canon EOS350D, Singapore.
Oct 31	8" telescope + EOS400D Barcelona, Spain.	8" telescope + EOS400D Barcelona, Spain. Shows the comet movement over the stars background for 50 minutes. Changes on brightness are due to different exposure times on each image.
Nov 1	80mm telescope N Billerica, MA
Nov 2	300mm telelens, Auvergne, France	Starmaster 14.5" Divide, CO
Nov 4	Hungary
Nov 5	8" SCT Santa Barbara,California
Nov 7	10" Schmidt-Newtonian Brevard County,Florida	10" Schmidt-Newtonian Alburgh,Vermont
Nov 10	Nikon 400 mm f/2.8 on CG-5, BW film Albuquerque, New Mexico
Nov 11	Bedford, New Hampshire
Nov 13	Marshall Twp, Pennsylvania
Nov 14	With Alpha Persei association, Canon 20d with 400mm f/2.8 telephoto on Meade LXD-55
Nov 15	Torquay, UK
Nov 18	Nikon 400 mm f/2.8 on CG-5 Elite Chrome 100 slide film West of Rio Rancho New Mexico
Nov 25	North Billerica MA, Astronight Observatory
Nov 29	Marshall Twp, Pennsylvania
Dec 14	Unprocessed single frame from Canon 5D / Canon 400 mm f/2.8 telephoto on Meade LXD-55
Dec 30	Unprocessed single frame from Canon 5D / Canon 400 mm f/2.8 telephoto on Meade LXD-55

[edit] Notes

^ ^a ^b Jewitt, David (09 Nov 2007). Comet Holmes Bigger Than The Sun. Institute for Astronomy at the University of Hawaii. Retrieved on 2007-11-17.
^ Editors. "Comet Holmes Stays Bright, Enlarges in the Evening Sky", Sky and Telescope, 27 October 2007. Retrieved 29 October 2007.
^ Davidson, J. E. "Comet e, 1889," The Observatory, July 1890, Vol. 13, pp. 247. Retrieved 27 October 2007.
^ Gunn, Angela. "Flash News Flash!," USA Today Tech Space, 24 October 2007. Retrieved 25 October 2007.
^ ^a ^b ^c Roger W. Sinnott (October 24, 2007). "Comet Holmes Undergoes Huge Outburst". Sky & Telescope.
^ ^a ^b ^c Fischer, Daniel. "Incredible comet eruption: from under 17th to 3rd magnitude in hours!," The Cosmic Mirror, #306, 24 October 2007. Retrieved 25 October 2007.
^ Skymap: late October 2007, Northeast, after sunset, Spaceweather.com. Retrieved 28 October 2007
^ Primary measurements, Chris L. Peterson 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.
^ Primary measurements, (see luminosity graph; bottom of page) Cloudbait Observatory, Colorado
^ 2 AU×(~150 Gm/AU)×sin(13 arcmin) ≈ 1.1 million km
^ Britt, Robert (15 Nov 2007). Incredible Comet Bigger than the Sun. Space.com. Retrieved on 2008-04-30.
^ "Comet Holmes brightens in retreat", BBC NEWS, 30 October 2007
^ Nasa 3D simulation of orbit for 17P/Holmes (Java Applet)
^ Cloudbait Observatory Gallery - Comet Holmes

[edit] External links

Wikimedia Commons has media related to:

17P/Holmes

17P at Kazuo Kinoshita's Comets
Quick Facts About Comet Holmes
17P at Seiichi Yoshida's Comet Catalog
Simple Instructions on How to Find Comet Holmes Instructions for the Amateur based around Toronto or New York.
Obscure Comet Brightens Suddenly
Evolution of Comet 17P/Holmes
Enigmatic Comet Holmes by Jeff Bryant, The Wolfram Demonstrations Project.

[edit] Photographs

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