View source for Astronomy:Comet Hale–Bopp

{{short description|Long-period comet}}
{{Infobox Comet
| name = C/1995 O1 (Hale–Bopp)
| image = Comet Hale-Bopp 1995O1.jpg
| caption = Comet Hale–Bopp, shortly after passing perihelion in April 1997
| pronounced = {{IPAc-en|,|h|ei|l|_|'|b|Q|p}}
| discoverer = {{ubl|[[Biography:Alan Hale (astronomer)|Alan Hale]]|[[Biography:Thomas Bopp|Thomas Bopp]]}}
| discovery_date = July 23, 1995
| designations = {{ubl||The Great Comet of 1997|C/1995 O1}}
| observation_arc = 29.2 years<ref name=jpldata/>
| orbit = Long period comet
| epoch = 2022-Sep-15<br />(JD 2459837.5)
| semimajor = 177 au
| perihelion = 0.914 au<ref name=jpl1996/>
| aphelion = 354 au<ref name=jpldata/>
| eccentricity = 0.99498
| period = (Barycentric 2399 yr)<ref name=barycenter>{{cite web |author=[[Astronomy:JPL Horizons On-Line Ephemeris System|Horizons]] output |url=https://ssd.jpl.nasa.gov/horizons_batch.cgi?batch=1&COMMAND=%27Hale-Bopp%27&TABLE_TYPE=%27ELEMENTS%27&START_TIME=%272022-Sep-15%27&STOP_TIME=%272022-Sep-16%27&STEP_SIZE=%27100%20years%27&CENTER=%27@0%27&OUT_UNITS=%27AU-D%27 |title=Barycentric Osculating Orbital Elements for Comet C/1995 O1 (Hale-Bopp) |access-date=2022-09-18}} (Solution using the Solar System [[Barycenter|barycenter]]. "PR = 8.763E+05 / 365.25 days" = 2399 years)</ref><br />{{nowrap|2364<ref name=jpldata/>–2520<ref name="NK1553">{{cite web |date=February 12, 2008 |title=OAA computing section circular NK 1553 |publisher=OAA Computing and Minor Planet Sections |author=Syuichi Nakano |url=http://www.oaa.gr.jp/~oaacs/nk/nk1553.htm |access-date=December 17, 2009}}</ref> [[Astronomy:Julian year|yr]]}}
| inclination = 89.3°
| dimensions = {{cvt|40–80|km}}<ref name=jpldata/>
| albedo = 0.01–0.07
| last_p = {{ubl|April 1, 1997<ref name=jpl1996>{{cite web |url = https://ssd.jpl.nasa.gov/sbdb.cgi?soln=J971A%2F1&sstr=Hale-Bopp&cad=1 |title = JPL SBDB Epoch 1996 |archive-url=https://web.archive.org/web/20210730214105/https://ssd.jpl.nasa.gov/sbdb.cgi?soln=J971A%2F1&sstr=Hale-Bopp&cad=1 |archive-date=30 July 2021 |url-status=dead}}</ref><ref name=MPEC1995-P01/>|2215 BC<ref name="Marsden1997"/>}}
| next_p = 4385 ± 2.0 AD<ref name=Hale-Bopp4385>{{cite web|title=Solex 10 estimate for Next Perihelion of C/1995 O1 (Hale-Bopp) |url=http://home.surewest.net/kheider/astro/Hale-Bopp4385.txt |access-date=December 18, 2009 |url-status=dead |archive-url=https://web.archive.org/web/20120810085857/http://home.surewest.net/kheider/astro/Hale-Bopp4385.txt |archive-date=August 10, 2012 }}</ref>
|mean_diameter={{cvt|60|km}}
|mean_radius={{cvt|30|km}}}}

'''Comet Hale–Bopp''' (formally designated '''C/1995&nbsp;O1''') is a [[Astronomy:Comet|comet]] that was one of the most widely observed of the 20th century and one of the brightest seen for many decades.

[[Biography:Alan Hale (astronomer)|Alan Hale]] and [[Biography:Thomas Bopp|Thomas Bopp]] discovered Comet Hale–Bopp separately on July 23, 1995, before it became visible to the [[Astronomy:Naked eye|naked eye]]. It is difficult to predict the maximum brightness of new comets with any degree of certainty, but Hale–Bopp exceeded most predictions when it passed perihelion on April 1, 1997, reaching about magnitude &minus;1.8. It was visible to the naked eye for a record 18&nbsp;months, due to its massive nucleus size.  This is twice as long as the [[Astronomy:Great Comet of 1811|Great Comet of 1811]], the previous record holder. Accordingly, Hale–Bopp was dubbed the [[Astronomy:Great comet|great comet]] of 1997.

== Discovery ==
The comet was discovered independently on July 23, 1995, by two observers, [[Biography:Alan Hale (astronomer)|Alan Hale]] and [[Biography:Thomas Bopp|Thomas Bopp]], both in the United States.<ref>{{cite journal |title = The comets of 1995 | last = Shanklin |first = Jonathan D. | journal = Journal of the British Astronomical Association | year= 2000 | volume =110 |issue = 6 |page= 311 |bibcode = 2000JBAA..110..311S}}</ref>

Hale had spent many hundreds of hours searching for comets without success, and was tracking known comets from his driveway in New Mexico when he chanced upon Hale–Bopp just after midnight. The comet had an [[Astronomy:Apparent magnitude|apparent magnitude]] of 10.5 and lay near the globular cluster M70 in the constellation of [[Astronomy:Sagittarius (constellation)|Sagittarius]].<ref name="Circ6187" /><ref name=Mobberley2013>{{citation | title=It Came From Outer Space Wearing an RAF Blazer!: A Fan's Biography of Sir Patrick Moore | first1=Martin | last1=Mobberley | publisher=Springer Science & Business Media | year=2013 | isbn=978-3319006093 | page=483 | url=https://books.google.com/books?id=dfO7BAAAQBAJ&pg=PA483 }}</ref> Hale first established that there was no other [[Astronomy:Deep-sky object|deep-sky object]] near M70, and then consulted a directory of known comets, finding that none were known to be in this area of the sky. Once he had established that the object was moving relative to the background stars, he emailed the [[Organization:Central Bureau for Astronomical Telegrams|Central Bureau for Astronomical Telegrams]], the clearing house for astronomical discoveries.<ref name="TimeDiscovery">{{cite magazine|title=Comet of the decade Part II| url = http://www.time.com/time/magazine/article/0,9171,986055,00.html | archive-url = https://web.archive.org/web/20081130085357/http://www.time.com/time/magazine/article/0,9171,986055,00.html | url-status = dead | archive-date = November 30, 2008 | magazine = Time | date=March 17, 1997 | first = Michael D. | last = Lemonick | access-date=October 30, 2008}}</ref>

