Eta Herculis (η Her, η Herculis) is a third-magnitude

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

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 ...

Hercules Hercules (, ) is the Roman equivalent of the Greek divine hero Heracles, son of Jupiter and the mortal Alcmena. In classical mythology, Hercules is famous for his strength and for his numerous far-ranging adventures. The Romans adapted the Gr ...

. It is located at 110 light-years from Earth.

Properties

Eta Herculis is a G-type

giant star A giant star has a substantially larger radius and luminosity than a main-sequence (or ''dwarf'') star of the same surface temperature. They lie above the main sequence (luminosity class V in the Yerkes spectral classification) on the Hertzsp ...

. With a

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 ...

G7.5IIIb, it is considerably larger and more evolved than 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 ...

, having a mass that is two times solar and a radius 8.9

times Time is the continued sequence of existence and events, and a fundamental quantity of measuring systems. Time or times may also refer to: Temporal measurement * Time in physics, defined by its measurement * Time standard, civil time specificat ...

. Though it only shines with an

apparent magnitude Apparent magnitude () is a measure of the Irradiance, 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 (astronomy), ...

of 3.48, it is part of the "Keystone" asterism, visible overhead in the mid-summer night sky to

northern Northern may refer to the following: Geography * North North is one of the four compass points or cardinal directions. It is the opposite of south and is perpendicular to east and west. ''North'' is a noun, adjective, or adverb indicating ...

observers, allowing it to be easily recognized. Eta Herculis is 46 times more luminous than the Sun. 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 and distances of ...

satellite A satellite or an artificial satellite is an object, typically a spacecraft, placed into orbit around a celestial body. They have a variety of uses, including communication relay, weather forecasting, navigation ( GPS), broadcasting, scient ...

mission estimated its distance at roughly 34.4

parsec The parsec (symbol: pc) is a unit of length used to measure the large distances to astronomical objects outside the Solar System, approximately equal to or (AU), i.e. . The parsec unit is obtained by the use of parallax and trigonometry, and ...

s from Earth, or 112

light year A light-year, alternatively spelled light year (ly or lyr), is a unit of length used to express astronomical distance, astronomical distances and is equal to exactly , which is approximately 9.46 trillion km or 5.88 trillion mi. As defined by t ...

s away. If one follows the line connecting Eta Herculis with

Zeta Herculis Zeta Herculis, Latinized from ζ Herculis, is a multiple star system in the constellation Hercules. It has a combined apparent visual magnitude of 2.81, which is readily visible to the naked eye. Parallax measurements put it at a distan ...

one comes across one of the earliest and most stunning

globular clusters A globular cluster is a spheroidal conglomeration of stars that is bound together by gravity, with a higher concentration of stars towards its center. It can contain anywhere from tens of thousands to many millions of member stars, all orbiting ...

in the nighttime sky, M13, discovered in 1714 by

Edmond Halley Edmond (or Edmund) Halley (; – ) was an English astronomer, mathematician and physicist. He was the second Astronomer Royal in Britain, succeeding John Flamsteed in 1720. From an observatory he constructed on Saint Helena in 1676–77, Hal ...

. Eta Herculis is a

double star In observational astronomy, a double star or visual double is a pair of stars that appear close to each other as viewed from Earth, especially with the aid of optical telescopes. This occurs because the pair either forms a binary star (i.e. a ...

once thought to be part of a binary

star system A star system or stellar system is a small number of stars that orbit each other, bound by gravity, gravitational attraction. It may sometimes be used to refer to a single star. A large group of stars bound by gravitation is generally calle ...

References

External links

*Jim Kaler's Star
Eta Herculis
{{DEFAULTSORT:Eta Herculis Hercules (constellation) Herculis, Eta Double stars Triple star systems G-type giants Herculis, 044 081833 150997 6220 BD-39 3029