Pegasus, the winged horse

By Tom Burns - Stargazing

Most people have heard of the winged (pronounced wing-ed by nerdy types like me) horse Pegasus. Right now, its namesake constellation sits high in the southeast in the early evening. Look for the Great Square of Pegasus, a large square of stars that forms the body of the horse.

Pegasus is usually connected to the exploits of the Greek hero Perseus, partly because of an old movie called Clash of the Titans and its more recent cinematic counterpart.

Perseus is nearby in the northeastern sky, so the connection between the two is perhaps inevitable.

However, Clash of the Titans notwithstanding, Perseus plays only a minor part in the original Greco-Roman story of how the flying horse got into the sky. The Perseus/Pegasus connection seems to be a later invention that didn’t finally take hold until the Middle Ages in Europe.

Pegasus really belonged to a hero whose adventures are just as great as those of the better-known Perseus. He was Bellerophon, the son of King Glaucus of Corinth.

Perseus did have something to do with the birth of Pegasus. The horse’s sort-of mother was Medusa, the Gorgon with hair made from writhing snakes. She was so hideously ugly that her gaze turned people to stone.

Perseus relieved the world of Medusa by lopping off her head, which he kept in a sack as weapon and keepsake. (What a guy!) In old star maps, Perseus is often depicted holding up the Gorgon’s head.

Out of Medusa’s gory neck sprang forth the winged horse Pegasus. A few drops of the Gorgon’s blood fell into the sea, and Pegasus was born.

From that odd moment of birth arose the horse’s most memorable power, which had nothing to do with flying. The horse’s name comes from the Greek word for “springs” or “waters.” Besides being able to fly, Pegasus had the magical power to create its own water supply by stamping its hoof.

The horse traveled the world, eventually alighting at Mount Helicon, home of the Muses, who were the patron gods of the arts. To their delight, Pegasus stamped his hoof and created a spring of water, which the Muses named Hippocrene, the “Horse’s Fountain.”

Oddly, in some early versions of the old story, Pegasus had no wings at all. He was simply a gorgeous, golden-maned horse of purest white. Also, Pegasus had nothing to do with saving princess Andromeda from the wrath of Cetus, the Sea Monster. The story in Clash of the Titans seems to be borrowed from another story entirely.

Remember Bellerophon? King Iobates of Lycia sent the great hero to kill the Chimaera, a fire-breathing monster that was laying waste to Lycia. The Chimaera was a nasty beast with the head of a lion, the body of a goat, and the tail of a snake. Bellerophon had his work cut out for him.

Luckily, the gods were watching and decided to help. Athena, the goddess of wisdom, gave Bellerophon a golden bridle and directed him to Pegasus, who was peacefully grazing in a field.

Many had tried to tame the wide horse, but it had always flown away. None of the others had Athena’s golden bridle, however. Using it, Bellerophon broke the horse with ease.

Riding Pegasus, Bellerophon rose to meet the evil Chimaera. Again and again, the monster snapped at Bellerophon with its enormous teeth and singed his cloak with its fiery breath, but Pegasus was always able to dart out of the way. Finally, Bellerophon slew the beast with arrows and lance, and Lycia was saved.

Bellerophon became famous from his many subsequent acts of courage. Sadly, the acclaim went to his head. He began to envy the very gods who had helped him in his time of need.

He leaped onto the back of the flying horse with the intention of joining the gods in the sky. Zeus, king of the gods, realized that this could not be. Despite his heroic exploits, Bellerophon was still a mere mortal. Zeus sent a gadfly to sting the horse, and Bellerophon lost control of his flying steed. The hero tumbled to earth, and Pegasus continued its journey.

Zeus loved the horse so much that he chose it to carry his lightening bolts for a while.

Bellerophon did not die. In one version of the story, Athena softened the earth and thus cushioned the hero’s impact with the ground. Instead, he was made lame by the fall and was condemned to wander alone and friendless across the face of the Earth. Few remember his name, and no one marked the place or moment of his death.

Zeus put Pegasus in the sky to honor its memory, and we see the constellation to this very day.

The former hero spent his last days wandering the Earth searching for his beloved horse. How he must have dreamed of his former glory. How he must have remembered flying so close to the heavenly realm on his purest-white, winged steed with the wind whipping though his hair and a world of possibilities ranged below him.

He never found him, of course. Pegasus now soars among the stars. Sadly, all Bellerophon had to do was look up. I wish he had. I hope you will.

Perched off the nose of Pegasus is one of the most beautiful showpieces of the night sky — if you happen to have access to a large amateur telescope. The globular cluster known as M15 looks like a pile of diamond dust in a telescope.

To find it, start with the four stars of the Great Square of Pegasus. Hanging down and to the right of the square is a line of three stars. Take a right from the third star and you’ll come to a bright star named Enif. Keep going about the same distance, and in binoculars or a telescope viewfinder, you’ll find a little fuzz ball. That’s M15. Like most bright globular clusters of its type, M15 is a densely packed ball of stars, extremely rich at the center but relatively sparse toward the edges. What makes M15 visually different is that no matter how big your telescope (and I’ve used some huge ones), it simply cannot resolve the cluster’s center. The stars almost seem to overlap.

It’s one of those mysteries that keeps a stargazer awake nights. Why won’t M15 resolve at its center?

Dozens of globulars like M15 form a halo around the edges of our Milky Way galaxy. The main part of the Milky Way is a discus-shaped collection of stars. Globulars are located above and below the center of the main disk, hovering in the galactic suburbs. M15 is about 33,600 light-years from Earth and contains about 100,000 stars with a total mass of 560,000 stars like our sun. Those 100,000 stars shine with a brightness that is 360,000 times the brightness of the sun. The average star in M15 is thus far more massive and far brighter than our rather pathetic daystar.

The average density of stars in a globular is one star in every cubic light-year. In our section of the Milky Way, you’ll find one star in every seven cubic light-years of space. A light-year is about 6 trillion miles, so even the densely-packed globular stars float in an immense void. Thus, most bright globulars resolve to their cores in telescopes. Because the stars in M15 don’t resolve, they must be incredibly close. Studies of M15 have demonstrated that it is producing copious quantities of X-rays, and astronomers speculate that the intense radiation hints at the existence of a black hole at the cluster’s center. A black hole is a massive accumulation of stellar material clumped so compactly that its gravity prevents even light from escaping. As its heavy gravitational force draws in material, large quantities of space debris swirl inexorably toward the black hole, making it even heavier and richer with gravitational power. As the cosmic debris swirls in, it grinds together and produces the X-rays emanating from M15.

The black hole’s gravitational pull also draws a large number of luminous stars into M15’s central region, a process called core collapse. My telescope cannot resolve the stars in near center because of that stellar traffic jam.

The mystery is solved, but I’m still disappointed. If I just had an even bigger telescope …

Don’t have a huge telescope to observe M15? Consider attending a public program at Perkins Observatory or the John Glenn Astronomy Park. See and <, respectively, for more details.

By Tom Burns


Tom Burns is the former director of the Perkins Observatory in Delaware.

Tom Burns is the former director of the Perkins Observatory in Delaware.