There are several constellations in our northern sky that have similar counterparts in the southern sky.
In our current evening sky, for instance, is the zodiacal constellation Pisces, composed of two fish tied together on a string or ribbon by their tails. One fish is composed of a faint circle of stars popularly known as the Circlet. "Pisces"' is the Latin word for "fishes"; the singular form is "piscis," and there is indeed a Southern Fish constellation, known as Piscis Austrinus. Using the Great Square of Pegasus, if you imagine a line drawn through the two stars on the right side of the Square (Markab and Scheat, also called Alpha Pegasi and Beta Pegasi) and go straight south, you'll arrive at Fomalhaut, the brightest star in Piscis Austrinus and the 18th brightest star in the sky.
Another pair of counterparts are the Northern Crown (Corona Borealis) and the Southern Crown (Corona Australis). Both are roughly circular, and both are ancient star patterns, dating back to the time of the second-century astronomer Claudius Ptolemy or even earlier, perhaps to Hipparchus almost three centuries before. These crown constellations have also been called wreaths, indicating the very ancient type of distinctive head decoration made of beech, willow or laurel leaves and, in later times, copied from such in precious metal in what we now know as a crown.
The Northern Crown
Corona Borealis is said to represent the crown given to Ariadne, daughter of Minos, the king of Crete, by Dionysus, the ancient Greek god of wine and a very bucolic character who would have considered a nicely intertwined wreath of vines a sufficient tribute. Ariadne, however, was reluctant to accept a marriage proposal from Dionysus (who was in mortal form), since she did not wish to marry a mortal after being deserted by Theseus, the mythical king and founder-hero of Athens.
To prove he was a god, Dionysus (or Bacchus, as the Romans called him) took off his crown and threw it into the heavens as a tribute to Ariadne. Satisfied, she married him and, in the process, became immortal herself.
The Southern Crown
In contrast to the bejeweled Corona Borealis, Corona Australis is said to represent a crown or wreath of laurel or olive leaves. According to one story from Greek mythology, the crown belongs to Chiron, the wisest of all the centaurs.
Another story relating to the Southern Crown comes from the Roman poet Ovid's "Metamorphoses." Juno, Roman queen of the gods, discovered that her husband, Jupiter, was the lover of Semele, who was a mere mortal. Posing as Semele's maid, Juno suggested that Semele ask Jupiter to appear before her in all his glory. Jupiter was appalled at such a request yet did not refuse it. When she gazed upon Jupiter in all his glory, Semele was consumed by fire. Somehow, her unborn son was saved; he ultimately became Bacchus, who, in turn, honored his mother posthumously by placing the Southern Crown in the sky.
So we can thank Bacchus (and the ancient Greeks and Romans) for both crowns becoming constellations.
Related: What's the story behind the stars?(opens in new tab)
The "second scoop"
On September evenings, the Northern Crown stands halfway up in the western sky, while the Southern Crown lies close to the southern horizon, below the Teapot of Sagittarius. Both crowns attract almost immediate attention as the eye sweeps across them. Seven stars, one of second magnitude (Gemma, the crown jewel), form the incomplete circle of Corona Borealis; it actually resembles a tiara rather than a crown.
When I gave sky shows at New York's Hayden Planetarium, however, the Northern Crown was something quite different: It was immediately adjacent to the top of the constellation Boötes, which resembles an elongated kite. But for my audiences, I suggested that Boötes was much better envisioned as an ice cream cone with two scoops. "Unfortunately, it appears that the second scoop has completely slipped off the top!" I'd say. And then I would point to Corona Borealis.
The "lemon slice"
Despite its much fainter stars, which suffer from their low altitude for mid-northern observers, Corona Australis is quite attractive because there are so many more stars (11), and the circlet is practically complete. The late George Lovi (1939-1993), who was on the lecture staff of the Hayden Planetarium during the 1980s and early '90s, found a different use for this star pattern. First, he would point out the Teapot asterism of Sagittarius; then he would ask his audience if they would like lemon with their tea. He would then point to a slice of lemon: Corona Australis.
"Do I hear that some of you prefer milk with your tea?" he would say. "The Milky Way flows right past!"
Two odd stars
One of the more remarkable stars in the sky is R Coronae Borealis, popularly known as R Cor Bor. Put simply, it is a nova in reverse. Normally shining at magnitude 5.9, at completely irregular intervals, this star will suddenly fade, sometimes by as much as eight magnitudes (nearly 1,600 times), as dark clouds of carbon material, or "soot clouds," erupt in the star's atmosphere. Its brightness then slowly recovers as the material dissipates. The fall is quite rapid, and the return to normal is much slower, with occasional relapses. The fade-down of the bright red star Betelgeuse in Orion in 2019 likely was caused by a similar cloud of obscuring matter.
And then there is T Coronae Borealis, also known as the Blaze Star, which currently shines at magnitude 10.2, making it 30 times dimmer than the faintest star on the threshold of naked-eye visibility. (Lower magnitudes indicate higher brightness, and vice versa.) But more than 150 years ago, on May 12, 1866, this star suddenly brightened to magnitude 2, becoming nearly as luminous as Polaris (the North Star). Known as a recurrent nova, T Coronae Borealis repeated the performance unexpectedly on the night of Feb. 9, 1946, and sometime in the future, it will probably do so again.
In fact, considering the flare-ups of 1866 and 1946 were separated by almost exactly 80 years, perhaps another flare-up could be just around the corner.
The one that got away
In his autobiography, "Starlight Nights," (Harper and Row, 1965) Leslie C. Peltier (sometimes called "the world's greatest nonprofessional astronomer") wrote that at every opportunity from 1920 on — more than 25 years — he kept a careful watch on T Coronae. But on the once-in-a-lifetime night in 1946 when the star suddenly brightened, Peltier was asleep!
On that cold February morning, the alarm clock rang at 2:30 a.m., but upon awakening, Peltier sneezed a couple of times and thought he might be coming down with a cold, or maybe something worse. "Self-pity comes easy at 2:30 on a cold February morning," he later wrote, "so I went back to my warm bed."
Of course, after Peltier found out that he had missed out on the unexpected flare-up of the star he had been monitoring for more than a quarter of a century, he was not a happy camper.
"I still have the feeling that T [Coronae Borealis] could have shown me more consideration," he wrote. "We had been friends for many years; on thousands of nights, I had watched over it as it slept, and then, it arose in my hour of weakness as I nodded at my post. I am still watching it, but now it is with a wary eye. There is no warmth between us anymore."
Joe Rao serves as an instructor and guest lecturer at New York's Hayden Planetarium (opens in new tab). He writes about astronomy for Natural History magazine (opens in new tab), the Farmers' Almanac (opens in new tab) and other publications. Follow us on Twitter @Spacedotcom (opens in new tab) and on Facebook (opens in new tab).