Procyon (α CMi / α Canis Minoris /
AlphaAlpha is the first letter of the Greek alphabet. In the system of Greek numerals it has a value of 1. It was derived from the Phoenician letter Aleph...
Canis Minoris) is the brightest
starA star is a massive, luminous ball of plasma that is held together by gravity. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth. Other stars are visible in the night sky, when they are not outshone by the Sun...
in the
constellationIn modern astronomy, a constellation is an area of the celestial sphere, defined by exact boundaries.The term "constellation" can also be used loosely to refer to just the more prominent visible stars that seem to form a pattern in that area.-Definitions:...
Canis MinorCanis Minor is a small constellation. It was included in the 2nd century astronomer Ptolemy's 48 constellations, and is still included among the 88 modern constellations...
. To the naked eye, it appears to be a single star, the
seventh brightest in the night sky with a visual
apparent magnitudeThe apparent magnitude of a celestial body is a measure of its brightness as seen by an observer on Earth, normalized to the value it would have in the absence of the atmosphere...
of 0.34. It is actually a
binary starA 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...
system, consisting of a white
main sequenceThe main sequence is a continuous and distinctive band of stars that appear 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...
star of spectral type F5 IV-V, named
Procyon A, and a faint
white dwarfA white dwarf, also called a degenerate dwarf, is a small star composed mostly of electron-degenerate matter. They are very dense; a white dwarf's mass is comparable to that of the Sun and its volume is comparable to that of the Earth. Its faint luminosity comes from the emission of stored...
companion of spectral type DA, named
Procyon B.
Procyon (α CMi / α Canis Minoris /
AlphaAlpha is the first letter of the Greek alphabet. In the system of Greek numerals it has a value of 1. It was derived from the Phoenician letter Aleph...
Canis Minoris) is the brightest
starA star is a massive, luminous ball of plasma that is held together by gravity. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth. Other stars are visible in the night sky, when they are not outshone by the Sun...
in the
constellationIn modern astronomy, a constellation is an area of the celestial sphere, defined by exact boundaries.The term "constellation" can also be used loosely to refer to just the more prominent visible stars that seem to form a pattern in that area.-Definitions:...
Canis MinorCanis Minor is a small constellation. It was included in the 2nd century astronomer Ptolemy's 48 constellations, and is still included among the 88 modern constellations...
. To the naked eye, it appears to be a single star, the
seventh brightest in the night sky with a visual
apparent magnitudeThe apparent magnitude of a celestial body is a measure of its brightness as seen by an observer on Earth, normalized to the value it would have in the absence of the atmosphere...
of 0.34. It is actually a
binary starA 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...
system, consisting of a white
main sequenceThe main sequence is a continuous and distinctive band of stars that appear 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...
star of spectral type F5 IV-V, named
Procyon A, and a faint
white dwarfA white dwarf, also called a degenerate dwarf, is a small star composed mostly of electron-degenerate matter. They are very dense; a white dwarf's mass is comparable to that of the Sun and its volume is comparable to that of the Earth. Its faint luminosity comes from the emission of stored...
companion of spectral type DA, named
Procyon B. The reason for its brightness is not its intrinsic luminosity but its closeness to the
SunThe Sun is the star at the center of the Solar System. The Earth and other matter orbit the Sun, which by itself accounts for about 99.86% of the Solar System's mass....
; at a distance of 3.5
pcThe parsec is a unit of length, equal to just under 31 million million kilometres , or about 3.26 light-years. The parsec measurement unit is used in astronomy and is defined as the length of the adjacent side of an imaginary right triangle in space...
or 11.41 light years, Procyon is one of our
near neighbours. Its closest neighbour is
Luyten's starLuyten's Star is a red dwarf star in the constellation Canis Minor. It is located at a distance of around 12.36 light-years and has a visual magnitude of 9.9, making it too faint to be viewed with the unaided eye. It is named after Willem Jacob Luyten, who first determined its proper motion.This...
, 0.34 pc or 1.11 ly away.
Procyon forms one of the three
verticesIn geometry, a vertex is a special kind of point which describes the corners or intersections of geometric shapes. Vertices are commonly used in computer graphics to define the corners of surfaces in 3D models, where each such point is given as a vector.-Of an angle:The vertex of an angle is the...
of the Winter Triangle, along with
SiriusSirius is the brightest star in the night sky with a visual apparent magnitude of −1.46, almost twice as bright as Canopus, the next brightest star. The name Sirius is derived from the Ancient Greek Σείριος. The star has the Bayer designation α Canis Majoris...
and
BetelgeuseBetelgeuse is a semiregular variable star located approximately 640 light-years from the Earth. It is Alpha Orionis , but the second brightest star in the constellation Orion and the ninth brightest star in the night sky...
.
