Omicron Scorpii (ο Sco, ο Scorpii) is a

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

zodiac The zodiac is a belt-shaped region of the sky that extends approximately 8° north or south (as measured in celestial latitude) of the ecliptic, the Sun path, apparent path of the Sun across the celestial sphere over the course of the year. ...

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 Scorpius. With an apparent visual magnitude of +4.57, it is visible to the naked eye.

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 indicate a distance 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 located in the proximity of the Rho Ophiuchi dark cloud. This is a white A-type

bright giant A giant star is a star with substantially larger radius and luminosity than a main-sequence (or ''dwarf'') star of the same surface temperature.Giant star, entry in ''Astronomy Encyclopedia'', ed. Patrick Moore, New York: Oxford University Press ...

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 A4II/III. It is one of the brighter members of this rare class of stars, making it of interest for study. Omicron Scorpii has about eight times the mass of the Sun, fifteen times the radius, and is roughly 40 million years old. The star is radiating around 3,200 times the luminosity of the Sun from its outer atmosphere 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 about 8,128 K. It does not display an infrared excess due to circumstellar dust or a possible infrared-bright companion, but the light from this star is subject to

extinction Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...

from interstellar dust. This star was originally designated by Lacaille as o Scorpii (lowercase Latin o) instead of omicron, but this designation was reinterpreted as Omicron Scorpii when the star originally designated by Bayer as Omicron Scorpii was reassigned to Libra as

Upsilon Librae Upsilon Librae (υ Lib, υ Librae) is the Bayer designation for a double star in the zodiac constellation Libra. With an apparent visual magnitude of 3.628, it is visible to the naked eye. The distance to this star, based upon an annual pa ...

. Omicron Scorpii was occasionally mentioned as a possible member of the Upper Scorpius sub-group in the Scorpius–Centaurus

OB association In astronomy, stellar kinematics is the observational study or measurement of the kinematics or motions of stars through space. Stellar kinematics encompasses the measurement of stellar velocities in the Milky Way and its satellites as well as t ...

during the 20th century. However, it does not appear in more recent membership lists for this group due to its small proper motion and small trigonometric parallax as measured by

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 ...

. This suggests that it is a background star unrelated to Scorpius–Centaurus.

References

{{Stars of Scorpius, state=collapsed A-type bright giants Upper Scorpius Scorpius Scorpii, Omicron Scorpii, 19 147084 080079 6081 Durchmusterung objects