Bopp did not own a [[Astronomy:Telescope|telescope]]. He was out with friends near Stanfield, Arizona, observing star clusters and [[Astronomy:Galaxy|galaxies]] when he chanced across the comet while at the eyepiece of his friend's telescope. He realized he might have spotted something new when, like Hale, he checked his star maps to determine if any other deep-sky objects were known to be near M70, and found that there were none. He alerted the Central Bureau for Astronomical Telegrams through a [[Company:Western Union|Western Union]] telegram. [[Biography:Brian G. Marsden|Brian G. Marsden]], who had run the bureau since 1968, laughed, "Nobody sends telegrams anymore. I mean, by the time that telegram got here, Alan Hale had already e-mailed us three times with updated coordinates."<ref name="NatGeo">{{cite web | url = http://science.nationalgeographic.com/science/space/solar-system/comets-age.html | title = The Age of Comets | first = William | date = December 1997 | last = Newcott | work = [[Organization:National Geographic Society|National Geographic Society]] | access-date = December 7, 2009 | archive-url = https://web.archive.org/web/20170829081936/http://science.nationalgeographic.com/science/space/solar-system/comets-age.html | archive-date = August 29, 2017 | url-status = dead | quote = Nobody sends telegrams anymore... }}</ref>

The following morning, it was confirmed that this was a new comet, and it was given the designation C/1995&nbsp;O1. The discovery was announced in [[Organization:International Astronomical Union|International Astronomical Union]] circular 6187.<ref name="Circ6187">{{cite web|last=Hale|first=A.|author2=Bopp, T.|author3=Stevens, J.|title=IAU Circular No. 6187|publisher=[[Organization:International Astronomical Union|IAU]] |date=July 23, 1995|url=http://www.cbat.eps.harvard.edu/iauc/06100/06187.html#Item1|access-date=July 5, 2011}}</ref><ref>{{cite journal | title = Amateur Contributions in the study of Comet Hale–Bopp | journal = Earth, Moon, and Planets | volume =79 | issue = 1–3 | year = 1997 | pages = 307–308 | first =Thomas | last =Bopp | s2cid = 117124838 | doi = 10.1023/A:1006262006364|bibcode = 1997EM&P...79..307B }}</ref>

== Early observation ==

Hale–Bopp's orbital position was calculated as 7.2&nbsp;astronomical units (au) from the Sun, placing it between [[Astronomy:Jupiter|Jupiter]] and [[Astronomy:Saturn|Saturn]] and by far the greatest distance from Earth at which a comet had been discovered by amateurs.<ref name=MPEC1995-P01>{{cite journal|title=Comet C/1995 O1 (Hale-Bopp) | url=http://www.minorplanetcenter.net/mpec/J95/J95P01.html | last=Marsden | first= B. G. |  year = 1995 | journal = Minor Planet Electronic Circular | volume=1995-P01}}</ref><ref>{{cite journal|title=Evolution of a Spiral Jet in the Inner Coma of Comet Hale-Bopp (1995 O1)| first1= M. R. | last1 =Kidger | doi=10.1086/310008 | journal = The Astrophysical Journal Letters | year=1996 | volume=461|issue=2| pages=L119–L122|last2=Serra-Ricart|first2=Miquel|last3=Bellot-Rubio|first3=Luis R.|last4=Casas|first4=Ricard | bibcode=1996ApJ...461L.119K| s2cid= 121572975 | doi-access=free}}</ref> Most comets at this distance are extremely faint, and show no discernible activity, but Hale–Bopp already had an observable [[Astronomy:Coma (cometary)|coma]].<ref name="Circ6187"/> A [[Astronomy:Precovery|precovery]] image taken at the [[Astronomy:UK Schmidt Telescope|UK Schmidt Telescope]] in 1993 was found to show the then-unnoticed comet some 13&nbsp;au from the Sun,<ref>{{cite web|last = McNaught| first = R. H. |author2=West, R. M.| title = Circular No. 6198| url=http://www.cbat.eps.harvard.edu/iauc/06100/06198.html|publisher=[[Organization:International Astronomical Union|IAU]] | date = August 2, 1995 |access-date=July 5, 2011}}</ref> a distance at which most comets are essentially unobservable. (Halley's Comet was more than 100 times fainter at the same distance from the Sun.)<ref>{{cite journal | last1=Biver | first1=N. | title = Substantial outgassing of CO from Comet Hale–Bopp at large heliocentric distance | journal = Nature | volume=380 | pages = 137–139 | year=1996 | doi=10.1038/380137a0 | pmid=8600385 | issue=6570 | last2=Rauer | first2=H | last3=Despois | first3=D | last4=Moreno | first4=R | last5=Paubert | first5=G | last6=Bockelée-Morvan | first6=D |author6-link=Dominique Bockelée-Morvan| last7=Colom | first7=P | last8=Crovisier | first8=J | last9=Gérard | first9=E| last10=Jorda | first10=Laurent | s2cid=4342525 |bibcode = 1996Natur.380..137B | display-authors=8 }}</ref> Analysis indicated later that its [[Astronomy:Comet nucleus|comet nucleus]] was 60±20&nbsp;kilometres in diameter, approximately six times the size of [[Astronomy:Halley's Comet|Halley's Comet]].<ref name=jpldata>{{cite web |type=2022-07-09 last obs |title=JPL Small-Body Database Browser: C/1995 O1 (Hale–Bopp) |url=https://ssd.jpl.nasa.gov/tools/sbdb_lookup.html#/?sstr=Hale-Bopp&view=OPC |access-date=2022-09-18}}</ref><ref name="Fernandez2002" />

Its great distance and surprising activity indicated that comet Hale–Bopp might become very bright when it reached perihelion in 1997. However, comet scientists were wary – comets can be extremely unpredictable, and many have large outbursts at great distance only to diminish in brightness later. [[Astronomy:Comet Kohoutek|Comet Kohoutek]] in 1973 had been touted as a 'comet of the century' and turned out to be unspectacular.<ref name="TimeDiscovery"/>

== Perihelion ==
[[File:Comet-Hale-Bopp-29-03-1997 hires adj.jpg|thumb|right|upright|The comet became a spectacular sight in early 1997.]]
[[File:Comet Hale-Bopp starmap 1997.png|thumb|Star map of path with 14-day motion marked]]
Hale–Bopp became visible to the [[Astronomy:Naked eye|naked eye]] in May 1996, and although its rate of brightening slowed considerably during the latter half of that year,<ref name="Kidger2004"/> scientists were still cautiously optimistic that it would become very bright. It was too closely aligned with the Sun to be observable during December 1996, but when it reappeared in January 1997 it was already bright enough to be seen by anyone who looked for it, even from large cities with [[Astronomy:Light pollution|light-polluted]] skies.<ref>{{cite news|title = Comet Holds Clues to Birth of Time | url = https://www.nytimes.com/1997/03/09/us/comet-holds-clues-to-birth-of-time.html?pagewanted=1 | last = Browne | first = Malcolm R. | date = March 9, 1997 | work = {{wipe|The New York Times}}}}</ref>

