Achernar
Encyclopedia
Achernar sometimes spelled Achenar, is the brightest star in the constellation
Eridanus
and the ninth-brightest star in the night sky. Of the top ten apparent brightest stars (excluding our Sun)—Sirius
, Canopus
, Alpha Centauri
, Arcturus, Vega
, Capella
, Rigel
, Procyon
, Achernar and Betelgeuse
—Achernar is the hottest and bluest. It lies at the southern tip of the constellation.
Achernar is a bright, blue, B3-type star of six to eight solar mass
es lying approximately 144 ly away. Although classified as a main-sequence (dwarf) star, it is about 3,000 times more luminous than the Sun
. Achernar is in the deep southern sky and never rises above 33°N, roughly the latitude of Dallas, Texas. Achernar is best seen from the southern hemisphere in November; it is circumpolar
below 33°S.
Until about March 2000, Achernar and Fomalhaut
were the two first-magnitude stars furthest in angular distance from any other first-magnitude star in the celestial sphere
. Antares
, in the constellation of Scorpius
, is now the most isolated first-magnitude star, although Antares is located in a constellation with many bright second-magnitude stars, whereas the stars surrounding Achernar and Fomalhaut are considerably fainter.
Achernar is the least spherical
star in the Milky Way studied to date. It spins so rapidly that its equatorial diameter is 56% greater than its polar diameter. Since it is, actually, a binary star, its highly distorted shape may cause non-negligible departures of the companion's trajectory with respect to a Keplerian ellipse. A similar situation occurs for the star Regulus
.
In Chinese
, , meaning Crooked Running Water, refers to an asterism consisting of Achernar, ζ Phoenicis
and η Phoenicis
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....
Eridanus
Eridanus (constellation)
Eridanus is a constellation. It is represented as a river; its name is the Ancient Greek name for the Po River. It was one of the 48 constellations listed by the 2nd century astronomer Ptolemy, and it remains one of the 88 modern constellations. It is the sixth largest of the modern...
and the ninth-brightest star in the night sky. Of the top ten apparent brightest stars (excluding our Sun)—Sirius
Sirius
Sirius is the brightest star in the night sky. With a visual apparent magnitude of −1.46, it is almost twice as bright as Canopus, the next brightest star. The name "Sirius" is derived from the Ancient Greek: Seirios . The star has the Bayer designation Alpha Canis Majoris...
, Canopus
Canopus
Canopus |Alpha]] Carinae) is the brightest star in the southern constellation of Carina and Argo Navis, and the second brightest star in the night-time sky, after Sirius. Canopus's visual magnitude is −0.72, and it has an absolute magnitude of −5.53.Canopus is a supergiant of spectral...
, Alpha Centauri
Alpha Centauri
Alpha Centauri is the brightest star in the southern constellation of Centaurus...
, Arcturus, Vega
Vega
Vega is the brightest star in the constellation Lyra, the fifth brightest star in the night sky and the second brightest star in the northern celestial hemisphere, after Arcturus...
, 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...
, Rigel
Rigel
Rigel is the brightest star in the constellation Orion and the sixth brightest star in the sky, with visual magnitude 0.18...
, Procyon
Procyon
Procyon is the brightest star in the constellation Canis Minor. To the naked eye, it appears to be a single star, the seventh brightest in the night sky with a visual apparent magnitude of 0.34...
, Achernar and Betelgeuse
Betelgeuse
Betelgeuse, also known by its Bayer designation Alpha Orionis , is the eighth brightest star in the night sky and second brightest star in the constellation of Orion, outshining its neighbour Rigel only rarely...
—Achernar is the hottest and bluest. It lies at the southern tip of the constellation.
Solar mass
The solar mass , , is a standard unit of mass in astronomy, used to indicate the masses of other stars and galaxies...
es lying approximately 144 ly away. Although classified as a main-sequence (dwarf) star, it is about 3,000 times more luminous than 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...
. Achernar is in the deep southern sky and never rises above 33°N, roughly the latitude of Dallas, Texas. Achernar is best seen from the southern hemisphere in November; it is circumpolar
Circumpolar star
A circumpolar star is a star that, as viewed from a given latitude on Earth, never sets , due to its proximity to one of the celestial poles...
below 33°S.
Until about March 2000, Achernar and Fomalhaut
Fomalhaut
Fomalhaut is the brightest star in the constellation Piscis Austrinus and one of the brightest stars in the sky. Fomalhaut can be seen low in the southern sky in the northern hemisphere in fall and early winter evenings. Near latitude 50˚N, it sets around the time Sirius rises, and does not...
were the two first-magnitude stars furthest in angular distance from any other first-magnitude star in the celestial sphere
Celestial sphere
In astronomy and navigation, the celestial sphere is an imaginary sphere of arbitrarily large radius, concentric with the Earth and rotating upon the same axis. All objects in the sky can be thought of as projected upon the celestial sphere. Projected upward from Earth's equator and poles are the...
. Antares
Antares
Antares is a red supergiant star in the Milky Way galaxy and the sixteenth brightest star in the nighttime sky . Along with Aldebaran, Spica, and Regulus it is one of the four brightest stars near the ecliptic...
, in the constellation of 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...
, is now the most isolated first-magnitude star, although Antares is located in a constellation with many bright second-magnitude stars, whereas the stars surrounding Achernar and Fomalhaut are considerably fainter.
Achernar is the least spherical
Sphere
A sphere is a perfectly round geometrical object in three-dimensional space, such as the shape of a round ball. Like a circle in two dimensions, a perfect sphere is completely symmetrical around its center, with all points on the surface lying the same distance r from the center point...
star in the Milky Way studied to date. It spins so rapidly that its equatorial diameter is 56% greater than its polar diameter. Since it is, actually, a binary star, its highly distorted shape may cause non-negligible departures of the companion's trajectory with respect to a Keplerian ellipse. A similar situation occurs for the star 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...
.
Name
The name originally comes from the Arabic , meaning, "The End of the River" or "River's End".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 Crooked Running Water, refers to an asterism consisting of Achernar, ζ Phoenicis
Zeta Phoenicis
Zeta Phoenicis is a 280 light-year distant star in the constellation Phoenix. It is an Algol-type eclipsing binary star and its apparent magnitude fluctuates between 3.9 and 4.4 with a period of 1.66977 days...
and η Phoenicis
Fiction
- Achernar in fiction