Zeta Cancri (ζ Cancri, abbreviated Zeta Cnc, ζ Cnc) is a multiple
star system
A star system or stellar system is a small number of stars that orbit each other, bound by gravitational attraction. A large group of stars bound by gravitation is generally called a '' star cluster'' or '' galaxy'', although, broadly speak ...
in the
constellation
A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object.
The origins of the e ...
of
Cancer
Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. These contrast with benign tumors, which do not spread. Possible signs and symptoms include a lump, abnormal b ...
. It is approximately 83.4
light-year
A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distances and is equivalent to about 9.46 trillion kilometers (), or 5.88 trillion miles ().One trillion here is taken to be 1012 ...
s from
Earth
Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...
, and has a combined
apparent magnitude
Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's li ...
of +4.67. Since it is near the
ecliptic
The ecliptic or ecliptic plane is the orbital plane of the Earth around the Sun. From the perspective of an observer on Earth, the Sun's movement around the celestial sphere over the course of a year traces out a path along the ecliptic again ...
, it can be
occulted by the
Moon
The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...
and, very rarely, by
planet
A planet is a large, rounded astronomical body that is neither a star nor its remnant. The best available theory of planet formation is the nebular hypothesis, which posits that an interstellar cloud collapses out of a nebula to create a you ...
s.
The system is constituted as follows:
* A
binary pair designated Zeta
1 Cancri or, alternatively, Zeta Cancri AB, the two components of which are themselves designated Zeta
1 Cancri A or, simply, Zeta Cancri A (formally also named Tegmine , the traditional name of the Zeta Cancri system)
and Zeta
1/Zeta Cancri B.
* A
triple star system
A star system or stellar system is a small number of stars that orbit each other, bound by gravitational attraction. A large group of stars bound by gravitation is generally called a ''star cluster'' or ''galaxy'', although, broadly speaking, ...
designated Zeta
2 Cancri or alternatively Zeta Cancri C, consisting of a single star primary, designated Zeta
2/Zeta Cancri Ca, together with a secondary binary pair, designated Zeta
2/Zeta Cancri Cb. The binary pair's two components are themselves designated Zeta
2/Zeta Cancri Cb1 and Cb2.
Nomenclature
''ζ Cancri'' (
Latinised to ''Zeta Cancri'') is the system's
Bayer designation
A Bayer designation is a stellar designation in which a specific star is identified by a Greek or Latin letter followed by the genitive form of its parent constellation's Latin name. The original list of Bayer designations contained 1,564 stars. ...
; ''ζ
1 Cancri'' and ''ζ
2 Cancri'' those of its two constituents. The designations of the two constituents as ''ζ Cancri AB'' and ''C'', and those of their components—''ζ Cancri A'', ''B'', ''Ca'', ''Cb'', ''Cb1'' and ''Cb2''—derive from the convention used by the Washington Multiplicity Catalog (WMC) for
multiple star system
A star system or stellar system is a small number of stars that orbit each other, bound by gravitational attraction. A large group of stars bound by gravitation is generally called a '' star cluster'' or '' galaxy'', although, broadly speaki ...
s, and adopted by the
International Astronomical Union
The International Astronomical Union (IAU; french: link=yes, Union astronomique internationale, UAI) is a nongovernmental organisation with the objective of advancing astronomy in all aspects, including promoting astronomical research, outreac ...
(IAU).
Considerable confusion had developed concerning the catalogue identities of the three bright stars; correct correspondences were worked out by Griffin:
''Zeta Cancri'' bore the traditional name ''Tegmine'' (''Tegmen'') "the shell (of the crab)". In 2016, the
International Astronomical Union
The International Astronomical Union (IAU; french: link=yes, Union astronomique internationale, UAI) is a nongovernmental organisation with the objective of advancing astronomy in all aspects, including promoting astronomical research, outreac ...
organized a
Working Group on Star Names
The International Astronomical Union (IAU) established a Working Group on Star Names (WGSN) in May 2016 to catalog and standardize proper names for stars for the international astronomical community. It operates under Division C – Education ...
(WGSN)
to catalogue and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire
multiple systems.
It approved the name ''Tegmine'' for the component ''Zeta
1 Cancri A'' on 12 September 2016 and it is now so included in the List of IAU-approved Star Names.
In
Chinese
Chinese can refer to:
* Something related to China
* Chinese people, people of Chinese nationality, citizenship, and/or ethnicity
**''Zhonghua minzu'', the supra-ethnic concept of the Chinese nation
** List of ethnic groups in China, people of va ...
, (), meaning ''
Water Level
Water level, also known as gauge height or stage, is the elevation of the free surface of a sea, stream, lake or reservoir relative to a specified vertical datum.ISO 772: 1996. Hydrometric determinations – Vocabulary and symbols.
See also
* ...
'', refers to an
asterism consisting of Zeta Cancri,
6 Canis Minoris,
11 Canis Minoris and
8 Cancri. Consequently, Zeta Cancri itself is known as (, en, the Fourth Star of Water Level).
[香港太空館 - 研究資源 - 亮星中英對照表]
, Hong Kong Space Museum. Accessed on line November 23, 2010.