[[Internet|The Internet]] was a growing phenomenon at the time, and numerous websites that tracked the comet's progress and provided daily images from around the world became extremely popular. The Internet played a large role in encouraging the unprecedented public interest in comet Hale–Bopp.<ref>{{cite web| title= The Trail of Hale-Bopp | url= http://www.sciam.com/article.cfm?id=the-trail-of-hale-bopp | work= Scientific American | date= March 17, 1997 | access-date =October 23, 2008}}</ref>

As the comet approached the Sun, it continued to brighten, shining at 2nd&nbsp;magnitude in February, and showing a growing pair of [[Astronomy:Comet tail|tails]], the blue gas tail pointing straight away from the Sun and the yellowish dust tail curving away along its orbit. On March 9, a solar eclipse in China, Mongolia and eastern Siberia allowed observers there to see the comet in the daytime.<ref>{{cite journal |title = The total solar eclipse of 1997 March 9 | last1 = McGee | first1= H. W. | journal = Journal of the British Astronomical Association | year= 1997 | volume =107 |issue = 3 |pages= 112–113 |bibcode = 1997JBAA..107..112M| last2 = Poitevin | first2 = P. }}</ref> Hale–Bopp had its closest approach to Earth on March 22, 1997, at a distance of 1.315&nbsp;[[Astronomy:Astronomical unit|au]].<ref name="stardust">{{cite web |url=http://stardust.jpl.nasa.gov/science/hb.html |title=Comet Hale-Bopp |access-date=October 9, 2008 |work=Stardust|publisher=Jet Propulsion Laboratory, NASA |date= November 26, 2003}}</ref>

As it passed perihelion on April 1, 1997, the comet developed into a spectacular sight. It shone brighter than any star in the sky except [[Astronomy:Sirius|Sirius]], and its dust tail stretched 40–45 [[Degree (angle)|degrees]] across the sky.<ref>{{cite web|url=http://www.eso.org/public//events/astro-evt/hale-bopp/comet-hale-bopp-summary-apr13-97-rw.html |title=Comet Hale-Bopp (April 13, 1997) |access-date=November 23, 2008 |last=West |first=Richard M. |date=April 13, 1997 |publisher=European Southern Observatory |url-status=dead |archive-url=https://web.archive.org/web/20110524134423/http://www.eso.org/public/events/astro-evt/hale-bopp/comet-hale-bopp-summary-apr13-97-rw.html |archive-date=May 24, 2011 }}</ref><ref>{{cite journal | first=B. S. | last= Shylaja| journal=Bulletin of the Astronomical Society of India | volume=25 | pages=155–156 | year=1997 | title=What's New With Hale Bopp? | bibcode=1997BASI...25..155S}}</ref> The comet was visible well before the sky got fully dark each night, and while many great comets are very close to the Sun as they pass perihelion, comet Hale–Bopp was visible all night to Northern Hemisphere observers.<ref>{{cite web|url=http://www.eso.org/public//events/astro-evt/hale-bopp/comet-hale-bopp-summary-mar07-97-rw.html |title=Comet Hale-Bopp (March 7, 1997) |access-date=November 25, 2008 |last=West |first=Richard M. |author-link=Richard Martin West |date=March 7, 1997 |publisher=European Southern Observatory |url-status=dead |archive-url=https://web.archive.org/web/20110524135044/http://www.eso.org/public/events/astro-evt/hale-bopp/comet-hale-bopp-summary-mar07-97-rw.html |archive-date=May 24, 2011 }}</ref>

== After perihelion ==
After its perihelion passage, the comet moved into the [[Astronomy:Southern celestial hemisphere|southern celestial hemisphere]]. The comet was much less impressive to southern hemisphere observers than it had been in the northern hemisphere, but southerners were able to see the comet gradually fade from view during the second half of 1997. The last naked-eye observations were reported in December 1997, which meant that the comet had remained visible without aid for 569&nbsp;days, or about 18 and a half months.<ref name="Kidger2004">{{cite journal | last1 = Kidger| first1 = M.R. | year=2004 | journal = Earth, Moon, and Planets | volume = 78 | issue=1–3 | pages = 169–177 | title = The Visual Light Curve Of C/1995 O1 (Hale-Bopp) From Discovery To Late 1997 | doi=10.1023/A:1006228113533 | last2 = Hurst | first2 = G. | last3 = James | first3 = N.| s2cid = 120776226 |bibcode = 1997EM&P...78..169K }}</ref> The previous record had been set by the [[Astronomy:Great Comet of 1811|Great Comet of 1811]], which was visible to the naked eye for about 9 months.<ref name="Kidger2004"/>

The comet continued to fade as it receded, but was still tracked by astronomers. In October 2007, 10 years after the perihelion and at distance of 25.7 [[Astronomy:Astronomical unit|au]] from Sun, the comet was still active as indicated by the detection of the CO-driven coma.<ref>{{cite journal|last1=Szabó |first1= Gy. M.| journal=Astrophysical Journal Letters |year=2008|volume=677|issue=2|page=121 | title=Cometary Activity at 25.7 au: Hale-Bopp 11 Years after Perihelion|doi=10.1086/588095 | bibcode=2008ApJ...677L.121S|last2=Kiss|first2=L. L.|last3=Sárneczky|first3=K.|s2cid= 13344162|arxiv = 0803.1505 }}</ref> [[Astronomy:Herschel Space Observatory|Herschel Space Observatory]] images taken in 2010 suggest comet Hale–Bopp is covered in a fresh frost layer.<ref name="Szabó2012">{{cite journal |last=Szabó |first=Gy. M. |author2=Kiss, L. L.|author3=Kiss, Cs.|author4=Pál, A.|author5=Sárneczky, K.|author6=Juhász, A.|author7=Hogerheijde, M. R.|s2cid=119197339 |title=Evidence for fresh frost layer on the bare nucleus of comet Hale—Bopp at 32&nbsp;au distance |journal=Astrophysical Journal |volume= 761|issue= 1|page= 8|year=2012 |doi=  10.1088/0004-637X/761/1/8|arxiv=1210.2785 |bibcode= 2012ApJ...761....8S}}</ref> Hale–Bopp was again detected in December 2010 when it was 30.7&nbsp;au away from the Sun,<ref name="Szabó2011">{{cite journal |last=Szabó |first=M. |author2=Sárneczky, K. |author3=Kiss, L. L.  |s2cid=119113598 |title=Frozen to death? – Detection of comet Hale-Bopp at 30.7&nbsp;au |journal=Earth and Planetary Astrophysics |volume= 1104|page= 4351|year=2011 |doi= 10.1051/0004-6361/201116793|arxiv=1104.4351 |bibcode=  2011A&A...531A..11S}}</ref> and in 2012, at 33.2&nbsp;au from the Sun.<ref name="Herald2012">{{cite web
  |date=August 7, 2012
  |title=Comet Hale-Bopp C/1995 O1 - observed tonite
  |publisher=Yahoo Groups
  |author=Dave Herald
  |url=http://tech.groups.yahoo.com/group/comets-ml/message/19755
  |archive-url=https://archive.today/20130105121110/http://tech.groups.yahoo.com/group/comets-ml/message/19755
  |url-status=dead
  |archive-date=January 5, 2013
  |access-date=August 9, 2012}}</ref> The [[Astronomy:James Webb Space Telescope|James Webb Space Telescope]] observed Hale–Bopp in 2022, when it was 46.2&nbsp;au from the Sun.<ref name=MPEC2022-S20>[https://minorplanetcenter.net/mpec/K22/K22S20.html MPEC 2022-S20 : Observations and Orbits of Comets and A/ Objects] (2022 September 18)</ref>

