Meet Shaula: The Scorpion’s Triple-Pronged Stinger

The Vitals (for Shaula A)

Official name	Shaula
Other designations	Lambda Scorpii, HIP 85927, HD 158926, HR 6527
Nicknames	-
Apparent magnitude	1.63
Distance from Earth	571 light-years*
Type	B2 subgiant star
Color	Blue
Mass	10 solar masses
Radius	6 solar radii
Constellation	Scorpius
Right ascension	17h 33m 36s
Declination	-37° 06' 13"
Multiple system?	Yes
Variable star?	Yes
Exoplanets status	None known
Probable fate	Supernova

Physical Characteristics

Shaula, a bright blue star in the constellation Scorpius, is actually a triple-star system. When viewed without any optical aid, Shaula looks just like a point of light, no different from any other star. You certainly can’t split the three individual stars with your own eyes the way you can, say, Mizar and Alcor. And yet if you look at Shaula with a telescope — even a huge telescope…it still looks like a single point of light. What’s going on?

The three stars are so close together, and such a long distance from Earth, that from our perspective their light simply blurs together into one. So how do we even know there are three of them? Because when Shaula is examined with a spectroscope, we can see the stars’ regular motions relative to each other by the red- and blueshifts of specific wavelengths in their spectra. So even though we can’t visually split the light into three separate bodies, the stars’ orbital patterns are clearly discernable in the spectroscopic data.

The largest of the three stars, called Shaula A, is a hot, blue star that’s also slightly variable,  dimming and brightening by less than a tenth of a magnitude in a regular rhythm. A second star, Shaula B, is very similar to Shaula A, though a bit smaller. The two of them orbit each other at a distance of, on average, about 5.7 astronomical units. That’s just a bit more than Jupiter’s distance from the Sun, but unlike Jupiter’s almost-circular orbit, the two stars have oval-shaped orbits that take them as far away from each other as 7 astronomical units.

The two stars sprint around each other at a tremendous rate, completing a joint circuit around their common center of gravity in three years. You may recall that Jupiter’s orbital period around the Sun is about 12 years. The Shaula star’s mutual orbit is so much faster because the two stars have far more combined mass than the Sun and Earth do.

The third member of the stellar group is Shaula Ab, a smaller star (though still nearly twice the Sun’s mass) that orbits Shaula A at very close range — screaming along its orbit in just 6 days. Shaula Ab might be a white dwarf similar to “the Pup” (Sirius B), but more likely it’s a protostar that hasn’t yet moved onto the main sequence of hydrogen fusion.   

Origin / Mythology

In modern constellation lore, the stars of Scorpius are depicted specifically as the scorpion from Greek myth, dispatched by Artemis to combat boastful Orion. Zeus eventually intervenes and prevents future trouble by keeping Scorpius and Orion on opposite sides of the sky, so that they don’t share the same season.

But the concept of these stars representing a scorpion goes beyond Greece. We know that Shaula in particular is supposed to be the creature’s tail, as “Al-shawlah” was the star’s name in Arabic, meaning “the stinger” or “the raised tail” — giving us a clear indication of how Scorpius is intended to be viewed.

Even cultures seemingly far removed from the Greek/Arabic traditions sometimes shared the scorpion concept. Aztec astronomers called the area around Scorpius “Citlalcolotl” for “the scorpion star.” Mayan stargazers also maintained the image of a scorpion near Antares, although Shaula itself was broken off into the nearby constellation of a rattlesnake.

Traditional Hawaiian stargazers took the same basic shape of the scorpion but used the curving tail to imagine a fishhook; in this instance Shaula serves as the point at the end of the hook. The hero Maui pulls the Hawaiian Islands out of the sea using Shaula and its nearby stars.

Further southwest towards Australia, the astronomers of Vanuatu used Shaula and a couple of other stars to form a rat, whose wanderings near the zenith in spring indicated crop-planting season.

How to See Shaula

This one makes a nice observational challenge for much of the U.S. Scorpius is a fairly southern constellation, so seeing it well requires good timing. Late spring through early summer is the optimal viewing season, although it’s possible to see this star at other times if you try hard enough.

Scorpius is always low in the southern sky when viewed from the U.S., but it’s a big constellation, with brilliant Antares gliding along the top — making that star fairly easy to find. But Shaula, down in the Scorpion’s tail, is much lower in the sky. In the northern U.S., you may well have to stay up until midnight or beyond before Shaula rises high enough to clear the haze along the horizon or obstructions like buildings. Once reaching its peak height (and not too high at that), Shaula immediately plunges again below the horizon before the night is over. But the situation improves rapidly the farther south you travel. For more southern viewers, Shaula rises earlier, climbs higher, and lingers longer throughout the night. 

To find Shaula, try to locate bright red Antares first. The body of the Scorpion is pretty distinct — especially the curving tail — so you can use these stars as stepping stones to Shaula if the constellation is high enough in the sky. But if the tail is partially obscured, you can instead jump from red Antares straight down to blue Shaula. Because it’s the second-brightest star in Scorpius, it’s pretty obvious. Shaula is paired nicely with nearby Lesath (though not as a system); it’s the only pair of decently bright stars in the vicinity, making their identification easier.