Beta Cassiopeiae
Encyclopedia
Beta Cassiopeiae (β Cas, β Cassiopeiae) is a Delta Scuti variable
star
in the constellation
Cassiopeia
. It is a subgiant or giant
star belonging to the spectral class F2, with a mean apparent magnitude
of +2.27 and absolute magnitude of +1.16. It has the traditional name Caph, from the Arabic word , "palm" (i.e. reaching from the Pleiades), also known as . Another Arabic name is al-Kaff al-Khadib.
(V-band
) of +2.27, it is one of the five stars which make up the 'W' of Cassiopeia, adjacent to the just brighter Schedar (Alpha Cassiopeiae
). SN 1572
, traditionally known as Tycho's Star, appeared about 5 degrees to the northwest of Caph in 1572.
As a star in the deep northern hemisphere of the sky, Beta Cassiopeiae is prominent to viewers in the northern hemisphere but not often seen by those in the southern hemisphere. The constellation of Cassiopeia does not rise above the horizon to viewers in Tasmania, and only low if one were in Cairns.
of spectral class F2
, with a surface temperature of 6,700 Kelvin. Four times the size of and 28 times brighter than the sun, Caph has an absolute magnitude of +1.16. It was once a white A-type star about double the sun's mass. It is now in the process of cooling and growing to become a red giant
. Its core is likely to have used up its hydrogen and is shrinking and heating, while its outer envelope of hydrogen is expanding and cooling. Stars do not spend much time in this state and are relatively uncommon. Caph's corona
is unusually weak.
β Cassiopeiae is also a variable star
of the Delta Scuti type
, in fact the second brightest of them in the sky after Altair. Its brightness varies from magnitude +2.25 to +2.31 with a period of 2.5 hours. This type of variables includes subgiant or main sequence
stars of spectral classes F5–A0. Their pulsations are related to the same helium instability strip
on the Hertzsprung–Russell diagram
as that of classical Cepheids. Delta Scuti stars are located at the intersection of the strip with the main sequence.
β Cassiopeiae is a binary star
, with a faint companion, which orbits it every 27 days.
Alternate common names are Chaph and Kaff, as well as al-Sanam al-Nakah "the Camel's Hump".
In Chinese
, , meaning Wang Liang
, refers to an asterism consisting of β Cassiopeiae, κ Cassiopeiae
, η Cassiopeiae
, α Cassiopeiae
and λ Cassiopeiae
. Consequently, β Cassiopeiae itself is known as
Together with Alpha Andromedae
(Alpheratz) and Gamma Pegasi
(Algenib), Beta Cassiopeiae was one of three bright stars known as the "Three Guides" marking the equinoctial colure. This is an imaginary line running due south from Beta Cassiopeiae through Alpha Andromedae to the celestial equator, at a point where the sun's path (the ecliptic) crosses it each autumn and spring equinox.
Delta Scuti variable
A Delta Scuti variable is a variable star which exhibits variations in its luminosity due to both radial and non-radial pulsations of the star's surface. Typical brightness fluctuations are from 0.003 to 0.9 magnitudes in V over a period of a few hours, although the amplitude and period of the...
star
Star
A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
in the constellation
Constellation
In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....
Cassiopeia
Cassiopeia (constellation)
Cassiopeia is a constellation in the northern sky, named after the vain queen Cassiopeia in Greek mythology, who boasted about her unrivalled beauty. Cassiopea was one of the 48 constellations listed by the 2nd century Greek astronomer Ptolemy, and it remains one of the 88 modern constellations today...
. It is a subgiant or giant
Giant star
A giant star is a star with substantially larger radius and luminosity than a main sequence star of the same surface temperature. Typically, giant stars have radii between 10 and 100 solar radii and luminosities between 10 and 1,000 times that of the Sun. Stars still more luminous than giants are...
star belonging to the spectral class F2, with a mean apparent magnitude
Apparent magnitude
The apparent magnitude of a celestial body is a measure of its brightness as seen by an observer on Earth, adjusted to the value it would have in the absence of the atmosphere...
of +2.27 and absolute magnitude of +1.16. It has the traditional name Caph, from the Arabic word , "palm" (i.e. reaching from the Pleiades), also known as . Another Arabic name is al-Kaff al-Khadib.