System
Procyon A is a white star of spectral type F5; it is 1.4 times the mass, twice the diameter, and 7.5 times more
luminousLuminosity is a measurement of brightness usually denoted in Lumens.-In photometry and color imaging:In photometry, luminosity is sometimes incorrectly used to refer to luminance, which is the density of luminous intensity in a given direction...
than the
SunThe Sun is the star at the center of the Solar System. The Earth and other matter orbit the Sun, which by itself accounts for about 99.86% of the Solar System's mass....
. It is bright for its spectral class, suggesting that it is a
subgiant that has completely
fusedIn nuclear physics and nuclear chemistry, nuclear fusion is the process by which multiple like-charged atomic nuclei join together to form a heavier nucleus...
its core hydrogen into helium, and begun to expand as "burning" moves outside the core. As it continues to expand, the star will eventually swell to about 80 to 150 times its current diameter and become a red or orange color. This will probably happen within 10 to 100 million years. It is expected that the Sun will also go through this process when hydrogen fusion ceases at its core.
Like Sirius B, Procyon's companion is a white dwarf that was inferred from
astrometricAstrometry is the branch of astronomy that relates to precise measurements and explanations of the positions and movements of stars and other celestial bodies...
data long before it was observed. Its existence had been postulated by
Friedrich BesselFriedrich Wilhelm Bessel was a German mathematician, astronomer, and systematizer of the Bessel functions . He was a contemporary of Carl Gauss, also a mathematician and astronomer...
as early as 1844, and although its orbital elements had been calculated by
Arthur AuwersGeorg Friedrich Julius Arthur von Auwers was a German astronomer.Auwers was born in Göttingen, attended the University of Göttingen and worked at the University of Königsberg. He specialized in astrometry, making very precise measurements of stellar positions and motions...
in 1862 as part of his thesis, Procyon B was not visually confirmed until 1896 when
John Martin SchaeberleJohn Martin Schaeberle was a German-American astronomer. He was born Johann Martin Schäberle in Germany but immigrated as an infant to the United States. Most sources refer to him as John M...
observed it at the predicted position using the 36-inch refractor at
Lick ObservatoryThe Lick Observatory is an astronomical observatory, owned and operated by the University of California. It is situated on the summit of Mount Hamilton, in the Diablo Range just east of San Jose, California, USA...
. It is even more difficult to observe from Earth than Sirius B, due to a greater
apparent magnitudeThe apparent magnitude of a celestial body is a measure of its brightness as seen by an observer on Earth, normalized to the value it would have in the absence of the atmosphere...
difference and smaller angular separation from its primary.
The average separation of the two components is 15
AUAn astronomical unit is a unit of length roughly equal to the mean distance between the Earth and the Sun. It is approximately 150 million kilometres ....
s, a little less than the distance between
UranusUranus is the seventh planet from the Sun, and the third-largest and fourth most massive planet in the Solar System. It is named after the ancient Greek deity of the sky Uranus the father of Kronos and grandfather of Zeus...
and the Sun, though the eccentric orbit carries them as close as 9 AUs and as far as 21.
At 0.6
solar massThe solar mass , , is a standard way to express mass in astronomy, used to describe the masses of other stars and galaxies. It is equal to the mass of the Sun, about two nonillion kilograms or about 332,950 times the mass of the Earth or 1,048 times the mass of Jupiter.The solar mass can be...
es, Procyon B is considerably less massive than Sirius B; however, the peculiarities of
degenerate matterDegenerate matter is matter which has such extraordinarily high density that the dominant contribution to its pressure rises from the Pauli exclusion principle. The pressure maintained by a body of degenerate matter is called the degeneracy pressure, and arises because the Pauli principle prevents...
ensure that it is larger than its more famous neighbor, with an estimated radius of ~8,600 km, versus ~5,800 km for Sirius B. With a surface temperature of 7,740
KThe kelvin is a unit increment of temperature and is one of the seven SI base units. The Kelvin scale is a thermodynamic temperature scale where absolute zero, the theoretical absence of all thermal energy, is zero kelvin...
, it is also much cooler than Sirius B; this is a testament to its lesser mass and greater age.
Oscillations controversy
In late June 2004,
CanadaCanada is a country occupying most of northern North America, extending from the Atlantic Ocean in the east to the Pacific Ocean in the west and northward into the Arctic Ocean...
's orbital MOST satellite telescope carried out a 32-day survey of Procyon A. The continuous optical monitoring was intended to confirm
solar-like oscillationsThe term solar-like oscillations refers to oscillations in other stars that are excited in the same way as those in the Sun, namely by convection in its outer layers.-See also:* asteroseismology* helioseismology* variable stars* Procyon...
in its brightness observed from Earth and to permit
asteroseismologyAsteroseismology also known as Stellar seismology is the science that studies the internal structure of pulsating stars by the interpretation of their frequency spectra. Different oscillation modes penetrate to different depths inside the star...
