Science & history · Star guide
Antares, the red heart of Scorpius
Antares is the reddish star at the heart of Scorpius, a red supergiant about 700 times the Sun's diameter. Its name compares it to Mars, and it is easy to see why.
About this picture
NASA/Goddard Space Flight Center Scientific Visualization Studio. Gaia DR2: ESA/Gaia/DPAC. Constellation figures based on those developed for the IAU by Alan MacRobert of Sky and Telescope magazine (Roger Sinnott and Rick Fienberg). NASA's page (opens in a new tab).
The map is a composite of 1.7 billion catalogued stars, not a photograph from one place: it shows stars far too faint for the eye, and no weather, Moon or city light. It is drawn here in this chart's projection, with each star where it was in 2000; the fastest-moving bright star has shifted about a minute of arc since, far less than a pixel here.
How to spot it: The reddish star at the heart of the Scorpion's curve. Source (opens in a new tab)
What you are looking at
Antares is a red supergiant about 700 times wider than the Sun, late in its life.
ESO (opens in a new tab) describes Antares as a huge and comparatively cool red supergiant in the late stages of its life, on the way to becoming a supernova. It now has about 12 times the Sun's mass and about 700 times its diameter; it probably started with about 15 solar masses and has shed some three since.
ESO explains (opens in a new tab) that stars like this form with between nine and 40 times the Sun's mass, and that as a red supergiant the star's atmosphere spreads out until it is large and luminous but thin. To the unaided eye Antares shows a strong red tint at the heart of Scorpius.
Sources for this section ESO, Best Ever Image of a Star's Surface and Atmosphere (eso1726, 2017) (opens in a new tab)
Like Mars
Its Greek name means “like Mars”, for its colour.
The name is Greek and, as Ian Ridpath explains (opens in a new tab), means “like Mars”, for its strong reddish-orange colour. It is often translated “rival of Mars”, but the star-name scholar Paul Kunitzsch pointed out that the Greek word anti can mean “like”.
Its Arabic name, qalb al-'aqrab, means the scorpion's heart (opens in a new tab). Ptolemy, who named very few stars, named this one, describing it in the Almagest as the reddish middle star of three bright ones in the Scorpion's body; oddly, he classed it as second magnitude rather than first.
Sources for this section Ian Ridpath, Star Tales: Scorpius (opens in a new tab)
The best view of a star's surface
In 2017 Antares became the star other than the Sun whose surface we have seen best.
In 2017 a team led by Keiichi Ohnaka used ESO's Very Large Telescope Interferometer, which combines several telescopes into the equivalent of one up to 200 metres across, to make the most detailed image (opens in a new tab) yet of any star but the Sun, and the first map of how gas moves in another star's atmosphere.
They found turbulent, thin gas much further out than predicted (opens in a new tab), moving in ways convection alone cannot explain. How such stars lose mass so quickly late in life has been an open question for over half a century, and the team suggests some new, unknown process may be at work.
Sources for this section ESO, Best Ever Image of a Star's Surface and Atmosphere (eso1726, 2017) (opens in a new tab)
A cluster next door
Just beside Antares in the sky is the nearest globular cluster to Earth.
Close to Antares in the sky lies Messier 4 (opens in a new tab), at about 5,500 light-years the nearest globular cluster to Earth: a ball of more than 100,000 old stars, discovered in 1746 by the Swiss astronomer Jean-Philippe Loys de Chéseaux.
NASA's Hubble team (opens in a new tab) expects it to contain up to 40,000 white dwarfs, the cores of ancient stars, which is why astronomers use clusters like it to estimate the ages of the oldest stars.
How to see it At magnitude 5.9 and right beside Antares, M4 is relatively easy to find with a small telescope (opens in a new tab), where it shows as a soft glow, nothing like Hubble's picture.
Sources for this section NASA Hubble, Messier 4 (opens in a new tab)
Where on Earth, and when
It rises from anywhere south of about 64°N.
South of about 64°S, it never sets.
It climbs at least 20° high, the finder's threshold for a suggestion, from anywhere south of about 44°N.
It is highest in the evening sky, at about 9 p.m. local time, in mid-July, from either hemisphere, wherever it rises. With daylight saving time, that is nearer 10 p.m. on the clock.
Worked out by this site from the Bright Star Catalogue, for a flat, clear horizon. Hills, buildings, haze and city light all cut into this; the air also lifts objects near the horizon by about half a degree. For your own place and night, use the sky finder.
Sources
- Astronomy ESO, Best Ever Image of a Star's Surface and Atmosphere (eso1726, 2017) (opens in a new tab) for its size, mass, history, future and the 2017 surface map · checked 27 September 2026
- History Ian Ridpath, Star Tales: Scorpius (opens in a new tab) for its name and Ptolemy's description · checked 27 September 2026
- Astronomy NASA Hubble, Messier 4 (opens in a new tab) for Messier 4 · checked 27 September 2026
