Eta Aquarii is a

star A star is a luminous spheroid of plasma (physics), plasma held together by Self-gravitation, self-gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night sk ...

in the equatorial

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 first constellati ...

of Aquarius. Its identifier is a

Bayer designation A Bayer designation is a stellar designation in which a specific star is identified by a Greek alphabet, Greek or Latin letter followed by the genitive case, genitive form of its parent constellation's Latin name. The original list of Bayer design ...

that is Latinized from η Aquarii, and abbreviated Eta Aqr or η Aqr, respectively. The star is visible to the

naked eye Naked eye, also called bare eye or unaided eye, is the practice of engaging in visual perception unaided by a magnification, magnifying, Optical telescope#Light-gathering power, light-collecting optical instrument, such as a telescope or microsc ...

with an

apparent visual magnitude Apparent magnitude () is a measure of the brightness of a star, astronomical object or other celestial objects like artificial satellites. Its value depends on its intrinsic luminosity, its distance, and any extinction of the object's light ca ...

of 4.04. The distance to this star, as determined by

parallax Parallax is a displacement or difference in the apparent position of an object viewed along two different sightline, lines of sight and is measured by the angle or half-angle of inclination between those two lines. Due to perspective (graphica ...

measurements, is about . It is drifting closer to the

Sun The Sun is the star at the centre of the Solar System. It is a massive, nearly perfect sphere of hot plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy from its surface mainly as visible light a ...

with a

radial velocity The radial velocity or line-of-sight velocity of a target with respect to an observer is the rate of change of the vector displacement between the two points. It is formulated as the vector projection of the target-observer relative velocity ...

of –8 km/s. Eta Aquarii is near the radiant of a meteor shower named after it. The

stellar classification In astronomy, stellar classification is the classification of stars based on their stellar spectrum, spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a Prism (optics), prism or diffraction gratin ...

of Eta Aquarii is B9IV-Vn, which may indicate that it is beginning to evolve away from the

main sequence In astronomy, the main sequence is a classification of stars which appear on plots of stellar color index, color versus absolute magnitude, brightness as a continuous and distinctive band. Stars on this band are known as main-sequence stars or d ...

into a

subgiant A subgiant is a star that is brighter than a normal main-sequence star of the same spectral class, but not as bright as giant stars. The term subgiant is applied both to a particular spectral luminosity class and to a stage in the evolution ...

as the supply of hydrogen at its core becomes exhausted. It is 65 million years old and is spinning rapidly with a high

projected rotational velocity Stellar rotation is the angular motion of a star about its axis. The rate of rotation can be measured from the spectrum of the star, or by timing the movements of active features on the surface. The rotation of a star produces an equatorial bu ...

of 271 km/s. This rotation is causing an equatorial bulge, giving the star an oblate figure with a 24% larger radius at the equator than at the poles. The

Doppler effect The Doppler effect (also Doppler shift) is the change in the frequency of a wave in relation to an observer who is moving relative to the source of the wave. The ''Doppler effect'' is named after the physicist Christian Doppler, who described ...

from the rapid rotation is causing the

absorption line Absorption spectroscopy is spectroscopy that involves techniques that measure the absorption (electromagnetic radiation), absorption of electromagnetic radiation, as a function of frequency or wavelength, due to its interaction with a sample. Th ...

s in the star's

spectrum A spectrum (: spectra or spectrums) is a set of related ideas, objects, or properties whose features overlap such that they blend to form a continuum. The word ''spectrum'' was first used scientifically in optics to describe the rainbow of co ...

to blur, as indicated by the 'n' suffix in the star's classification. Eta Aquarii has an estimated 2.96 times the

mass of the Sun The solar mass () is a frequently used unit of mass in astronomy, equal to approximately . It is approximately equal to the mass of the Sun. It is often used to indicate the masses of other stars, as well as stellar clusters, nebulae, galaxies a ...

and 2.8 times the

Sun's radius Solar radius is a unit of distance used to express the size of objects in astronomy relative to the Sun. The solar radius is usually defined as the radius to the layer in the Sun's photosphere where the optical depth equals 2/3: 1\,R_ = 6.957\ti ...

. The star is radiating 103 times the

luminosity of the Sun The solar luminosity () is a unit of radiant flux ( power emitted in the form of photons) conventionally used by astronomers to measure the luminosity of stars, galaxies and other celestial objects in terms of the output of the Sun. One nominal s ...

from its

photosphere The photosphere is a star's outer shell from which light is radiated. It extends into a star's surface until the plasma becomes opaque, equivalent to an optical depth of approximately , or equivalently, a depth from which 50% of light will esc ...

at an

effective temperature The effective temperature of a body such as a star or planet is the temperature of a black body that would emit the same total amount of electromagnetic radiation. Effective temperature is often used as an estimate of a body's surface temperature ...

of 11,042 K.

Naming

This star, along with γ Aqr (Sadachbia), π Aqr (Seat) and ζ Aqr (Sadaltager / Achr al Achbiya), were ''al Aḣbiyah'' (الأخبية), the Tent. In Chinese, (), meaning ''

Tomb A tomb ( ''tumbos'') or sepulchre () is a repository for the remains of the dead. It is generally any structurally enclosed interment space or burial chamber, of varying sizes. Placing a corpse into a tomb can be called '' immurement'', alth ...

'', refers to an asterism consisting of η Aquarii, γ Aquarii, ζ Aquarii, π Aquarii. Consequently, the

Chinese name Chinese may refer to: * Something related to China * Chinese people, people identified with China, through nationality, citizenship, and/or ethnicity **Han Chinese, East Asian ethnic group native to China. **'' Zhonghua minzu'', the supra-ethni ...

for η Aquarii itself is (, .)AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 5 月 16 日

References

External links

Image Eta Aquarii
{{DEFAULTSORT:Eta Aquarii B-type main-sequence stars B-type subgiants Aquarius (constellation) Aquarii, Eta 8597 BD-00 4384 Aquarii, 062 213998 111497