Antares
Encyclopedia
Antares is a red supergiant
star
in the Milky Way
galaxy
and the sixteenth brightest star in the nighttime sky (sometimes listed as 15th brightest, if the two brighter components of the Capella
quadruple star system are counted as one star). Along with Aldebaran
, Spica
, and Regulus
it is one of the four brightest stars near the ecliptic
. Antares is a slow variable star with an average magnitude
of +1.09.
Antares is a class M
supergiant star, with a radius of approximately 800 times that of the sun; if it were placed in the center of our solar system, its outer surface would lie between the orbits of Mars and Jupiter. Antares is approximately 600 ly from our solar system. Its visual luminosity
is about 10,000 times that of the Sun
, but because the star radiates a considerable part of its energy in the infrared
part of the spectrum
, the bolometric
luminosity equals roughly 65,000 times that of the Sun. The mass of the star is calculated to be 15 to 18 solar mass
es. Its large size and relatively small mass give Antares a very low average density.
The size of Antares may be calculated using its parallax and angular diameter. The parallax angle is given in the box to the right, and the angular diameter is known from lunar occultation measurements (41.3 ± 0.1 mas). This leads to a radius of 822 ± 80 solar radii.
Antares is a type LC slow irregular variable
star, whose apparent magnitude slowly varies from +0.88 to +1.16.
The best time to view Antares is on or around May 31 of each year, when the star is at opposition to the Sun
. At this time, Antares rises at dusk and sets at dawn, and is thus in view all night. For approximately two to three weeks on either side of November 30, Antares is not visible in the night sky, being lost in the Sun's glare; this period of invisibility is longer in the Northern Hemisphere
than in the Southern Hemisphere
, since the star's declination
is significantly south of the celestial equator.
at Antares' estimated distance. At magnitude 5.5, it is only 1/370th as bright visually as Antares A, although it shines with 170 times the Sun's luminosity. It is normally difficult to see in small telescopes due to Antares' glare, but can sometimes be seen in apertures over 150 mm (5.9 in). The companion is often described as green, but this is probably a contrast effect. Antares B can be observed with a small telescope
for a few seconds during lunar occultation
s while Antares itself is hidden by the Moon
; it was discovered by Johann Tobias Bürg
during one such occultation on April 13, 1819.
The orbit is poorly known, with an estimated period
of 878 years.
by the Moon and rarely by the planets. On 31 July 2009, Antares was occulted by the moon. The event was visible in much of southern Asia and the Middle East. Every year around December 2 the Sun passes 5° north of Antares.
, meaning "(holds) against Ares
(Mars)", due to the similarity of its red
dish hue to the appearance of the planet Mars
. It is the brightest star in the constellation
Scorpius
. However, it is also thought that Antares may have been named after the ancient Arab warrior-poet Antar
.
Its distinctive color has made the star an object of interest to many societies throughout history.
Alternative name of this star, meaning "the Heart of Scorpion":
Red supergiant
Red supergiants are supergiant stars of spectral type K or M. They are the largest stars in the universe in terms of volume, although they are not the most massive...
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 Milky Way
Milky Way
The Milky Way is the galaxy that contains the Solar System. This name derives from its appearance as a dim un-resolved "milky" glowing band arching across the night sky...
galaxy
Galaxy
A galaxy is a massive, gravitationally bound system that consists of stars and stellar remnants, an interstellar medium of gas and dust, and an important but poorly understood component tentatively dubbed dark matter. The word galaxy is derived from the Greek galaxias , literally "milky", a...
and the sixteenth brightest star in the nighttime sky (sometimes listed as 15th brightest, if the two brighter components of the Capella
Capella (star)
Capella is the brightest star in the constellation Auriga, the sixth brightest star in the night sky and the third brightest star in the northern celestial hemisphere, after Arcturus and Vega. Although it appears to be a single star to the naked eye, it is actually a star system of four stars in...
quadruple star system are counted as one star). Along with Aldebaran
Aldebaran
Aldebaran is a red giant star located about 65 light years away in the zodiac constellation of Taurus. With an average apparent magnitude of 0.87 it is the brightest star in the constellation and is one of the brightest stars in the nighttime sky...
, Spica
Spica
Spica is the brightest star in the constellation Virgo, and the 15th brightest star in the nighttime sky. It is 260 light years distant from Earth...
, and Regulus
Regulus
Regulus is the brightest star in the constellation Leo and one of the brightest stars in the night sky, lying approximately 77.5 light years from Earth. Regulus is a multiple star system composed of four stars which are organized into two pairs...
it is one of the four brightest stars near the ecliptic
Ecliptic
The ecliptic is the plane of the earth's orbit around the sun. In more accurate terms, it is the intersection of the celestial sphere with the ecliptic plane, which is the geometric plane containing the mean orbit of the Earth around the Sun...
. Antares is a slow variable star with an average 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 +1.09.
