Anti-tail

{{Short description|Feature of a comet}}

File:C2007N3Lulin2panel brimacombe.jpg antitail to the left, ion tail to right]]

File:Comet A3 2023 Tsuchinshan-Atlas.jpg as it appeared on October 14th 2024 with a prominent "anti-tail" pointing towards the horizon.]]

File:Anti-tail.jpg

An antitail, also known as an anti-tail, is an apparent spike projecting from a comet's coma which seems to go towards the Sun, and thus geometrically opposite to the other tails: the ion tail and the dust tail. Despite a common misunderstanding, this phenomenon is not an optical illusion. The antitail consists of larger dust particles left behind by the comet. These dust particles are less affected by the Sun's radiation pressure and tend to remain roughly in the comet's orbital plane and eventually form a disc along the comet's orbit due to the ejection speed of the particles from the comet's surface. As Earth passes through the comet's orbital plane, this disc is seen side on, and appears as the characteristic spike.{{cite journal |last1=Boehnhardt |first1=Hermann |title=The Anti-Tail of Comet C/1995 O1 (Hale–Bopp) in 1997/1998 |journal=Earth, Moon, and Planets |date=2003 |volume=93 |issue=1 |pages=19-35 |url=https://link.springer.com/content/pdf/10.1023/B:MOON.0000034496.28985.ef.pdf |access-date=17 October 2024}}

The other side of the disc can sometimes be seen, though it tends to be lost in the dust tail. The antitail is therefore normally visible for a brief interval only when Earth passes through the comet's orbital plane.{{cite web|url=http://www.space.com/spacewatch/090206-ns-comet-lulin.html|title=Newfound Comet Lulin to Grace Night Skies |last=Rao|first= Joe |date=6 February 2009|publisher=SPACE.com|access-date=2009-02-25| archive-url= https://web.archive.org/web/20090226001704/http://www.space.com/spacewatch/090206-ns-comet-lulin.html| archive-date= 26 February 2009 | url-status= live}}{{cite web|url=http://3.bp.blogspot.com/_yM063m-CN3M/SZ9YzVzA0OI/AAAAAAAAANk/627phmwTv14/s1600-h/antitail.jpg|title=What is an antitail|last=Tosar|first=Borja|author2=Paolo Candy|work=3.bp.blogspot|access-date=2009-02-25| archive-url= https://web.archive.org/web/20090225130604/http://3.bp.blogspot.com/_yM063m-CN3M/SZ9YzVzA0OI/AAAAAAAAANk/627phmwTv14/s1600-h/antitail.jpg| archive-date= 25 February 2009 | url-status= live}}

Most comets do not develop sufficiently for an antitail to become visible, but notable comets that did display antitails include Comet Arend–Roland in 1957,{{cite web|title=Encyclopedia of science:antitail|url=http://www.daviddarling.info/encyclopedia/A/antitail.html| author=David Darling| date=2016}} Comet Kohoutek in 1973,{{cite journal |title=Statement of John E. Naugle, Associate Administrator for Space Science, NASA: Comet Kohoutek Program |journal=Hearings Before the Subcommittee on Space Science and Applications |first1=John E. |last1=Naugles |volume=25 |issue=3 |pages=401 |date=7 March 1974 |location=Washington DC |department=Committee on Science and Astronautics U.S. House of Representatives |url=https://books.google.com/books?id=QVAVAAAAIAAJ&pg=PA401 |access-date=2021-11-10 |quote=[drawing on page 403] the Skylab crewmen observed a brilliant spike or anti tail projecting toward the Sun from the head of Kohoutek [...] Dr Zdenek Sekanina concluded that the spike was not wholly due to a perspective or geometrical effect as has been assumed in previous comet studies.}} Comet Hale–Bopp in 1997, C/1999 H1 (Lee){{cite web|url=https://fg-kometen.vdsastro.de/koj_1999/c1999h1/99h1eaus.htm|title=Analysis of past comet apparitions – C/1999 H1 (Lee)|last=Kammerer|first=Andreas|access-date=2023-11-24}} in 1999, Comet Lulin in 2009, Comet PANSTARRS in 2013, C/2022 E3 (ZTF) in 2023,{{Cite web |author1=Harry Baker |date=2023-01-27 |title=Optical illusion gives rare green comet an 'anti-tail' that seemingly defies physics |url=https://www.space.com/green-comet-anti-tail-illusion |access-date=2023-01-28 |website=Space.com |language=en}} 12P/Pons–Brooks{{Cite web |author=Adrien |date=2024-06-15 |url=https://www.techno-science.net/en/news/the-devil-comet-reveals-an-anti-tail-N25126.html |title="The Devil's Comet reveals... an anti-tail" |access-date=2024-10-15 |website=techno-science.net |language=en}} in 2024 and C/2023 A3 Tsuchinshan–ATLAS{{Cite web |author1=Bob King |date=2024-10-15 |url=https://skyandtelescope.org/astronomy-news/comet-tsuchinshan-atlas-climbs-brightens-and-delights/ |title="Comet Tsuchinshan-ATLAS climbs, brigthens and delights!" |access-date=2024-10-15 |website=SkyAndTelescope.org |language=en |quote="The comet displayed a strikingly narrow antitail the night of October 14th"}}

in 2024.