== Orbital changes ==
[[File:Hale-Bopp orbit.svg|thumb|right|Hale–Bopp at perihelion on April 1, 1997]]
{{multiple image
| align = right
| direction = vertical
| width = 220
| header = Animation of Hale-Bopp orbit
| image1 = Animation of Hale-Bopp orbit.gif
| caption1 = Polar view
| image2 = Animation of Hale–Bopp orbit - equatorial view.gif
| caption2 = Equatorial view
| footer = {{legend2|magenta|  Hale–Bopp }}{{·}}{{legend2|Cyan|[[Astronomy:Mercury (planet)|Mercury]]}}{{·}}{{legend2| OrangeRed |[[Astronomy:Venus|Venus]] }}{{·}}{{legend2|Royalblue|Earth}} {{·}}{{legend2|Gold|[[Astronomy:Mars|Mars]] }}{{·}}{{legend2|Lime|[[Astronomy:Jupiter|Jupiter]] }} }}

The comet likely made its previous perihelion 4,200 years ago,<ref name=perturb>{{cite web
  |date=April 10, 1997
  |title=Comet Hale-Bopp Orbit and Ephemeris Information
  |publisher=JPL/NASA
  |author=Yeomans, Don
  |url=http://www2.jpl.nasa.gov/comet/ephemjpl8.html
  |access-date=October 23, 2008}}</ref> in July 2215&nbsp;BC.<ref name="Marsden1997"/> The estimated closest approach to Earth was 1.4&nbsp;au, and it may have been observed in ancient Egypt during the 6th dynasty reign of the Pharaoh Pepi II (Reign: 2247 – c. 2216 BC). Pepi's pyramid at Saqqara contains a text referring to an "nhh-star" as a companion of the pharaoh in the heavens, where "{{lang|egy|nhh}}" is the hieroglyph for long hair.<ref>"The Lost Tomb", Kent Weeks, {{ISBN|0-297-81847-3}}, page 198</ref>

Hale–Bopp may have had a near collision with Jupiter in early June 2215&nbsp;BC, which probably caused a dramatic change in its orbit, and 2215&nbsp;BC may have been its first passage through the inner Solar System from the [[Astronomy:Oort cloud|Oort cloud]].<ref name="Marsden1997"/> The comet's current orbit is almost [[Perpendicular|perpendicular]] to the plane of the [[Astronomy:Ecliptic|ecliptic]], so further close approaches to planets will be rare. However, in April 1996 the comet passed within 0.77&nbsp;au of [[Astronomy:Jupiter|Jupiter]], close enough for its orbit to be measurably affected by the planet's [[Physics:Gravity|gravity]].<ref name=perturb/> The comet's orbit was shortened considerably to a period of roughly 2,399&nbsp;years,<ref name=barycenter/> and it will next return to the inner [[Astronomy:Solar System|Solar System]] around the year 4385.<ref name=Hale-Bopp4385/> Its greatest distance from the Sun (aphelion) will be about 354&nbsp;au,<ref name=jpldata/> reduced from about 525&nbsp;au.<ref name=epoch1600>{{cite web |author=[[Astronomy:JPL Horizons On-Line Ephemeris System|Horizons]] output |url=https://ssd.jpl.nasa.gov/horizons_batch.cgi?batch=1&COMMAND=%27Hale-Bopp%27&TABLE_TYPE=%27ELEMENTS%27&START_TIME=%271600-01-01%27&STOP_TIME=%271600-01-02%27&STEP_SIZE=%27100%20years%27&CENTER=%27@0%27&OUT_UNITS=%27AU-D%27 |title=Barycentric Orbital Elements for Epoch 1600 |access-date=2022-09-19}} (Solution using the Solar System [[Barycenter|barycenter]]. "AD = 5.24E+02 and PR = 1.5536E+06 / 365.25 days" = 4254 years)</ref><ref name="Marsden1997">{{cite journal | title=Orbit Determination and Evolution of Comet C/1995 O1 (Hale-Bopp) | bibcode=1997EM&P...79....3M | last=Marsden | first=B. G. | s2cid=121368997 |  journal=Earth, Moon, and Planets | volume=79 | issue=1 | pages=3–15 | year=1997| doi=10.1023/A:1006268813208 }}</ref><ref name=cometfact>{{cite web |date=December 23, 2005 |title=Comet Fact Sheet |publisher=NASA (National Space Science Data Center) |author=Williams, David R. |url=http://nssdc.gsfc.nasa.gov/planetary/factsheet/cometfact.html |access-date=December 5, 2008}} (pre-[[Astronomy:Perturbation|perturbation]] orbit: semi-major axis 250&nbsp;au; period 4000yr)</ref>

The estimated probability of Hale-Bopp's striking Earth in future passages through the inner Solar System is remote, about 2.5×10<sup>−9</sup> per orbit.<ref name = "Weissman">{{Cite journal
 | last = Weissman | first = Paul R.
 | year = 2007
 | title = The cometary impactor flux at the Earth
 | journal = Proceedings of the International Astronomical Union
 | volume = 2 | issue = S236 | pages = 441–450
 | publisher = {{wipe|Cambridge University Press}}
 | doi = 10.1017/S1743921307003559
 | isbn=978-0-521-86345-2
| bibcode = 2007IAUS..236..441W
 | doi-access = free
 }}</ref> However, given that the comet nucleus is around 60&nbsp;km in diameter,<ref name=jpldata/> the consequences of such an impact would be apocalyptic. Weissman conservatively estimates the diameter at 35&nbsp;km; an estimated density of 0.6 g/cm<sup>3</sup> then gives a cometary mass of 1.3×10<sup>19</sup> g. At a probable impact velocity of 52.5&nbsp;km/s, impact energy can be calculated as 1.9×10<sup>32</sup> [[Physics:Erg|erg]]s, or 4.4×10<sup>9</sup> [[Physics:TNT equivalent|megatons]], about 44 times the estimated energy of the [[Biology:Alvarez hypothesis|K-T impact event]].<ref name = "Weissman" />

