Eta Eridani (η Eridani, abbreviated Eta Eri, η Eri), officially named Azha (with a silent 'h', possibly ),
is a
giant star 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
Eridanus. Based on
parallax
Parallax is a displacement or difference in the apparent position of an object viewed along two different lines of sight and is measured by the angle or semi-angle of inclination between those two lines. Due to foreshortening, nearby objects ...
measurements taken during the
Hipparcos
''Hipparcos'' was a scientific satellite of the European Space Agency (ESA), launched in 1989 and operated until 1993. It was the first space experiment devoted to precision astrometry, the accurate measurement of the positions of celestial obj ...
mission, it is approximately 137
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 the
Sun.
Nomenclature
''η Eridani'' (
Latinised to ''Eta Eridani'') is the star'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. ...
.
It bore the traditional name ''Azha'', from the old Arab asterism نَعَام أُدْحِيّ ''udḥiyy al-naʽām'' "the ostrich nest" (or "hatching place"), which included Eta Eridani.
The first word, ادحى ''udḥiyy'', was miscopied as ازحى (readable as ''azḥā'') in medieval manuscripts.
[
In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)]Tau8 Eridani
Tau8 Eridani, Latinized from τ8 Eridani, is a binary star system in the constellation Eridanus. It is visible to the naked eye with a combined apparent visual magnitude of 4.65. The distance to this system can be estimated via the ...
and Tau9 Eridani
Tau9 Eridani (τ9 Eri) is a binary star in the constellation Eridanus. It is visible to the naked eye with an apparent visual magnitude of 4.63. The distance to this system can be estimated using the parallax method, which yields a v ...
.[ Consequently, the Chinese name for Eta Eridani itself is (, en, the Sixth Star of Celestial Meadows).][
]
Properties
η Eridani belongs to spectral class K3 and has a giant luminosity class. It is an evolved star that has expanded to tens times the size of the sun and nearly sixty times its luminosity. It is red clump giant, a star slightly more massive than the sun which is currently fusing helium in its core.[ This is a mild barium star, sometimes referred to a "semi-barium" star. Although most barium stars are in binary systems, η Eridani has no known companion.][
η Eridani is a ]high proper motion star
Proper motion is the astrometric measure of the observed changes in the apparent places of stars or other celestial objects in the sky, as seen from the center of mass of the Solar System, compared to the abstract background of the more distan ...
, a relatively close star that is moving across the sky at a high rate compared to most stars.[ It is suspected to be a variable star with a range from magnitude 3.81 to 3.90.][
]
References
{{DEFAULTSORT:Eta Eridani
K-type giants
Horizontal-branch stars
Barium stars
Suspected variables
High-proper-motion stars
Eridanus (constellation)
Eridani, Eta
Azha
Durchmusterung objects
Eridani, 03
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