Visibility
With a mean apparent magnitudeApparent magnitude
The apparent magnitude of a celestial body is a measure of its brightness as seen by an observer on Earth, adjusted to the value it would have in the absence of the atmosphere...
(V-band
UBV photometric system
UBV photometric system, also called the Johnson system , is a wide band photometric system for classifying stars according to their colors. It is the first known standardized photoelectric photometric system. The letters U, B, and V stand for ultraviolet, blue, and visual magnitudes, which are...
) of +2.27, it is one of the five stars which make up the 'W' of Cassiopeia, adjacent to the just brighter Schedar (Alpha Cassiopeiae
Alpha Cassiopeiae
Alpha Cassiopeiae is a second magnitude star in the constellation Cassiopeia, with the traditional name Schedar, sometimes spelt Shedir. Though listed as the alpha star by Johann Bayer, Schedar's visual brightness closely rivals the beta star in the constellation, Caph...
). SN 1572
SN 1572
SN 1572 , "B Cassiopeiae" , or 3C 10 was a supernova of Type Ia in the constellation Cassiopeia, one of about eight supernovae visible to the naked eye in historical records...
, traditionally known as Tycho's Star, appeared about 5 degrees to the northwest of Caph in 1572.
As a star in the deep northern hemisphere of the sky, Beta Cassiopeiae is prominent to viewers in the northern hemisphere but not often seen by those in the southern hemisphere. The constellation of Cassiopeia does not rise above the horizon to viewers in Tasmania, and only low if one were in Cairns.
System
β Cassiopeiae is classed as a yellow-white subgiant or giantGiant star
A giant star is a star with substantially larger radius and luminosity than a main sequence star of the same surface temperature. Typically, giant stars have radii between 10 and 100 solar radii and luminosities between 10 and 1,000 times that of the Sun. Stars still more luminous than giants are...
of spectral class F2
Stellar classification
In astronomy, stellar classification is a classification of stars based on their spectral characteristics. The spectral class of a star is a designated class of a star describing the ionization of its chromosphere, what atomic excitations are most prominent in the light, giving an objective measure...
, with a surface temperature of 6,700 Kelvin. Four times the size of and 28 times brighter than the sun, Caph has an absolute magnitude of +1.16. It was once a white A-type star about double the sun's mass. It is now in the process of cooling and growing to become a red giant
Red giant
A red giant is a luminous giant star of low or intermediate mass in a late phase of stellar evolution. The outer atmosphere is inflated and tenuous, making the radius immense and the surface temperature low, somewhere from 5,000 K and lower...
. Its core is likely to have used up its hydrogen and is shrinking and heating, while its outer envelope of hydrogen is expanding and cooling. Stars do not spend much time in this state and are relatively uncommon. Caph's corona
Corona
A corona is a type of plasma "atmosphere" of the Sun or other celestial body, extending millions of kilometers into space, most easily seen during a total solar eclipse, but also observable in a coronagraph...
is unusually weak.
β Cassiopeiae is also a variable star
Variable star
A star is classified as variable if its apparent magnitude as seen from Earth changes over time, whether the changes are due to variations in the star's actual luminosity, or to variations in the amount of the star's light that is blocked from reaching Earth...
of the Delta Scuti type
Delta Scuti variable
A Delta Scuti variable is a variable star which exhibits variations in its luminosity due to both radial and non-radial pulsations of the star's surface. Typical brightness fluctuations are from 0.003 to 0.9 magnitudes in V over a period of a few hours, although the amplitude and period of the...
