Ruby red Antares is the Scorpion’s Heart
Antares is an eye-catching star, shining with a distinctive bright red sparkle on northern summer evenings. In the Southern Hemisphere, it’s a red beacon in winter evening skies. This star, also known as Alpha Scorpii, lies about 550 light-years away. It’s the brightest star in the zodiacal constellation Scorpius the Scorpion, which has figured prominently in the sky lore of ancient cultures. Antares is often called the Scorpion’s Heart.
Today, we know that Antares is a very large massive star – a red supergiant – in the final stages of its life.
Antares as a red supergiant
It’s classified as an M1 red supergiant star.
The M1 designation means that Antares is reddish in color and much cooler than many other stars. Its surface temperature is about 6,100 degrees F (3,400 degrees C). That’s in contrast to our sun’s surface temperature of about 10,000 degrees F (5,800 degrees C).
So Antares is relatively cool, and its surface temperature is relatively low. Yet the star appears very bright to us. That’s because Antares is a truly enormous star. Its surface area – the surface from which light can escape this star – is gigantic. If you could hold our sun and Antares side by side, you’d find Antares more than 11,000 times brighter than our sun, and with 680 times the diameter!
And that’s just in visible light. When you consider all the various wavelengths of electromagnetic radiation, Antares pumps out about 75,900 times the energy of our sun!
Like all M-type giants and supergiants, Antares is close to the end of its lifetime. Someday soon (astronomically speaking), it will effectively run out of fuel and collapse. The resulting infall of its enormous mass – some 11-14 times the mass of our sun – will cause an immense supernova explosion, ultimately leaving a tiny neutron star or possibly a black hole. This explosion, which could be tomorrow or millions of years from now, will be spectacular as seen from Earth, but we are far enough away that there likely is no danger to our planet.
And the meantime, astronomers love to explore huge Antares. In 2017, the European Southern Observatory released a detailed image, taken in infrared wavelengths, of features on Antares’ surface. The also found that there was a lot of turbulence in the star’s atmosphere and that gases were being expelled further away from the star than expected.
Just how large is Antares?
At 680 times the sun’s radius, Antares is a truly enormous star. That’s more than 3 astronomical units (AU). One AU is the Earth’s average distance from the sun. If by some bit of magic Antares was suddenly substituted for our sun, its surface would extend well past the orbit of Mars!
Recently, astronomers discovered more details about Antares’ outer surface. In 2020, a study of data taken by radio telescopes showed that Antares’s chromosphere (that’s the layer above the star’s surface) extended out by 2.5 times the star’s radius, far more than previously thought. In comparison, our sun’s chromosphere is only 1/200th of its radius.
They also saw that some of the gaseous material ejected by Antares was being lit up by its companion star, Antares B.
Antares and Antares B
Antares isn’t alone. It has a companion, called Antares B. As the image below shows, Antares B is hard to see next to its much brighter companion.
The companion is a blue-white main sequence star with a visual magnitude of just 5.5. This near the edge of what you can see with the unaided eye. Antares itself varies in brightness, and its visual magnitude ranges from 0.6 to 1.6. Antares B is a big star, too, bigger than our sun. It’s about 7 times the sun’s mass and 5 times the sun’s size. But Antares B is no match for the size of mighty Antares.
Antares in history and skylore
Both the Arabic and Latin names for the star Antares mean heart of the Scorpion. If you see this constellation in the sky, you’ll find that Antares does indeed seem to reside at the Scorpion’s heart.
Antares is Greek for rival of Ares, meaning rival of Mars. Antares is sometimes said to be the “anti-Mars.” All this rivalry, as told in ancient celestial lore, stems from the colors of Mars and Antares. Both are red in color, and, for a few months every couple of years Mars is much brighter than Antares. Most of the time, though, Mars is near the same brightness or much fainter than Antares. Every couple of years, Mars passes near Antares, which was perhaps seen as taunting the star, as Mars moves rapidly through the heavens and Antares, like all stars, seems fixed to the starry firmament.
As is typical, more mythology attends the full constellation of Scorpius than the star Antares. Perhaps the most well known story of Scorpius is that the Earth goddess, Gaia, sent him to sting arrogant Orion, who had claimed his intent to kill all animals on the planet. Scorpius killed Orion, and both were placed in the sky, although in opposite sides of the heavens, positioned as if to show the Scorpion chasing the Mighty Hunter.
In Polynesia, Scorpius is often seen as a fishhook, with some stories describing it as the magic fishhook used by the demigod Maui to pull up land from the ocean floor that became the Hawaiian islands. According to the University of Hawaii’s Institute for Astronomy, the Hawaiian name for Antares, Lehua-kona, seems to have little to do with the constellation. It means “southern lehua blossom.”
How to see Antares
If you look southward in early evening from late spring to early fall, you’re likely to notice the fishhook pattern of Scorpius the Scorpion, with ruby Antares at its heart. If you think you’ve found Antares, aim binoculars in its direction. With the eye alone, and with binoculars, you should notice its reddish color. If you have binoculars and a dark sky, also scan just to the right of Antares. You should see a little star cluster, M4.
Antares is the 16th brightest star in the sky. It’s located in the southern half of Earth’s sky and is a beautiful sight from both the Northern and Southern Hemispheres. From our northerly latitudes, we see it arc across the south. Because we’re sometimes looking at it through a greater thickness of Earth’s atmosphere in the direction toward the horizon, we see Antares twinkle fiercely.
From the Southern Hemisphere, Antares appears higher in the sky. Your chance of seeing this star on any given night increases as you go farther southward on Earth’s globe. If you traveled to about 67° south latitude, you’d find that Antares is circumpolar. That means that, from Earth’s southernmost regions, Antares never sets and is visible every night of the year.
From most of the Northern Hemisphere, short of the Arctic, Antares is within view. Well, not quite the Arctic, but anywhere south of 63° north latitude can – at one time or another – see Antares. (Helsinki, yes, Fairbanks, no)
The midnight culmination of Antares is on or near June 1. That’s when Antares is highest in the sky at midnight (midway between sunset and sunrise). It is highest in the sky at about dawn in early March and at about sunset in early September.
Antares’ position is RA:16h 29m 24s, dec: -26° 25′ 55″.
Bottom line: Antares is a brilliant ruby red star in summer for the Northern Hemisphere (winter for the Southern Hemisphere). It’s an enormous red supergiant star, whose constellation – Scorpius the Scorpion – has a rich history in skylore.