An antitail, also known as an anti-tail, is an apparent spike projecting from a

comet A comet is an icy, small Solar System body that warms and begins to release gases when passing close to the Sun, a process called outgassing. This produces an extended, gravitationally unbound atmosphere or Coma (cometary), coma surrounding ...

coma A coma is a deep state of prolonged unconsciousness in which a person cannot be awakened, fails to Nociception, respond normally to Pain, painful stimuli, light, or sound, lacks a normal Circadian rhythm, sleep-wake cycle and does not initiate ...

which seems to go towards the

Sun The Sun is the star at the centre of the Solar System. It is a massive, nearly perfect sphere of hot plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy from its surface mainly as visible light a ...

, 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 In visual perception, an optical illusion (also called a visual illusion) is an illusion caused by the visual system and characterized by a visual perception, percept that arguably appears to differ from reality. Illusions come in a wide varie ...

. The antitail consists of larger dust particles left behind by the comet. These dust particles are less affected by the Sun's

radiation pressure Radiation pressure (also known as light pressure) is mechanical pressure exerted upon a surface due to the exchange of momentum between the object and the electromagnetic field. This includes the momentum of light or electromagnetic radiation of ...

and tend to remain roughly in the comet's

orbital plane The orbital plane of a revolving body is the geometric plane in which its orbit lies. Three non-collinear points in space suffice to determine an orbital plane. A common example would be the positions of the centers of a massive body (host) a ...

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. 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. 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, Comet Kohoutek in 1973,

Comet Hale–Bopp Comet Hale–Bopp (formally designated C/1995 O1) is a long-period comet that was one of the most widely observed of the 20th century and one of the brightest seen for many decades. Alan Hale (astronomer), Alan Hale and Thomas Bopp disc ...

in 1997, C/1999 H1 (Lee) in 1999, Comet Lulin in 2009, Comet PANSTARRS in 2013, C/2022 E3 (ZTF) in 2023, 12P/Pons–Brooks in 2024 and C/2023 A3 Tsuchinshan–ATLAS in 2024.

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Photo of Comet Arend–Roland in 1957 with prominent antitail.
Comets {{comet-stub

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