A dot in the sky
During our public programs at Perkins, the educational process often takes interesting turns. One cold, clear night a while back, I listened in on a father and son who had stepped away from the rest of the group to check out a few constellations.
The son was astronomically savvy. His father was, well, not. The boy pointed out the V-shaped collection of stars that form the head of the constellation Taurus, the Bull. His small finger pushed up at the sky as he taught his father to find the sideways V’s bottom left star, the brightest star in the constellation, called Aldebaran. “You mean the orange dot?” the father asked.
I suppose that from our limited human perspective, which is so far from the tumultuous action of the stars, those heaving hydrogen bombs are indeed tiny dots.
However, appearances can be deceiving. At 60 light years distant, it is 3.5 million times farther than our own star, the sun. Having fused its hydrogen fuel into helium for billions of years, it has reached the end of its life. During its halcyon days, its total amount of material was probably less than three times that of the sun, putting it in the sun’s stellar ballpark. If we want to know what the sun will look like in 5 billion years, we should look in Aldebaran’s direction.
Aldebaran’s mass may be similar to the sun’s, but it is currently 40 times wider at perhaps 40 million miles in diameter. If we removed the sun from its place in our solar system and replaced it with Aldebaran, that behemoth would extend nearly to the orbit of Mercury.
In effect, it has become a ghost of its formerly sun-like self. More than 100 million years ago, Aldebaran swelled from a sun-sized star to a much larger size, a change that took only a few million years. Since it didn’t gain any material when it swelled, its gases became exceedingly thin and spread out — a red-hot vacuum that is barely there at all. The star still produced about the same amount of energy, but that output was spread out over a much larger surface area.
Deep in its center, its rate of hydrogen burning increased significantly, causing it to swell even further over the next 100 million years. Although its energy output increased, its larger size caused its surface temperature to decrease even more. As a result, its temperature decreased from a yellow-hot, 10,000-degree fury to a relatively sedate 6,000 degrees.
Over the next 100 million years, Aldebaran will shrink and expand several times until the fuel at its core is exhausted. It will then collapse to a tiny white dwarf, an extremely dense ball of dead star no wider than our puny planet Earth.
I can imagine the father saying,“ So what?” So this. The history of Aldebaran is the history of our sun. As we look at this little dot, we are looking at the future of our own speck-like Earth in the far distant future as it orbits the dot-like star we call the sun.
The point is that every star has its story. Like individual humans, that story is small compared to the overall history of the universe. Like specks of dust floating in a cold, winter breeze, they drift all-too briefly into the light before they are lost again in darkness. For that ephemeral moment, they shine with indescribable glory.
And as I stood in darkness apart in from that father and son during that tiny fragment of time, I felt the sad, beautiful panorama of that history. As they stood silhouetted against the stars, I felt like that speck of dust floating on a winter’s wind. The words were in my throat, but I never would presume to disturb their precious moment under the stars. So here they are: “If a Aldebaran is just a dot, then what in heaven’s name are we?”
Tom Burns is director of Ohio Wesleyan University¹s Perkins Observatory in Delaware. He can be reached at tlburns@owu.edu
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