. No oscillations were detected and the authors concluded that the theory of stellar oscillations may need to be reconsidered. However others argued that the non-detection was consistent with published ground-based
radial velocityRadial velocity is the velocity of an object in the direction of the line of sight . The light of an object with a substantial radial velocity will be subject to Doppler effect, so the frequency of the light decreases for receding objects and increases for approaching objects .The radial velocity...
observations of
solar-like oscillationsThe term solar-like oscillations refers to oscillations in other stars that are excited in the same way as those in the Sun, namely by convection in its outer layers.-See also:* asteroseismology* helioseismology* variable stars* Procyon...
.
Photometric measurements from the
NASAThe National Aeronautics and Space Administration is an agency of the United States government, responsible for the nation's public space program. NASA was established by the National Aeronautics and Space Act on July 29, 1958, replacing its predecessor, the National Advisory Committee for...
Wide Field Infrared ExplorerThe Wide Field Infrared Explorer is a satellite launched on 5 March 1999 on the Pegasus XL rocket into a polar orbit between 409 km and 426 km above the Earth's surface. WIRE was intended to be a four-month infrared survey of the entire sky, specifically focusing on starburst galaxies and luminous...
(WIRE) satellite from 1999 and 2000 showed evidence of granulation (
convectionConvection is the movement of molecules within fluids . Convection is one of the major modes of heat transfer and mass transfer...
near the surface of the
starA star is a massive, luminous ball of plasma that is held together by gravity. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth. Other stars are visible in the night sky, when they are not outshone by the Sun...
) and
solar-like oscillationsThe term solar-like oscillations refers to oscillations in other stars that are excited in the same way as those in the Sun, namely by convection in its outer layers.-See also:* asteroseismology* helioseismology* variable stars* Procyon...
. Unlike the MOST result, the variation seen in the WIRE
photometryPhotometry can refer to:*Photometry , the science of measurement of visible light in terms of its perceived brightness to human vision*Photometry , the measurement of the flux or intensity of an astronomical object's electromagnetic radiation...
was in agreement with
radial velocityRadial velocity is the velocity of an object in the direction of the line of sight . The light of an object with a substantial radial velocity will be subject to Doppler effect, so the frequency of the light decreases for receding objects and increases for approaching objects .The radial velocity...
measurements from the ground.
Etymology and cultural significance
Its name comes from the Greek
προκύον (
prokyon), meaning "before the dog", since it precedes the "Dog Star"
SiriusSirius is the brightest star in the night sky with a visual apparent magnitude of −1.46, almost twice as bright as Canopus, the next brightest star. The name Sirius is derived from the Ancient Greek Σείριος. The star has the Bayer designation α Canis Majoris...
as it travels across the sky due to
EarthEarth is the third planet from the Sun. It is the fifth largest of the eight planets in the solar system, and the largest of the terrestrial planets in the Solar System in terms of diameter, mass and density...
's rotation. (Although Procyon has a greater
right ascensionRight ascension is the astronomical term for one of the two coordinates of a point on the celestial sphere when using the equatorial coordinate system. The other coordinate is the declination.-Explanation:...
, it also has a more northerly
declinationIn astronomy, declination is one of the two coordinates of the equatorial coordinate system, the other being either right ascension or hour angle. Dec is comparable to latitude, projected onto the celestial sphere, and is measured in degrees north and south of the celestial equator...
, which means it will rise above the
horizonThe horizon is the apparent line that separates earth from sky.It is the line that divides all visible directions into two categories: those that intersect the Earth's surface, and those that do not...
earlier than Sirius from most northerly latitudes.) These two
dog starDog Star or Dogstar can refer to:* The "Dog Star" Sirius in the constellation of Canis Major* The Dogstar is a bar/music venue in Brixton, London...
s are referred to in the most ancient literature and were venerated by the
BabylonBabylon was a city-state of ancient Mesopotamia, the remains of which are found in present-day Al Hillah, Babil Province, Iraq, about 85 kilometers south of Baghdad...
ians and the
EgyptEgypt , officially the Arab Republic of Egypt, is a country mainly in North Africa, with the Sinai Peninsula forming a land bridge in Western Asia...
ians.
Rarer names are the Latin translation of Procyon,
Antecanis, and the Arabic-derived names
Al Shira and
Elgomaisa. The first derives from الشعرى الشامية
aš-ši‘ra aš-šamiyah "the Syrian sign" (the other sign being Sirius; "Syria" is supposedly a reference to its northern location relative to Sirius); the second from الغميصاء
al-ghumaisa’ "the bleary-eyed (woman)", in contrast to العبور "the teary-eyed (woman)", which is Sirius. (See Gomeisa.) The modern Arabic name for Procyon is غموص
ghumūş. It is known as 南河三 (Mandarin
nánhésān, the Third Star in the Southern River) in Chinese.
See also
External links