Over many orbits, the cumulative effect of gravitational perturbations on comets with high orbital inclinations and small perihelion distances is generally to reduce the perihelion distance to very small values. Hale–Bopp has about a 15%&nbsp;chance of eventually becoming a sungrazing comet through this process.<ref>{{cite journal | title=Orbit Determination and Evolution of Comet C/1995 O1 (Hale-Bopp) | bibcode=1996MNRAS.281..916B | last1=Bailey | first1=M. E. | journal=[[Organization:Monthly Notices of the Royal Astronomical Society|Monthly Notices of the Royal Astronomical Society]] | volume=281 | issue=1 | pages=916–924 | year=1996 | last2=Emel'Yanenko | first2=V. V. | last3=Hahn | first3=G. | last4=Harris | first4=N. W. | last5=Hughes | first5=K. A. | last6=Muinonen | first6=K. | last7=Scotti | first7=J. V. | doi=10.1093/mnras/281.3.916| citeseerx=10.1.1.29.6010 }}</ref>  If such is the case, it could undergo huge mass loss, or break up into smaller pieces like the Kreutz sungrazers.  It would also be extremely bright, due to a combination of closeness to the Sun and nuclei size, potentially exceeding Halley’s Comet in 837 AD.

== Scientific results ==
Due to the massive size of its nucleus, Comet Hale–Bopp was observed intensively by [[Astronomy:Astronomer|astronomer]]s during its perihelion passage, and several important advances in cometary science resulted from these observations. The dust production rate of the comet was very high (up to 2.0{{e|6}} kg/s),<ref name="Jewitt1999">{{cite journal | title= Particulate Mass Loss from Comet Hale-Bopp | bibcode = 1999AJ....117.1056J | journal = The Astronomical Journal | volume = 117 | issue = 2 | pages = 1056–1062 | last1=Jewitt | first1 = David | year=1999 | doi=10.1086/300743 | last2= Matthews | first2= Henry| s2cid = 120740179 | doi-access = free }}</ref> which may have made the inner coma optically thick.<ref>{{cite journal | last1 = Fernández | first1= Yanga R. | title = The Inner Coma and Nucleus of Comet Hale–Bopp: Results from a Stellar Occultation | bibcode = 1999Icar..140..205F | year = 1999 | journal = Icarus | volume = 140 | issue = 1 | pages = 205–220 | doi = 10.1006/icar.1999.6127| last2= Wellnitz | first2= Dennis D. | last3= Buie | first3= Marc W. | last4= Dunham | first4= Edward W. | last5= Millis | first5= Robert L. | last6= Nye | first6= Ralph A. | last7= Stansberry | first7= John A. | last8= Wasserman | first8= Lawrence H. | last9= a'Hearn | first9= Michael F. | last10= Lisse | first10= Carey M. | last11= Golden | first11= Meg E. | last12= Person | first12= Michael J. | last13= Howell | first13= Robert R. | last14= Marcialis | first14= Robert L. | last15= Spitale | first15= Joseph N. | s2cid= 43229796 }}</ref> Based on the properties of the dust grains—high temperature, high [[Earth:Albedo|albedo]] and strong 10&nbsp;μm silicate emission feature—the astronomers concluded the dust grains are smaller than observed in any other comet.<ref>{{cite journal | title = Observations of Unusually Small Dust Grains in the Coma of Comet Hale-Bopp C/1995 O1 | bibcode = 2001ApJ...549..635M | last1 = Mason | first1=C. G. | journal = The Astrophysical Journal | year=2001 | volume = 549 | issue = 1 | pages = 635–646 | doi = 10.1086/319039 | last2 = Gehrz | first2 = R. D. | last3 = Jones | first3 = T. J. | last4 = Woodward | first4 = C E. | last5 = Hanner | first5 = M. S. | last6 = Williams | first6 = D. M.| doi-access = free }}</ref>

Hale–Bopp showed the highest ever linear polarization detected for any comet. Such polarization is the result of solar radiation getting scattered by the dust particles in the coma of the comet and depends on the nature of the grains. It further confirms that the dust grains in the coma of comet Hale–Bopp were smaller than inferred in any other comet.<ref>{{cite journal | title = Polarimetric observations of the comet Hale-Bopp | bibcode = 1998A&AS..129..489G | last1 = Ganesh | first1=S. | journal = Astronomy and Astrophysics Supplement | year=1998 | volume = 129 | issue = 5 | pages = 489–493 | doi = 10.1051/aas:1998201 | last2 = Joshi | first2 = U. C. | last3 = Baliyan | first3 = K. S. | last4 = Deshpande | first4 = M. R.| doi-access = free }}</ref>

=== Sodium tail ===
[[File:Hale-Bopp sodium tail.gif|thumb|right|Comet Hale–Bopp's neutral sodium tail (the straight tail extending up to the left from the nucleus)<ref name="Cremonese1997" />]]
One of the most remarkable discoveries was that the comet had a third type of tail. In addition to the well-known gas and dust tails, Hale–Bopp also exhibited a faint [[Chemistry:Sodium|sodium]] tail, only visible with powerful instruments with dedicated filters. Sodium emission had been previously observed in other comets, but had not been shown to come from a tail. Hale–Bopp's sodium tail consisted of [[Physics:Electric charge|neutral atoms]] (not [[Physics:Ion|ion]]s), and extended to some 50&nbsp;million kilometres in length.<ref name="Cremonese1997">{{cite journal | journal = The Astrophysical Journal Letters | volume = 490 | issue = 2 | pages =L199–L202 | year = 1997 | doi =  10.1086/311040 | title = Neutral Sodium from Comet Hale–Bopp: A Third Type of Tail | author1 = Cremonese, G | author2 = Boehnhardt, H | author3 = Crovisier, J | author4 = Rauer, H | author5 = Fitzsimmons, A | author6 = Fulle, M | author7 = Licandro, J | author8 = Pollacco, D | author9 = Tozzi, G P | bibcode=1997ApJ...490L.199C|arxiv = astro-ph/9710022 | display-authors = 8 | last10 = West | first10 = R. M. | s2cid = 119405749 }}</ref>

The source of the sodium appeared to be the inner [[Astronomy:Coma (cometary)|coma]], although not necessarily the [[Astronomy:Comet nucleus|nucleus]]. There are several possible mechanisms for generating a source of sodium atoms, including collisions between dust grains surrounding the nucleus, and "sputtering" of sodium from dust grains by [[Physics:Ultraviolet|ultraviolet]] light. It is not yet established which mechanism is primarily responsible for creating Hale–Bopp's sodium tail, and the narrow<ref name="Cremonese1997" /> and diffuse<ref>{{cite journal | last1=Wilson |first1=J. K.| title=Three tails of comet Hale-Bopp | bibcode = 1998GeoRL..25..225W | journal=Geophysical Research Letters | volume=25 | issue=3 | pages=225–228 | doi=10.1029/97GL03704 | year=1998 | last2=Baumgardner | first2=J. | last3=Mendillo | first3=M.|s2cid=129323918 | doi-access=free }}</ref> components of the tail may have different origins.<ref>{{cite journal | first1=G. | last1=Cremonese | title=Sodium In Comets | bibcode=1997EM&P...79..209C | journal=Earth, Moon, and Planets | volume=79 | issue=1 | pages=209–220 | year=1997 | doi=10.1023/A:1006245619568 | last2=Fulle | first2=Marco| s2cid=118693620 }}</ref>

