Sigma Ophiuchi, Latinized from σ Ophiuchi, is a single, orange-hued

star A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked ...

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 origins of the e ...

Ophiuchus. Its apparent visual magnitude is 4.31, which is bright enough to be faintly visible to the naked eye. The annual parallax shift of 3.62

mas Mas, Más or MAS may refer to: Film and TV * Más y Menos, fictional superhero characters, from the Teen Titans animated television series * Más (Breaking Bad), "Más" (''Breaking Bad''), a season three episode of ''Breaking Bad'' Songs * Más ( ...

as seen from Earth provides a distance estimate of roughly 900

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. It is moving closer to the Sun with a

radial velocity The radial velocity or line-of-sight velocity, also known as radial speed or range rate, of a target with respect to an observer is the temporal rate of change, rate of change of the distance or Slant range, range between the two points. It is e ...

of −28 km/s. This is an

evolved Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation t ...

giant star of type K 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 grati ...

of K2 III. Wittkowski et al. (2017) consider it to have a luminosity class of II-III, suggesting it is in a transitional zone between giants and supergiant stars. It has around 5 times the

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

and 73 times the Sun's radius. The star is radiating 2,047 times the Sun's luminosity from its enlarged

photosphere The photosphere is a star's outer shell from which light is radiated. The term itself is derived from Ancient Greek roots, φῶς, φωτός/''phos, photos'' meaning "light" and σφαῖρα/''sphaira'' meaning "sphere", in reference to it ...

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 4,540 K.

References

{{DEFAULTSORT:Sigma Ophiuchi K-type giants Suspected variables Ophiuchi, Sigma Ophiuchus J17263087+0408252 BD+04 3422 Ophiuchi, 49 157999 085355 6498