Properties
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...
supergiant star, with a radius of approximately 800 times that of the sun; if it were placed in the center of our solar system, its outer surface would lie between the orbits of Mars and Jupiter. Antares is approximately 600 ly from our solar system. Its visual luminosity
Luminosity
Luminosity is a measurement of brightness.-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. The SI unit for luminance is candela per square metre.The luminosity function...
is about 10,000 times that of the Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
, but because the star radiates a considerable part of its energy in the infrared
Infrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
part of the spectrum
Spectrum
A spectrum is a condition that is not limited to a specific set of values but can vary infinitely within a continuum. The word saw its first scientific use within the field of optics to describe the rainbow of colors in visible light when separated using a prism; it has since been applied by...
, the bolometric
Bolometer
A bolometer is a device for measuring the power of incident electromagnetic radiation via the heating of a material with a temperature-dependent electrical resistance. It was invented in 1878 by the American astronomer Samuel Pierpont Langley...
luminosity equals roughly 65,000 times that of the Sun. The mass of the star is calculated to be 15 to 18 solar mass
Solar mass
The solar mass , , is a standard unit of mass in astronomy, used to indicate the masses of other stars and galaxies...
es. Its large size and relatively small mass give Antares a very low average density.
The size of Antares may be calculated using its parallax and angular diameter. The parallax angle is given in the box to the right, and the angular diameter is known from lunar occultation measurements (41.3 ± 0.1 mas). This leads to a radius of 822 ± 80 solar radii.
Antares is a type LC slow irregular variable
Slow irregular variable
A slow irregular variable is a variable star that exhibit no or very poorly defined periodicity in their slowly changing light emissions. Most of them are late spectral types K and M, S stars or carbon stars...
star, whose apparent magnitude slowly varies from +0.88 to +1.16.
The best time to view Antares is on or around May 31 of each year, when the star is at opposition to the Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
. At this time, Antares rises at dusk and sets at dawn, and is thus in view all night. For approximately two to three weeks on either side of November 30, Antares is not visible in the night sky, being lost in the Sun's glare; this period of invisibility is longer in the Northern Hemisphere
Northern Hemisphere
The Northern Hemisphere is the half of a planet that is north of its equator—the word hemisphere literally means “half sphere”. It is also that half of the celestial sphere north of the celestial equator...
than in the Southern Hemisphere
Southern Hemisphere
The Southern Hemisphere is the part of Earth that lies south of the equator. The word hemisphere literally means 'half ball' or "half sphere"...
, since the star's declination
Declination
In astronomy, declination is one of the two coordinates of the equatorial coordinate system, the other being either right ascension or hour angle. Declination in astronomy is comparable to geographic latitude, but projected onto the celestial sphere. Declination is measured in degrees north and...
is significantly south of the celestial equator.
Companion star
Antares has a hot blue companion star, Antares B, of spectral type B2.5 at a separation of about 2.9 arcseconds, or 550 AUsAstronomical unit
An astronomical unit is a unit of length equal to about or approximately the mean Earth–Sun distance....
at Antares' estimated distance. At magnitude 5.5, it is only 1/370th as bright visually as Antares A, although it shines with 170 times the Sun's luminosity. It is normally difficult to see in small telescopes due to Antares' glare, but can sometimes be seen in apertures over 150 mm (5.9 in). The companion is often described as green, but this is probably a contrast effect. Antares B can be observed with a small telescope
Telescope
A telescope is an instrument that aids in the observation of remote objects by collecting electromagnetic radiation . The first known practical telescopes were invented in the Netherlands at the beginning of the 1600s , using glass lenses...
for a few seconds during lunar occultation
Occultation
An occultation is an event that occurs when one object is hidden by another object that passes between it and the observer. The word is used in astronomy . It can also refer to any situation wherein an object in the foreground blocks from view an object in the background...
s while Antares itself is hidden by the Moon
Moon
The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...
; it was discovered by Johann Tobias Bürg
Johann Tobias Bürg
Johann Tobias Bürg was an Austrian astronomer.Born in Vienna, Bürg worked as a professor and astronomer in Klagenfurt, in Carinthia. He subsequently worked as astronomical assistant at the observatory at Vienna from 1792 until he retired in 1813.He published some astronomical tables on the Moon...
during one such occultation on April 13, 1819.
The orbit is poorly known, with an estimated period
Orbital period
The orbital period is the time taken for a given object to make one complete orbit about another object.When mentioned without further qualification in astronomy this refers to the sidereal period of an astronomical object, which is calculated with respect to the stars.There are several kinds of...
of 878 years.
Position on the ecliptic
Antares is one of the 4 first magnitude stars that lies within 5° of the ecliptic and therefore can be occultedOccultation
An occultation is an event that occurs when one object is hidden by another object that passes between it and the observer. The word is used in astronomy . It can also refer to any situation wherein an object in the foreground blocks from view an object in the background...
by the Moon and rarely by the planets. On 31 July 2009, Antares was occulted by the moon. The event was visible in much of southern Asia and the Middle East. Every year around December 2 the Sun passes 5° north of Antares.