While the comet's dust tail roughly followed the path of the comet's orbit and the gas tail pointed almost directly away from the Sun, the sodium tail appeared to lie between the two. This implies that the sodium atoms are driven away from the comet's head by [[Astronomy:Radiation pressure|radiation pressure]].<ref name="Cremonese1997" />

=== Deuterium abundance ===
The abundance of [[Physics:Deuterium|deuterium]] in comet Hale–Bopp in the form of [[Chemistry:Heavy water|heavy water]] was found to be about twice that of Earth's oceans. If Hale–Bopp's deuterium abundance is typical of all comets, this implies that although cometary impacts are thought to be the source of a significant amount of the [[Earth:Origin of water on Earth|water on Earth]], they cannot be the only source.<ref name="Cometwater">{{cite journal | title = Cometary Deuterium | journal = Space Science Reviews | volume = 90 | issue = 1–2 | year = 1999 | doi = 10.1023/A:1005269208310 | pages = 33–43 | first1 = Roland | last1 = Meier | last2 = Owen | first2 = Tobias C.| s2cid = 34317575 | pmid = 11543290 |bibcode = 1999SSRv...90...33M }}</ref>

Deuterium was also detected in many other [[Chemistry:Hydrogen|hydrogen]] compounds in the comet. The ratio of deuterium to normal hydrogen was found to vary from compound to compound, which astronomers believe suggests that cometary ices were formed in [[Astronomy:Interstellar cloud|interstellar cloud]]s, rather than in the solar nebula. Theoretical modelling of ice formation in interstellar clouds suggests that comet Hale–Bopp formed at temperatures of around 25–45&nbsp;[[Kelvin|kelvin]]s.<ref name="Cometwater"/>

=== Organics ===
Spectroscopic observations of Hale–Bopp revealed the presence of many [[Chemistry:Organic chemistry|organic chemicals]], several of which had never been detected in comets before. These complex molecules may exist within the cometary nucleus, or might be synthesised by reactions in the comet.<ref name="Cometorganic">{{cite journal | title = Organic synthesis in the coma of Comet Hale–Bopp?| journal = Monthly Notices of the Royal Astronomical Society| volume = 320 | issue = 4 | year = 2002| doi = 10.1046/j.1365-8711.2001.04208.x | pages = L61–L64  | first1 = S. D. | last1 = Rodgers | last2 = Charnley | first2 = S. B.|bibcode = 2001MNRAS.320L..61R | doi-access = free }}</ref>

=== Detection of argon ===
Hale–Bopp was the first comet where the [[Chemistry:Noble gas|noble gas]] [[Chemistry:Argon|argon]] was detected.<ref name="Argon" /> Noble gases are chemically inert and vary from low to high [[Chemistry:Volatility|volatility]]. Since different noble elements have different [[Sublimation (phase transition)|sublimation]] temperatures, and don't interact with other elements, they can be used for probing the temperature histories of the cometary ices. [[Chemistry:Krypton|Krypton]] has a sublimation temperature of 16–20&nbsp;K and was found to be depleted more than 25 times relative to the solar abundance,<ref>{{cite journal | title=Detection of Soft X-rays and a Sensitive Search for Noble Gases in Comet Hale-Bopp (C/1995 O1) | bibcode=1997Sci...277.1488K | last1=Krasnopolsky | first1=Vladimir A. | year = 1997 | journal=Science | volume=277 | pages=1488–1491 | doi=10.1126/science.277.5331.1488 | pmid=9278508 | issue=5331 | last2=Mumma | first2=MJ | last3=Abbott | first3=M | last4=Flynn | first4=BC | last5=Meech | first5=KJ | last6=Yeomans | first6=DK | last7=Feldman | first7=PD | last8=Cosmovici | first8=CB| url=https://zenodo.org/record/1231120 }}</ref> while argon with its higher sublimation temperature was enriched relative to the solar abundance.<ref name="Argon">{{cite journal | title=The Discovery of Argon in Comet C/1995 O1 (Hale-Bopp) | bibcode=2000ApJ...544L.169S | last1=Stern | first1=S. A. | year=2000 | journal=The Astrophysical Journal | volume=544 | issue=2 | pages = L169–L172 | doi=10.1086/317312 | last2=Slater | first2=D. C. | last3=Festou | first3=M. C. | last4=Parker | first4=J. Wm. | last5=Gladstone | first5=G. R. | last6=A'hearn | first6=M. F. | last7=Wilkinson | first7=E.| s2cid=16759616 |arxiv = astro-ph/0011327 }}</ref> Together these observations indicate that the interior of Hale–Bopp has always been colder than 35–40&nbsp;K, but has at some point been warmer than 20&nbsp;K. Unless the solar nebula was much colder and richer in argon than generally believed, this suggests that the comet formed beyond Neptune in the [[Astronomy:Kuiper belt|Kuiper belt]] region and then migrated outward to the [[Astronomy:Oort cloud|Oort cloud]].<ref name="Argon" />

=== Rotation ===
Comet Hale–Bopp's activity and outgassing were not spread uniformly over its nucleus, but instead came from several specific jets. Observations of the material streaming away from these jets<ref>{{cite web |url=http://www2.jpl.nasa.gov/comet/anim30.html |title=Bergeron Comet Hale-Bopp Animation |access-date=October 14, 2008 |work=Stardust|publisher=Jet Propulsion Laboratory, NASA}}</ref> allowed astronomers to measure the rotation period of the comet, which was found to be about 11 hours 46 minutes.<ref>{{cite journal | journal = Astronomy and Astrophysics Supplement Series |volume = 136 | issue = 2 |pages =245–256 | year = 1999 | doi = 10.1051/aas:1999213 | title = Dust continuum imaging of C/1995 O1 (Hale-Bopp): Rotation period and dust outflow velocity | author1 = Warell, J. | author2 = Lagerkvist, C.-I. | author3 = Lagerros, J. S. V.|bibcode = 1999A&AS..136..245W | doi-access = free }}</ref>

