The Stars We
Left Behind

19 February 2020

The constellation Orion in the evening sky.Wikipedia user Nielander
The constellation Orion in the evening sky.

I grew up under dark skies. It was a rare gift for a child. On any clear night I could walk to the middle of the field in front of my parent’s house and behold a night full of stars. I learned to identify constellations at an early age, but the first constellation I learned was Orion.

Orion is an easy constellation to find. Three stars in a line form the belt. Alnitak, Alnilam, and Mintaka. Their names given by early Arabic astronomers. Brilliant blue Rigel marks one leg, while dimmer Saiph marks the other. For the shoulders of Orion there is Bellatrix and the bright red star Betelgeuse.

Betelgeuse is the only star besides the Sun that we can image with detail.ALMA (ESO/NAOJ/NRAO)/E. O’Gorman/P. Kervella
Betelgeuse is the only star besides the Sun that we can image with detail.

Betelgeuse is perhaps the best known star. It is one of the few truly red stars you can see with the naked eye. That’s because Betelgeuse is dying. It is a red giant star. It has been shining for nearly nine billion years, and now its core struggles to fuse elements in its fight against gravitational collapse. As it started to consume heavier elements at a feverish pace, its outer layers expanded and cooled, giving Betelgeuse its red glow. One day Betelgeuse will explode to become a brilliant supernova. It will outshine the full moon before fading to become a nebula. Perhaps it alreay has exploded, and the light is streaming our way as you read this.

Recently Betelgeuse has been dimming by an unusual amount. This has stirred speculation that it will explode soon. Perhaps it will, though it probably won’t. The chance that Betelgeuse will explode in the next century is small.

But Betelgeuse will explode eventually, and that thought fills me with mixed emotions. On the one hand it would be an amazing thing to see a truly bright supernova. The last one occured in 1604. Who wouldn’t want the chance to experience such a rare and wonderous event? On the other hand, if Betelgeuse explodes, the constellation of Orion will be forever changed. The night sky will have changed. A star of my childhood will be gone.

As astronomers we know the sky is not eternal. Stars don’t live forever, and even the constellations change as stars drift through the galaxy. But these changes happen on a cosmic time frame. Within the span of a lifetime they are largely immutable, a childhood companion that will be there for our children and grandchildren. It is a cosmic connection passed from generation to generation throughout human history. It is a connection humanity seems far too eager to break.

Dark skies are becoming increasingly rare. Most children today have never seen the Milky Way. Their night skies are filled with a blue-gray glow of backscattered electric lights and a few of the brightest stars. Most of the stars we see are on a computer screen or a printed page. It is not the same as standing under the stars.

Streaks from Starlink satellites mar the sky.DELVE Survey / CTIO / AURA / NSF
Streaks from Starlink satellites mar the sky.

If you ask someone if they have seen the Milky Way, you get one of two responses. If they haven’t seen it, they’ll casually tell you. But if they have seen the Milky Way, they’ll tell you a story. Of that time they were camping in the mountains and the stars were so bright. Of that time their entire town lost power for a bit, and it looked like there was a glowing cloud over their house. They speak in hushed tones, as if they were standing in a museum or a church. Seeing the Milky Way changes you, even if just a little. In our ferver to undark the night (or fill the sky with thousands of twinkling satellites) we are losing our celestial connection to human history.

When Betelgeuse does finally explode, will it stir us? Will we gather with family and friends in the shadow of Earth to look in wonder at the dying light of an ancient star? Will we feel a connection to those who gazed upon a supernova centuries ago? Or will it merely be the fading glow of the stars we left behind.