Antares is the bright red star at the heart of the constellation Scorpius. It is a red supergiant about 550 light-years away and roughly 700 times wider than the Sun. Its name means “rival of Mars” because its colour matches the red planet. It is best seen on summer evenings from the Northern Hemisphere and is high overhead from the Southern Hemisphere.
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Antares at a glance
| Other names | Alpha Scorpii, Jyeshtha (India) |
|---|---|
| Constellation | Scorpius (the Scorpion) |
| Brightness | About magnitude +1.0, varies between about 0.6 and 1.6 |
| Distance | About 550 light-years |
| Type | Red supergiant (M1.5Iab) |
| Mass | Roughly 12–15 Suns |
| Size | About 700 times the Sun’s diameter |
| Temperature | About 3,600 K |
| Companion | Antares B, a hot blue-white star, magnitude 5.5 |
| Best time to see it | Evenings around July (highest at about 9 p.m.) |
| Where on Earth | Visible from everywhere south of about 64°N |
The rival of Mars
The name Antares comes from Greek and is usually translated as “rival of Mars” or “anti-Ares” (Ares being the Greek name for Mars). The star’s deep orange-red colour looks so much like the planet that the two are easy to confuse, especially when Mars passes nearby, which happens every two years or so because Antares lies close to the ecliptic, the path of the planets.
A supergiant star
Like Betelgeuse, Antares is a red supergiant in the final stages of its life. It is roughly 12 to 15 times as massive as the Sun and so swollen that, placed at the centre of the Solar System, its surface would reach beyond the orbit of Mars. Its outer layers are cool, about 3,600 K, which is why it glows red. Antares is expected to end its life as a supernova, probably within the next million years, but there is no sign that this is imminent. In 2017 astronomers used the ALMA and VLA radio telescopes to map the turbulent atmosphere of Antares in detail, the most detailed map ever made of a star other than the Sun at that time.
Antares B: the hidden blue companion
Antares has a hot, blue-white companion, Antares B, about 3 arcseconds away. Because it sits so close to the glaring red supergiant it is a difficult target, but in a telescope with very steady air the contrast between the red and greenish-blue stars is striking. The companion is also seen briefly during lunar occultations, when the Moon passes in front of Antares; for a few seconds the companion disappears or reappears separately.
How to see Antares
Antares is the bright red star in the body of Scorpius, one of the few constellations that really looks like its name, with a curved tail ending in a sting. From the Northern Hemisphere it is a summer star, low in the south on evenings from June to August; it never climbs high from Europe or the northern United States, and it does not rise at all north of about 63°N. From India and the tropics it is well placed, and from the Southern Hemisphere Scorpius passes overhead on winter evenings, set against the brightest part of the Milky Way.
In November Antares is close to the Sun and lost in its glare; it returns in the morning sky in December and January. Look for it with the Moon, which passes close to it every month.
In other cultures
In Indian astronomy Antares marks the nakshatra Jyeshtha (“the eldest”). Many cultures saw it as a heart or a burning coal; to Polynesian navigators the stars of Scorpius formed a great fish hook.
Binocular treasures next to Antares
Antares sits in one of the richest parts of the sky. Just over a degree to its west is M4, one of the closest globular star clusters to Earth, a ball of tens of thousands of ancient stars about 7,000 light-years away, visible in binoculars as a soft glow. Antares also lights up colourful clouds of gas and dust in the nearby Rho Ophiuchi region, which appear yellow and orange in long-exposure photographs. A little farther east, the star clouds of Sagittarius mark the direction of the centre of the Milky Way.
When Mars passes near Antares, as it does roughly every two years, the two make a striking pair of red points of light, and it is easy to see why ancient observers thought of them as rivals.
Frequently asked questions about Antares
Why is Antares red?
Antares is a red supergiant with a cool surface of about 3,600 K, so it gives out mostly red and orange light.
How big is Antares?
About 700 times wider than the Sun. At the Sun’s position it would extend past the orbit of Mars.
How far away is Antares?
About 550 light-years.
Will Antares explode?
Yes, eventually. As a massive red supergiant it should end as a supernova, probably within a million years, but nothing suggests it will happen soon.
When can I see Antares?
On summer evenings in the Northern Hemisphere (June–August, low in the south) and on winter evenings in the Southern Hemisphere, where it passes high overhead.
Sources: Antares overview and references. Star data from standard catalogues; positions and rise/set times are calculated by SpaceTracker.live with the Astronomy Engine library.