=== Binary nucleus question ===
In 1997 a paper was published that hypothesised the existence of a binary [[Astronomy:Comet nucleus|nucleus]] to fully explain the observed pattern of comet Hale–Bopp's dust emission observed in October 1995. The paper was based on theoretical analysis, and did not claim an observational detection of the proposed satellite nucleus, but estimated that it would have a diameter of about 30&nbsp;km, with the main nucleus being about 70&nbsp;km across, and would orbit in about three days at a distance of about 180&nbsp;km.<ref>{{cite journal | title = Detection of a Satellite Orbiting The Nucleus of Comet Hale–Bopp (C/1995 O1) | journal = Earth, Moon, and Planets | volume = 77 | issue = 3 | year = 1997 | doi = 10.1023/A:1006230712665 | pages = 155–163 | first = Z. | last = Sekanina| s2cid = 122481110 |bibcode = 1997EM&P...77..155S }}</ref> This analysis was confirmed by observations in 1996 using Wide-Field Planetary Camera 2 of the [[Astronomy:Hubble Space Telescope|Hubble Space Telescope]] which had taken images of the comet that revealed the satellite.<ref>{{cite journal
| title=Detection of a Satellite orbiting the Nucleus of Comet Hale-Bopp (C/1995 O1)
| journal = Earth, Moon, and Planets
| volume = 77
| issue = 3
| pages = 155–163
| last=Sekanina
| first=Z.
| date = 1997
| s2cid = 122481110
| publisher=European Organisation for Astronomical Research in the Southern Hemisphere
| bibcode = 1997EM&P...77..155S
| doi = 10.1023/A:1006230712665
}}</ref>

Although observations using [[Astronomy:Adaptive optics|adaptive optics]] in late 1997 and early 1998 showed a double peak in the brightness of the nucleus,<ref>{{cite journal | last1 = Marchis | first1 = F. | journal = Astronomy & Astrophysics | year = 1999 | title = Adaptive optics observations of the innermost coma of C/1995 O1. Are there a "Hale" and a "Bopp" in comet Hale-Bopp? | url = http://aa.springer.de/papers/9349003/2300985.pdf | volume = 349 | pages = 985–995 | bibcode = 1999A&A...349..985M | last2 = Boehnhardt | first2 = H. | last3 = Hainaut | first3 = O. R. | last4 = Le Mignant | first4 = D. | access-date = October 29, 2008 | archive-url = https://web.archive.org/web/20081031064051/http://aa.springer.de/papers/9349003/2300985.pdf | archive-date = October 31, 2008 | url-status = dead }}</ref> controversy still exists over whether such observations can only be explained by a binary nucleus.<ref name="Fernandez2002" /> The discovery of the satellite was not confirmed by other observations.<ref>{{cite journal| last1=McCarthy | first1=D. W. | title=Comet Hale–Bopp in outburst: Imaging the dynamics of icy particles with HST/NICMOS | bibcode=2007Icar..189..184M | year=2007 | journal=Icarus | volume = 189 | issue = 1 | pages = 184–195| doi=10.1016/j.icarus.2007.01.019| last2=Stolovy| first2=S| last3=Campins| first3=H| last4=Larson| first4=S| last5=Samarasinha| first5=N| last6=Kern| first6=S}}</ref><ref>{{cite journal | last1=Weaver | first1=H. A.| title = Post-Perihelion HST Observations of Comet Hale–Bopp (C/1995 O1) | bibcode=1999Icar..141....1W | year=1999 | journal=Icarus | volume=141 | issue =1 | doi=10.1006/icar.1999.6159 | pages=1–12| last2=Feldman| first2=P. D.| last3=a'Hearn| first3=M. F.| last4=Arpigny| first4=C.| last5=Brandt| first5=J. C.| last6=Stern| first6=S. A.| doi-access=free}}</ref> Also, while comets have been observed to break up before,<ref>{{cite journal | last=Sekanina | first = Z. | title = The problem of split comets revisited | bibcode = 1997A&A...318L...5S | journal = Astronomy and Astrophysics Letters | year = 1997 | volume = 318 | pages = L5–L8 }}</ref> no case had been found of a stable binary nucleus until the subsequent discovery of {{mp|P/2006 VW|139}}.

== UFO claims ==
{{main|Philosophy:Heaven's Gate (religious group)}}
In November 1996, amateur astronomer Chuck Shramek of Houston, Texas took a [[Engineering:Charge-coupled device|CCD]] image of the comet which showed a fuzzy, slightly elongated object nearby. His computer sky-viewing program did not identify the star, so Shramek called the [[Biography:Art Bell|Art Bell]] radio program ''[[Unsolved:Coast to Coast AM|Coast to Coast AM]]'' to announce that he had discovered a "Saturn-like object" following Hale–Bopp. UFO enthusiasts, such as [[Unsolved:Remote viewing|remote viewing]] proponent and [[Organization:Emory University|Emory University]] political science professor [[Biography:Courtney Brown (researcher)|Courtney Brown]], soon concluded that there was an alien spacecraft following the comet.<ref name="time">{{cite magazine|title=The man who spread the myth | url = http://www.time.com/time/magazine/article/0,9171,986171,00.html | archive-url = https://web.archive.org/web/20051121060305/http://www.time.com/time/magazine/article/0,9171,986171,00.html | url-status = dead | archive-date = November 21, 2005 | magazine=Time| date=April 14, 1997 | first = Leon | last = Jaroff |author2=Willwerth, James | access-date=October 30, 2008}}</ref>

Several astronomers, including Alan Hale, stated that the object was simply the 8.5-magnitude star SAO141894.<ref>{{cite journal | title = Hale-Bopp Comet Madness | first = Alan | last = Hale | journal = Skeptical Inquirer | year = 1997 | volume = 21 | issue = 2 | pages = 25–28 | url = http://www.csicop.org/si/show/hale-bopp_comet_madness/ | access-date = December 6, 2009 | archive-url = https://web.archive.org/web/20100208233213/http://www.csicop.org/si/show/hale-bopp_comet_madness | archive-date = February 8, 2010 | url-status = dead }}</ref> They noted that the star did not appear on Shramek's computer program because the user preferences were set incorrectly.<ref>{{cite book|title=Great Comets|first=Robert|last=Burnham|author2=Levy, David H.|year=2000|publisher=Cambridge University Press|isbn=978-0-521-64600-0|page=[https://archive.org/details/greatcomets00burn/page/191 191]|url-access=registration|url=https://archive.org/details/greatcomets00burn/page/191}}</ref> Art Bell claimed to have obtained an image of the object from an anonymous astrophysicist who was about to confirm its discovery. However, astronomers Olivier Hainaut and [[Biography:David J. Tholen|David Tholen]] of the [[Organization:University of Hawaii|University of Hawaii]] stated that the alleged photo was an altered copy of one of their own comet images.<ref>{{cite web  |date=January 15, 1997 | title=Fraudulent use of an IfA/UH picture |url=http://www.sc.eso.org/~ohainaut/Hale_Bopp/hb_ufo_tholen.html | publisher=European Organisation for Astronomical Research in the Southern Hemisphere |access-date=October 14, 2008|  first = David J. | last = Tholen |archive-url = https://web.archive.org/web/20070930225155/http://www.sc.eso.org/~ohainaut/Hale_Bopp/hb_ufo_tholen.html |archive-date = September 30, 2007}}</ref>

