Antares
Antares is the brightest star in the constellation of Scorpius. It has the Bayer designation α Scorpii, which is Latinised to Alpha Scorpii. Often referred to as "the heart of the scorpion", Antares is flanked by σ Scorpii and τ Scorpii near the center of the constellation. Distinctly reddish when viewed with the naked eye, Antares is a slow irregular variable star that ranges in brightness from an apparent visual magnitude of +0.6 down to +1.6. It is on average the fifteenth-brightest star in the night sky. Antares is the brightest and most evolved stellar member of the Scorpius–Centaurus association, the nearest OB association to the Sun. It is located about 170 parsecs (550 ly) from Earth at the rim of the Upper Scorpius subgroup, and is illuminating the Rho Ophiuchi cloud complex in its foreground.
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Scorpius |
| Pronunciation | /ænˈtɛəriːz/ an-TAIR-eez), |
| Right ascension | 16h 29m 24.45970s |
| Declination | −26° 25′ 55.2094″ |
| Apparent magnitude (V) | 0.6–1.6 + 5.5 |
| Characteristics | |
| Evolutionary stage | Red supergiant |
| Spectral type | M1.5Iab-Ib + B2.5V |
| U−B color index | +1.34 |
| B−V color index | +1.83 |
| Variable type | Lc |
| Astrometry | |
| Radial velocity (Rv) | −3.4 km/s |
| Proper motion (μ) | RA: −12.11 mas/yr Dec.: −23.30 mas/yr |
| Parallax (π) | 5.89 ± 1.00 mas |
| Distance | approx. 550 ly (approx. 170 pc) |
| Absolute magnitude (MV) | −5.28 (variable) |
| Details | |
| A | |
| Mass | 11–16 M☉ |
| Radius | 680 (varies by 19%) R☉ |
| Luminosity | 75900+53000 −31200 L☉ |
| Surface gravity (log g) | −0.1 to −0.2 cgs |
| Temperature | 3,660±120 K |
| Rotational velocity (v sin i) | 20 km/s |
| Age | 15±5 Myr |
| B | |
| Mass | 7.2 M☉ |
| Radius | 5.2 R☉ |
| Luminosity | 2,754 L☉ |
| Surface gravity (log g) | 3.9 cgs |
| Temperature | 18,500 K |
| Rotational velocity (v sin i) | 250 km/s |
| Other designations | |
| A: HD 148478, AAVSO 1623-26 | |
| B: HD 148479 | |
| Database references | |
| SIMBAD | Antares |
| α Scorpii A | |
| α Scorpii B | |
Classified as spectral type M1.5Iab-Ib, Antares is a red supergiant, a large evolved massive star and one of the largest stars visible to the naked eye. Its exact size remains uncertain, but if placed at the center of the Solar System, it would extend out to somewhere between the orbits of Mars and Jupiter. Its mass is calculated to be around 12 times that of the Sun. Antares appears as a single star when viewed with the naked eye, but it is actually a binary star system, with its two components called α Scorpii A and α Scorpii B. The brighter of the pair is the red supergiant, while the fainter is a hot main sequence star of magnitude 5.5. They have a projected separation of about 79.1 Tm (529 AU).
Its traditional name Antares derives from the Ancient Greek Ἀντάρης, meaning "rival to Ares", due to the similarity of its reddish hue to the appearance of the planet Mars.