Stars that help form Orion’s Belt


By Tom Burns - Stargazing



This week’s column is difficult to write. I want to tell you about the belt stars of the constellation Orion, but I’m puzzled about how to phrase their geometric relationship with each other.

The issue has to do with a peculiar difference in how we refer to queuing in America. Say you’re waiting with several people to check out of your local grocery.

The group of people you are waiting with is commonly called a “line,” even in these pandemic days when the line often isn’t linear. I might call the queuing situation standing “in line,” but I frequently hear it called standing “on line.”

The latter description makes absolutely no sense to me. It assumes a line on the ground and people standing on it.

I have looked on several occasions, and the line in question appears to be entirely imaginary. In fact, the humans standing there actually constitute the line. Therefore, they are in it and not on it.

If all this sounds silly (and it is, of course), consider the way NASA refers to satellites they have launched into orbit around Earth. Their spokespeople always say that the satellite is “on orbit,” as if there is some tangible line the object is traveling on. However, the satellite forms the orbit as it goes. Thus, it is in orbit, thank you very much.

Those folks reading this piece online (ha!) should feel free to comment on this issue.

In the meantime, allow me to say that it’s hard to miss the three belt stars of Orion. They are of about equal apparent brightness in an almost equally spaced line.

But that description doesn’t do them justice. Alfred Lord Tennyson, a 19th-century British poet, does a better job:

“Those three stars of the airy Giant’s zone

That glitter burnished by the frosty dark.”

Look for them — and the rest of Orion — about halfway to zenith (the top of the sky) around 8:30 p.m. right now. The Hunter’s belt tilts slightly to the left, but it is still more horizontal than vertical.

The three belt stars are among the most famous in the nighttime sky. Many cultures throughout history and around the globe have their own unique names for what we call Orion’s belt.

Roman writers referred to them variously as Zona (Girdle), Balteus (Belt), Jugula (Neck), and Scabbard, i.e., the sheath of Orion’s sword.

The Masai people of Africa combined the belt stars with Orion’s sword, which hangs from his belt. According to constellation scholar William Olcott, they called the group “three old widows following three old men. Also, Olcott writes that the Basuto people of Africa called the belt stars the “Three Pigs.”

The indigenous people of Australia referred to it as three dancing Young Men.

Throughout western history, some religious scholars have identified the three stars staff of Saint Peter or the prophet Jacob.

One of the most notable biblical references appears in the Book of Job.

Job is upset with God because he has tried mightily to follow God’s law, but pain and poverty are all he’s received in return. There seems to be no justice in the world. In response, God asks Job, “Canst thou bind the chains of the Pleiades, Or loose the bands of Orion?” (Job 38:31)

Of course, Job can’t, but that doesn’t mean that the “bands” aren’t coming loose already, as we shall see.

Occasionally, even the names of such star groupings become embroiled in politics. In 1807, the University of Leipsic (modern Leipzig) attempted to rename the belt stars after Napoleon Bonaparte, who had ostentatiously crowned himself Emperor of Europe in 1804.

The university granted the name in academic retaliation for Napoleon’s devastating defeat at the hands of Admiral Alfred Lord Nelson at the Battle of Trafalgar in 1805.

It was a rather silly thing to do, of course. For obvious reasons, the name did not stick.

Early Arabs referred to the three stars as three vertebrae in a person’s back, three golden grains or nuts, or simply Al Nasak, the Line.

Eventually, medieval Arab astronomers settled on three names for the stars — Mintaka, Alnilam and Alnitak — that we still use today. Oddly, each of the stars’ specific designations refers to the group of three stars collectively.

The right-most star of the belt is called Mintaka, an Arabic word that means “Belt.” It is the closest of the three stars at 1,200 light-years away. At six trillion miles per light-year, that’s pretty distant as far as bright, naked-eye stars go.

Mintaka is a multiple-star system of at least five stars gravitationally bound together. The star we see is the system’s primary star.

Its brightness in the sky results from its phenomenal energy output. Mintaka is a hot, young, blue star producing 190,000 times more energy than our daystar, the sun.

But Mintaka is a piker compared to the middle star of the belt, a ferocious energy-producer called Alnilam, the “String of Pearls.” As a blue-supergiant star, Alnilam emits an estimated 537,000 times more energy than the sun and is extremely hot by our terrestrial standards at about 50,000 degrees Fahrenheit on its surface. (Compare that to the sun’s rather chilly 10,000 degrees.) It is also the belt’s farthest star at about 2,000 light-years away.

The belt’s left-most star is named Alnitak, “The Girdle.” Like Mintaka, Alnitak is a multiple-star system, but its system contains only three stars.

At a mere 35,000 suns, Alnitak’s energy production is relatively low compared to the other two belt stars. It’s a bit farther from us than Alnilam at 1,260 light-years.

In fact, the belt stars are not in a line at all — or on one either. The three stars look bound together like the holes in a belt.

However, that appearance is an illusion based on our Earthly point of view, which is no more important than the point of view from any place in our Milky Way galaxy of 300 billion stars.

Note the distances to the stars from Earth given above. The two stars closest to each other, Alnilam and Alnitak, are at least 60 light-years away from each other. Compare that with the distance of our sun with Proxima Centauri, the closest star to it. Proxima is a scant 4.2 light-years away from the sun, and the two stars can hardly be called “bound,” gravitationally or otherwise.

Thus, Orion’s girdle is composed of stars located at incredible distances from each other. If you stood on any planet orbiting any other star, the illusion of the line would disappear.

And the stars are “unbinding” even further. As you read these words, they are moving away from each other at ungodly velocities. If humans survive to look at the heavens in the far distant future, Orion’s belt will have disappeared. Its stars will scatter to the far ends of the great deep.

As for the “on” and “in” thing, it turns out to be a function of regional dialects. New Yorkers and NASA spokespeople use “on” instead of the more logical “in.” But nobody ever claimed that language was logical in the first place. If you don’t believe me, check it out in-, er, online.

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By Tom Burns

Stargazing

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

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