Thirty-nine members of the [[Philosophy:Heaven's Gate (religious group)|Heaven's Gate]] cult committed mass suicide in March 1997 with the intention of teleporting to a spaceship which they believed was flying behind the comet.<ref>{{cite journal | title = Heaven's Gate: The End | first = Wendy Gale | last = Robinson | journal = Journal of Computer-Mediated Communication | volume = 3 | issue = 3 | url = http://jcmc.indiana.edu/vol3/issue3/robinson.html | doi=10.1111/j.1083-6101.1997.tb00077.x| year = 2006 }}</ref>

Nancy Lieder, who claims to receive messages from aliens through an implant in her brain, stated that Hale–Bopp was a fiction designed to distract the population from the coming arrival of [[Unsolved:Nibiru cataclysm|"Nibiru"]] or "Planet X", a giant planet whose close passage would disrupt the Earth's rotation, causing global cataclysm.<ref>{{cite news|title= Comets Breed Fear, Fascination and Web Sites|author=George Johnson|url=https://www.nytimes.com/1997/03/28/us/comets-breed-fear-fascination-and-web-sites.html?sec=health&spon=&pagewanted=all|access-date=September 27, 2009 | work=The New York Times | date=March 28, 1997}}</ref> Her original date for the apocalypse was May 2003, which passed without incident, but various conspiracy websites continued to predict the coming of Nibiru, most of whom tied it to the [[Social:2012 phenomenon|2012 phenomenon]].<ref name=myth>{{cite web|title=The Myth of Nibiru and the End of the World in 2012|author=David Morrison|publisher=Skeptical Inquirer|url=http://www.csicop.org/si/2008-05/morrison.html|access-date=April 28, 2009|archive-url=https://web.archive.org/web/20090421022039/http://www.csicop.org/si/2008-05/morrison.html|archive-date=April 21, 2009|url-status=dead}}</ref> Lieder and others' claims of the planet Nibiru have been repeatedly debunked by scientists.<ref>{{cite web |url=https://www.space.com/15551-nibiru.html |title=Nibiru: The Nonexistent Planet |website=Space.com |date=December 4, 2018 |access-date=July 17, 2020}}</ref>

== Legacy ==
[[File:ESO-Comet Hale-Bopp-Phot-07a-01-hires.jpg|thumb|right| Comet Hale–Bopp in 2001, at a distance of nearly two billion kilometres from the Sun. Credit: ESO]]Its lengthy period of visibility and extensive coverage in the media meant that Hale–Bopp was probably the most-observed comet in history, making a far greater impact on the general public than the return of Halley's Comet in 1986, and certainly seen by a greater number of people than witnessed any of Halley's previous appearances. For instance, 69% of Americans had seen Hale–Bopp by April 9, 1997.<ref name="Aguirre">{{cite journal | last = Aguirre | first = Edwin L. | title = The Great Comet of 1997 | journal = Sky and Telescope | url = https://pqasb.pqarchiver.com/skyandtelescope/access/886291661.html?dids=886291661:886291661&FMT=CITE&FMTS=CITE:PAGE&date=Jul+1997&author=Edwin+L+Aguirre&desc=The+Great+Comet+of+1997 | date = July 1997 | access-date = July 5, 2017 | archive-date = January 16, 2009 | archive-url = https://web.archive.org/web/20090116131943/http://pqasb.pqarchiver.com/skyandtelescope/access/886291661.html?dids=886291661:886291661&FMT=CITE&FMTS=CITE:PAGE&date=Jul+1997&author=Edwin+L+Aguirre&desc=The+Great+Comet+of+1997 | url-status = dead }}</ref>

Hale–Bopp was a record-breaking comet—the farthest comet from the Sun discovered by amateurs,<ref name="stardust" /> with the largest well-measured cometary nucleus known after 95P/Chiron,<ref name="Fernandez2002">{{cite journal | last = Fernández | first=Yanga R. | s2cid=189899565 | title = The Nucleus of Comet Hale-Bopp (C/1995 O1): Size and Activity | year = 2002 | journal = Earth, Moon, and Planets | volume = 89 | issue=1 | pages = 3–25| doi = 10.1023/A:1021545031431|bibcode = 2002EM&P...89....3F }}</ref> and it was visible to the naked eye for twice as long as the previous record-holder.<ref name="Kidger2004"/> It was also brighter than magnitude&nbsp;0 for eight&nbsp;weeks, longer than any other recorded comet.<ref name="stardust"/>

[[Biography:Carolyn S. Shoemaker|Carolyn Shoemaker]] and her husband [[Biography:Eugene Merle Shoemaker|Gene]], both famous for co-discovering [[Astronomy:Comet Shoemaker–Levy 9|comet Shoemaker–Levy 9]], were involved in a car crash after photographing the comet. Gene died in the crash and his ashes were sent to the Moon aboard NASA's ''[[Astronomy:Lunar Prospector|Lunar Prospector]]'' mission along with an image of Hale–Bopp, "the last comet that the Shoemakers observed together".<ref>{{cite web|url=http://www2.jpl.nasa.gov/sl9/news82.html|title=Eugene Shoemaker Ashes Carried on Lunar Prospector|website=www2.jpl.nasa.gov}}</ref>

== See also ==
* [[Astronomy:Comet Hyakutake|Comet Hyakutake]]
* ''Hale Bopp'' (Waterhouse), a 1997 string orchestra composition 
* [[Astronomy:Lists of comets|Lists of comets]]
{{clear}}

== References ==
{{Reflist}}

== External links ==
* [http://cometbase.net/en/observation/listObserv/478 CometBase: Comet Hale-Bopp]
* [http://www.cometography.com/lcomets/1995o1.html Cometography.com: Comet Hale-Bopp]
* [http://www.jpl.nasa.gov/comet NASA Hale-Bopp page]
* [https://web.archive.org/web/20110827030726/http://shadowandsubstance.com/Past%20graphics/Comet%20Hale-Bopp%20orbit.htm Shadow and Substance.com: Static orbital diagram]
* [https://web.archive.org/web/20070929083554/http://one.revver.com/watch/90657/flv/affiliate/14715 Comet Nucleus Animation]
* {{cite journal |arxiv=1404.2562|doi=10.1016/j.icarus.2014.03.033|bibcode=2014Icar..236..136K|title=A dynamical analysis of the dust tail of Comet C/1995 O1 (Hale–Bopp) at high heliocentric distances|year=2014|last1=Kramer|first1=Emily A.|last2=Fernandez|first2=Yanga R.|last3=Lisse|first3=Carey M.|last4=Kelley|first4=Michael S.P.|last5=Woodney|first5=Laura M.|s2cid=119201510|journal=Icarus|volume=236|pages=136–145}}
* {{JPL Small Body|name=Hale-Bopp}}


{{DEFAULTSORT:Hale-Bopp, 1995 O1}}
[[Category:Non-periodic comets]]
[[Category:Great comets]]

{{Sourceattribution|Comet Hale–Bopp}}