Traditional names
Antares, the proper name of this star, derives from the Ancient GreekAncient Greek
Ancient Greek is the stage of the Greek language in the periods spanning the times c. 9th–6th centuries BC, , c. 5th–4th centuries BC , and the c. 3rd century BC – 6th century AD of ancient Greece and the ancient world; being predated in the 2nd millennium BC by Mycenaean Greek...
, meaning "(holds) against Ares
Ares
Ares is the Greek god of war. He is one of the Twelve Olympians, and the son of Zeus and Hera. In Greek literature, he often represents the physical or violent aspect of war, in contrast to the armored Athena, whose functions as a goddess of intelligence include military strategy and...
(Mars)", due to the similarity of its red
Red
Red is any of a number of similar colors evoked by light consisting predominantly of the longest wavelengths of light discernible by the human eye, in the wavelength range of roughly 630–740 nm. Longer wavelengths than this are called infrared , and cannot be seen by the naked eye...
dish hue to the appearance of the planet Mars
Mars
Mars is the fourth planet from the Sun in the Solar System. The planet is named after the Roman god of war, Mars. It is often described as the "Red Planet", as the iron oxide prevalent on its surface gives it a reddish appearance...
. It is the brightest star 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....
Scorpius
Scorpius
Scorpius, sometimes known as Scorpio, is one of the constellations of the zodiac. Its name is Latin for scorpion, and its symbol is . It lies between Libra to the west and Sagittarius to the east...
. However, it is also thought that Antares may have been named after the ancient Arab warrior-poet Antar
Antarah ibn Shaddad
'Antarah Ibn Shaddād al-'Absī عنترة بن شداد العبسي was a pre-Islamic Arabian hero and poet famous both for his poetry and his adventurous life. What many consider his best or chief poem is contained in the Mu'allaqat...
.
Its distinctive color has made the star an object of interest to many societies throughout history.
- In Persia, Antares was known as Satevis, one of the four "royal starsRoyal starsThe four Royal stars or Guardians of the Sky were a group of stars noticed by the Persian astrologers, and mentioned by Zarathustra , around 3000 BC and used as a rudimentary season calendar....
". - In IndiaIndiaIndia , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...
, it with σSigma ScorpiiSigma Scorpii is a star system in the constellation Scorpius. It has the traditional name Al Niyat, although this name is sometimes also applied to Tau Scorpii, or to the asterism formed by both Sigma and Tau. Sigma Scorpii is 735 light years from the Sun.The primary component of the system,...
and τ ScoTau ScorpiiTau Scorpii is a star in the constellation Scorpius. Tau Scorpii also has the traditional name Alniyat or Al Niyat, which it shares with σ Scorpii. The name derives from the Arabic النياط an-niyāţ meaning "the arteries"....
were one of nakshatraNakshatraNakshatra is the term for lunar mansion in Hindu astrology. A nakshatra is one of 27 sectors along the ecliptic...
(HinduHinduHindu refers to an identity associated with the philosophical, religious and cultural systems that are indigenous to the Indian subcontinent. As used in the Constitution of India, the word "Hindu" is also attributed to all persons professing any Indian religion...
lunar mansionLunar mansionA lunar mansion is a segment of the ecliptic through which the moon moves in its orbit around the earth, often used by ancient cultures as part of their calendar system...
), as Jyeshthā "Oldest", and Rohinī "Ruddy". - In ChinaChinaChinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...
, it was named 心宿二 (Mandarin: xīn sù èr), because it was the second star of the asterism 心宿 ("Heart"). - Antares is listed in MUL.APINMUL.APINMUL.APIN is the conventional title given to a Babylonian compendium that deals with many diverse aspects of Babylonian astronomy and astrology....
as GABA GIR.TAB, meaning "the Breast of the Scorpion:Lishi, Nabu". - In Renaissance astrology, Antares is one of the Behenian fixed starBehenian fixed starThe Behenian fixed stars are a selection of fifteen stars considered especially useful for magical applications in the medieval astrology of Europe and the Arab world. Their name derives from Arabic bahman, "root," as each was considered a source of astrological power for one or more planets...
s and has the symbol
. - The Wotjobaluk KooriKooriThe Koori are the indigenous Australians that traditionally occupied modern day New South Wales and Victoria....
people of Victoria, Australia, knew Antares as Djuit, son of Marpean-kurrk (Arcturus); the stars on each side represented his wives. The Kulin Kooris saw Antares (Balayang) as the brother of Bunjil (Altair).
Alternative name of this star, meaning "the Heart of Scorpion":
- from the Arabic . This had been directly translated from the Ancient GreekAncient GreekAncient Greek is the stage of the Greek language in the periods spanning the times c. 9th–6th centuries BC, , c. 5th–4th centuries BC , and the c. 3rd century BC – 6th century AD of ancient Greece and the ancient world; being predated in the 2nd millennium BC by Mycenaean Greek...
. - translated above Greek name into LatinLatinLatin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...
.