Significance behind ‘Keeper of Heaven’ star


March this year came in like a lion and went out like a dead lion. No. Wait. That’s not right. For most people, the real beginning of spring is whenever the weather changes from cold and snow to warmth and rain. Given the strange turbulence of the weather this season, that division was difficult to determine.

For stargazers (this one, at least), spring begins when Arcturus rises again in the east in the early evening. Sadly, poor Arcturus used to be one of the most important stars in the heavens, but now few people except night-sky fanatics can find it.

Let’s rectify that unjust situation.

The easiest way to find Arcturus is to start with the Big Dipper, the brightest stars of Ursa Major, the Great Bear. You’ll find the “Big Dip” high in the northeast around 10 p.m. Follow the handle as it arcs around, and keep going until you come to a bright, yellow-orange star low on the horizon. “Arc to Arcturus,” as the old stargazer’s saying goes.

Because of its closeness to Ursa Major, the Greeks called it the “Guardian of the Bear.” They believed that its power drove the Great Bear across the sky. In fact, Arcturus is the brightest star in the kite-shaped constellation Boötes (boh-OH-teez), the Herdsman. It may seem odd for him and his brightest star to be herding a bear, but there you go.

No. Wait. In fact, Boötes may be a different kind of herdsman than a bear herder. Although the ancient poets never make the connection, an older Greek myth may explain the presence of a constellational herder in the sky that sets it apart from its brightest star.

The myth in question involves the strange case of a baby named Boitos (Boy-EE-tos). The newborn infant was a weakling, so his parents abandoned him to die in an isolated field far from their village. (Poor folks did such things in those days.)

Into the field wandered a herd of cattle, which spied the boy and took pity upon him. They raised him as best they could. Certainly, he was in no want of food. The milk was fresh, and he drank it straight from the spigot, if you know what I mean.

Of the ways of his fellow humans, he knew nothing. When he had finally reached adulthood, he was finally discovered by humans, and what a sight they saw! Boitos walked on all fours, ate grass mostly, and behaved very much like the cows that had raised him.

The humans took him back to civilization and tried to teach him human ways, but he balked at their suggestions. His cow-like behavior ensured that he stood little chance of fitting into human society.

At long last, he withdrew from human company and returned to the herd of cows that had saved his life and provided him with the only real affection he had ever known. He became their cowherd and settled into a long, happy life.

In those days, the gods paid attention to such simple love and devotion and admired it greatly. Thus, when the old cowherd died, they put him up in the sky as the constellation Boötes to remind us that the greatest happiness comes from finding that one true occupation that gives our lives meaning and purpose and simple joy.

Boötes’ brightest star, Arcturus, has special significance in many cultures throughout the world. It is, after all, the fourth brightest star in the sky.

Arcturus is also the nearest bright star to Polaris, the North Star, which does not seem to move from moment to moment or night to night. Arcturus seems to endlessly spin around Polaris and thus hold it in place.

As a result, the ancient Egyptians worshiped it as a god. It was the Arabian “Keeper of Heaven.” To the Chinese, it was the golden “Palace of the Emperor.”

By closely observing its rising and setting, the ancient Greeks used it to set the dates for their annual festival. For most folks in the Northern Hemisphere, it heralded the return of spring, even in places like Egypt, where the winter is not nearly so bad as Ohio’s.

Sailors saw its rising as a harbinger of violent storms at sea, which is not surprising since it rises in the year’s most turbulent month. Around 460 BCE, the Greek physician Hippocrates believed that its position in the sky influences human health. At its rising in the spring, “diseases often prove critical.” One was apt to die at the rising of the star.

Ancient awe eventually turned into scientific fascination. For centuries, Arcturus has been the subject of close scientific scrutiny.

We now know that it is about 37 light-years, or about 220 trillion miles, away from us. At 20 million or more miles in diameter, Arcturus is at least 25 times wider than our sun. Yet, it contains only about the same amount of “star stuff” as our yellow dwarf star. Its stellar material is spread very thinly indeed, with only 1/3,000 the density of the sun.

Our sun has reached the respectable middle age of about 5 billion years old. Arcturus has reached a somewhat premature old age of 7 billion years.

In effect, Arcturus is a harbinger of things to come for our sun. As an “orange-giant” star, it has reached the end of its life. Like Arcturus, the sun will eventually swell to enormous size and engulf its inner planets, perhaps even to the orbit or Earth.

Arcturus will collapse to a white dwarf and die in a few hundred million years, sending its outer shell hurtling outward into space. Our sun will suffer the same fate, but not so soon: in five or six billion years.

Arcturus is a relatively cool star compared to the sun. It is only “orange-hot” at 7,000 degrees Fahrenheit compared to our sun’s “yellow-hot” 10,000 degrees. Such is the fate of old stars. They dim to relative decrepitude before they collapse entirely.

Since Arcturus is relatively close to us as stars go, scientists can actually measure the heat we receive from it. It isn’t much — only about the amount you’d get from a candle five miles away.

For a moment in 1933, Arcturus reached the pinnacle of its fame. At the opening of the “Century of Progress” Exposition in Chicago, the light from the star was focused through telescopes on a photoelectric cell. The energy thus generated was used to flip the switch that turned on a huge bank of floodlights, and the Chicago Exposition was for the first time ablaze with the light, albeit indirectly, of a distant star.

Since then, it’s been all-downhill for Arcturus. Let’s face it. People don’t look at the stars as much as they used to. The very outside lighting used at the Chicago Exposition now illuminates our cities, and the stars have grown dimmer as a result.

Over the long run, the prognosis is bad for Arcturus. It is moving in our general direction at 90 miles per second, and it will reach its closest point to us — at just a few hundredths of a light-year closer — in about 4,000 years. However, its arcing path will eventually cause it to move away. In a few million years, its distance from us will cause it to fade from view, and the “Keeper of Heaven” will desert us for a million centuries.

By Tom Burns


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

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