Properties
Zeta Cancri can be resolved as a binary star in small telescopes. Its binary nature was discovered in 1756 by
Tobias Mayer
Tobias Mayer (17 February 172320 February 1762) was a German astronomer famous for his studies of the Moon.
He was born at Marbach, in Württemberg, and brought up at Esslingen in poor circumstances. A self-taught mathematician, he earned a l ...
.
William Herschel
Frederick William Herschel (; german: Friedrich Wilhelm Herschel; 15 November 1738 – 25 August 1822) was a German-born British astronomer and composer. He frequently collaborated with his younger sister and fellow astronomer Caroline H ...
resolved the two components that make up Zeta
1 Cancri in 1781. As early as 1831,
John Herschel
Sir John Frederick William Herschel, 1st Baronet (; 7 March 1792 – 11 May 1871) was an English polymath active as a mathematician, astronomer, chemist, inventor, experimental photographer who invented the blueprint and did botanical wor ...
noticed
perturbations in Zeta
2 Cancri's
orbit
In celestial mechanics, an orbit is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an object or position in space such as a p ...
around Zeta
1; this led
Otto Wilhelm von Struve
Otto Wilhelm von Struve (May 7, 1819 (Julian calendar: April 25) – April 14, 1905) was a Russian astronomer of Baltic German origins. In Russian, his name is normally given as Otto Vasil'evich Struve (Отто Васильевич Струве ...
, in 1871, to postulate a fourth, unseen, component which orbited closely the visible member of Zeta
2.
Later observations have resolved this fourth component and have indicated that there may be one or two more unobserved components.
[
Zeta1 and Zeta2 Cancri are 5.06 ]arcsecond
A minute of arc, arcminute (arcmin), arc minute, or minute arc, denoted by the symbol , is a unit of angular measurement equal to of one degree. Since one degree is of a turn (or complete rotation), one minute of arc is of a turn. The na ...
s apart. These two star systems orbit around their common centre of mass
In physics, the center of mass of a distribution of mass in space (sometimes referred to as the balance point) is the unique point where the weighted relative position of the distributed mass sums to zero. This is the point to which a force may ...
once every 1,100 years.
Zeta1 Cancri
The two components are both yellow-white main-sequence
In astronomy, the main sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. These color-magnitude plots are known as Hertzsprung–Russell diagrams after their co-developers, Ejnar Hert ...
dwarfs of spectral class F. The apparent magnitude
Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's li ...
s of A and B are +5.58 and +5.99, respectively. They are separated, as of 2008, by 1 arcsecond
A minute of arc, arcminute (arcmin), arc minute, or minute arc, denoted by the symbol , is a unit of angular measurement equal to of one degree. Since one degree is of a turn (or complete rotation), one minute of arc is of a turn. The na ...
, requiring a large telescope to resolve them, but this separation will increase until the year 2020. They complete one orbit every 59.6 years. The estimated masses for the pair are 1.28 and 1.18 solar mass
The solar mass () is a standard unit of mass in astronomy, equal to approximately . It is often used to indicate the masses of other stars, as well as stellar clusters, nebulae, galaxies and black holes. It is approximately equal to the mass ...
es, respectively.
Zeta2 Cancri
Zeta Cancri Ca is the brightest of the three components, having an apparent magnitude of +6.12. It appears to be a yellow G-type star
A G-type main-sequence star (Spectral type: G-V), also often, and imprecisely called a yellow dwarf, or G star, is a main-sequence star (luminosity class V) of spectral type G. Such a star has about 0.9 to 1.1 solar masses and an effective tempe ...
, often reported as G5V, but now thought to be earlier, probably G0V. This star has around 1.15 solar mass
The solar mass () is a standard unit of mass in astronomy, equal to approximately . It is often used to indicate the masses of other stars, as well as stellar clusters, nebulae, galaxies and black holes. It is approximately equal to the mass ...
es.[ The tenth magnitude Zeta Cancri Cb is a close pair of ]red dwarf
''Red Dwarf'' is a British science fiction comedy franchise created by Rob Grant and Doug Naylor, which primarily consists of a television sitcom that aired on BBC Two between 1988 and 1999, and on Dave since 2009, gaining a cult following. T ...
s. The separation between Ca and Cb is approximately 0.3 arcsecond
A minute of arc, arcminute (arcmin), arc minute, or minute arc, denoted by the symbol , is a unit of angular measurement equal to of one degree. Since one degree is of a turn (or complete rotation), one minute of arc is of a turn. The na ...
, and their orbital period
The orbital period (also revolution period) is the amount of time a given astronomical object takes to complete one orbit around another object. In astronomy, it usually applies to planets or asteroids orbiting the Sun, moons orbiting planets ...
is 17 years.
References
{{Stars of Cancer
Cancer (constellation)
Cancri, Zeta
Cancri, 16
5
F-type main-sequence stars
G-type main-sequence stars
M-type main-sequence stars
Tegmine
Durchmusterung objects
040167
3208 09 10
068255 6 7