Leo’s fiercely beating heart


Leo, the regal Lion, creeps higher in the south with each passing day. The Lion is perhaps the most distinctive constellation of spring, and its eventual setting has for a very long time heralded the coming summer.

During the next few weeks just after dark, look for him high in the southeastern sky. You’ll see the distinctive backwards question mark, called the Sickle, which forms Lion’s head and shoulders. To the left, the star ancient Arab astronomers called Denebola represents the Lion’s posterior region.

Regulus, the “Little King,” marks the lion’s front paw or, more traditionally, his beating heart, which is why the ancient Romans called it Cor Leonis, the “Heart of the Lion.”

Regulus is not particularly bright by stargazing standards. Twenty stars in our nighttime sky are brighter. Yet, it shines 288 times more brilliantly than our yellow-dwarf sun and is far younger at only a billion or so years old.

Scientifically speaking, the Little King does not seem at first glance to deserve its royal appellation.

Regulus has at least four dimmer companions in what is referred to as a multiple-star system. They orbit Regulus — or orbit each other orbiting Regulus — in a slow-motion teacups ride in space.

If that seems strange, consider that your own star, the sun, is truly the odd star out. Virtually every star you see in the sky has at least one companion.

Regulus does not appear particularly large. Its mass, the totality of its “star stuff,” is only four times that of our sun. The sum of four suns clumped together isn’t particularly big when one considers that our sun is a dwarf star.

At first glance, its diameter from pole to pole isn’t particularly odd either. At only three times the diameter of our sun, Regulus is dwarfed by practically every star you see at night.

However, the Little King’s equatorial diameter sets it apart. We expect our stars to look like fiery basketballs. At about 4.2 times the sun’s diameter at its equator, Regulus looks more like a football.

Stars are fluid balls of hot gas, and they rotate. The sun rotates about once a month at an equatorial velocity of 4,500 miles an hour. Despite the enormous gravity holding it together as a sphere, you’d expect it to bulge a little at its equator, and it does.

Regulus spins far more rapidly. At an almost unbelievable 700,000 miles per hour, the Little King’s rotation stretches it out almost to the breaking point.

Such rapid rotation has an odd effect on the star’s surface temperature. Its poles are far closer to its center than the more distant equator. Thus, at the equator the force of gravity is lessened somewhat by that greater distance.

Less gravity means a lower temperature. At only 18,000 degrees Fahrenheit, Regulus’s equatorial surface is only a bit less than twice our sun’s temperature.

At the poles, where the force of gravity is greater, Regulus heats up to 27,000 degrees, which approaches three times hotter than our sun. The Lion’s heart beats far faster and burns far hotter than our own.

We have known of Regulus’s strange girth and temperatures only since a 2005 study led by Hal McAlister of Georgia State University.

For most of human history, we saw the star and its parent constellation far differently. Our ancient forebears looked into Leo as if into a mirror that reflected what they cared about most deeply.

The Greco-Roman version of the constellation was somewhat larger than the one we see today. To his right, a beautiful fuzzy patch of unresolved stars called the Praesepe, variously translated as “Beehive” or “Manger,” formed Leo’s whiskers and nose. To the left, a loose cluster of stars in the constellation Coma Berenices represented the tuft of hair at the end of Leo’s tail.

The Chinese saw in the stars of the Sickle their Rain Dragon, to whom they prayed for life-giving rain.

The Taulipang people of Northern Brazil saw Tauna, the god of thunder and lightning. Other Brazilian tribes saw a tasty crayfish.

The ancient Babylonians saw a fierce guard dog, a critical component of commerce. Many such beasts guarded the trade caravans that carried precious cargo from far-away places.

The most recognizable story associated with Leo has to do with the famous hero Hercules. He represents the Nemean Lion, which Hercules killed in the first of his twelve labors.

My favorite story about Leo traces its origin back to the ancient Babylonians. As told much later by the Roman poet Ovid, Leo is the villain in a tale of tragic love and a bloodstained veil fluttering in the breeze.

Pyramus and Thisbe were neighbors separated by a wall and the disapproval of their love by both their sets of parents. Thisbe, the young woman, was forced to talk to her paramour in secret through a crack in the wall.

They agreed to meet one dark night by a spring near the edge of the forest. Thisbe arrived first. Leo arrived soon after. The lion immediately settled down to a meal of the animal he had just killed.

As Thisbe scurried away in terror, she dropped her veil, which the lion picked up in his mouth. In the process, Leo stained the delicate piece of cloth with the blood of his prey. The lion, sated from his repast, then dropped the veil and disappeared into the woods.

The boy Pyramus arrived soon thereafter and picked up Thisbe’s veil. He supposed that Thisbe was dead, and in his anguish used his sword to commit suicide.

When Thisbe returned and saw her dead lover, she plunged his sword into her side. As their blood mingled on the ground, they were united finally in death.

Jupiter, the king of the gods, admired the fervor of young love. He wanted to remind parents that they should be more understanding of their children’s affections. He wanted to impress upon them that unsatisfied youthful passion can lead to tragedy. When we reach adulthood, we must not forget what it was like to be young.

And so it was that he placed the symbol of those dangers in the sky as the constellation Leo. Fluttering behind is Thisbe’s veil, which, in this version of the story, is the beautiful cluster of stars that we have come to call Coma Berenices.

Coincidentally, Jupiter shines brightly in the morning sky right now. At about half a billion miles away, only Jupiter’s immense size and stunning reflectivity can make a planet shine so brightly. It is easy to see why the ancients saw him as a god.

The star Regulus shines more dimly, and there is a lesson in that. I will soon pass my 67th birthday, and on that day, if the clouds cooperate by staying away, I will celebrate by stargazing.

Jupiter is so far away that the light we see took about 50 minutes to get to our eyes. The light from Regulus took 77 years.

If I make it to that advanced age, on my 77th birthday, I will go out and look at the star Regulus. The light that I see at that moment will have erupted from that hydrogen-bomb star on or about the day that I was born and will have been traveling my entire lifetime to get to my eyes and is thus absorbed — erased — never to be seen again.

As I look upward at the Little King, I will contemplate the brevity of human life, the long-lost passion of my youth, my love and forbearance for my own children, and the immensity and beauty of the cosmos, which we all are privileged — in our small way and for our brief time — to be a part of.


By Tom Burns


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

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