, in fact the second brightest of them in the sky after Altair. Its brightness varies from magnitude +2.25 to +2.31 with a period of 2.5 hours. This type of variables includes subgiant or main sequence
Main sequence
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 Hertzsprung and Henry Norris Russell...
stars of spectral classes F5–A0. Their pulsations are related to the same helium instability strip
Instability strip
The Instability strip is a nearly vertical region in the Hertzsprung–Russell diagram which is occupied by pulsating variable stars .The instability strip intersects the main sequence in the region of A...
on the Hertzsprung–Russell diagram
Hertzsprung–Russell diagram
The Hertzsprung–Russell diagram is a scatter graph of stars showing the relationship between the stars' absolute magnitudes or luminosities versus their spectral types or classifications and effective temperatures. Hertzsprung–Russell diagrams are not pictures or maps of the locations of the stars...
as that of classical Cepheids. Delta Scuti stars are located at the intersection of the strip with the main sequence.
β Cassiopeiae is a binary star
Binary star
A binary star is a star system consisting of two stars orbiting around their common center of mass. The brighter star is called the primary and the other is its companion star, comes, or secondary...
, with a faint companion, which orbits it every 27 days.
Etymology and cultural significance
Originally, the pre-islamic Arabic term al-Kaff al-Khadib "the stained hand" referred to the five stars comprising the 'W' of the constellation Cassiopeia, and depicted a hand stained with henna. The term was abbreviated and somehow came to signify β Cassiopeiae alone. The old "stained hand" was part of an asterism stretching from the Pleiades, which signified the "head" through Taurus and Perseus and into Cassiopeia, while the other "hand" was in Cetus.Alternate common names are Chaph and Kaff, as well as al-Sanam al-Nakah "the Camel's Hump".
In Chinese
Chinese language
The Chinese language is a language or language family consisting of varieties which are mutually intelligible to varying degrees. Originally the indigenous languages spoken by the Han Chinese in China, it forms one of the branches of Sino-Tibetan family of languages...
, , meaning Wang Liang
Legs (Chinese constellation)
The Legs mansion is one of the Twenty-eight mansions of the Chinese constellations. It is one of the western mansions of the White Tiger.-Asterisms:...
, refers to an asterism consisting of β Cassiopeiae, κ Cassiopeiae
Kappa Cassiopeiae
Kappa Cassiopeiae is a star in the constellation Cassiopeia.κ Cassiopeiae is a blue-white B-type supergiant with a mean apparent magnitude of +4.17. It is approximately 4100 light years from Earth. It is classified as an Alpha Cygni type variable star and its brightness varies from magnitude...
, η Cassiopeiae
Eta Cassiopeiae
Eta Cassiopeiae is a star system 19.4 light years away from Earth, in the constellation Cassiopeia. Sometimes the traditional name Achird is used....
, α Cassiopeiae
Alpha Cassiopeiae
Alpha Cassiopeiae is a second magnitude star in the constellation Cassiopeia, with the traditional name Schedar, sometimes spelt Shedir. Though listed as the alpha star by Johann Bayer, Schedar's visual brightness closely rivals the beta star in the constellation, Caph...
and λ Cassiopeiae
Lambda Cassiopeiae
Lambda Cassiopeiae is a binary star in the constellation Cassiopeia. The system has a combined apparent magnitude of +4.74 and is approximately 355 light years from Earth....
. Consequently, β Cassiopeiae itself is known as
Together with Alpha Andromedae
Alpha Andromedae
Alpha Andromedae , which has the traditional names Alpheratz and Sirrah , is the brightest star in the constellation of Andromeda. Located immediately northeast of the constellation of Pegasus, it is the northeastern star of the Great Square of Pegasus...
(Alpheratz) and Gamma Pegasi
Gamma Pegasi
Gamma Pegasi is a star in the constellation of Pegasus. It also has the traditional name Algenib; confusingly however, this name is also used for Alpha Persei....
(Algenib), Beta Cassiopeiae was one of three bright stars known as the "Three Guides" marking the equinoctial colure. This is an imaginary line running due south from Beta Cassiopeiae through Alpha Andromedae to the celestial equator, at a point where the sun's path (the ecliptic) crosses it each autumn and spring equinox.