Betelgeuse Dimming but Not Ready to Blow

Betelgeuse was dimming over the holidays, leading stargazers to speculate about a supernova. Find out why none of us will live to see it.

Growing up in Canada, one of the first constellations I learned to spot was Orion. I started out learning about the two dippers and how to locate the North Star.

Everyone wants you to know that in case you get lost. After that, because the winter sun sets so early in Canada, Orion is impossible to miss in the night sky at that time of year.

It’s a sort of a stick figure man if you use its stars to connect the dots. Up in the top left corner of the figure’s outline, there is a red star.


It’s officially the eleventh brightest star in the sky, even though it’s over 600 light-years away. This red star is bright but nearby Rigel and Sirius are even brighter. All these brilliant stars in one place are what make the constellation of Orion so unmistakable.

The star’s name is Betelgeuse. We’re not talking about the alien character in the movie from the 80s. Sometimes it’s brightening and at other times, like now, Betelgeuse is dimming.

I’ve been told that Betelguese means “armpit of the hairy one.” Its scientific name is Alpha Orionis

SCIENTIFIC NAme is alpha orionis

Betelgeuse is located just about where the stick figure’s armpit, or maybe his shoulder, should be. It’s always been an interesting star.

The red supergiant is a comparatively young star at less than 10 million years old. Yet, in human terms, because it’s so hard to miss, it’s been talked about for a very long time, in fact as far back as anyone can remember. The Inuit called it Ulluriajjuaq, which means “large star”.

The ancient Chinese discussed it, saying that it was a shade of yellow. If that’s true, it might mean that Betelgeuse used to be a yellow supergiant 2,000 years ago.


Ptolemy mentioned it, including how “ruddy” or reddish it was. That’s more in line with our modern idea that it’s a red supergiant star.

To get an idea of how big a supergiant is, its helpful to imagine Betelgeuse as our sun. If we placed it in the centre of our solar system, Betelgeuse would reach out past the asteroid belt, maybe even as far as Jupiter. It’s roughly 20 times larger than the sun.

In Victorian times, John Herschel was the first astronomer to discover that Betelgeuse was a variable star. He found that in October 1837 and November 1839, Betelgeuse was even brighter than Rigel and that at other times, Betelgeuse was dimming.


This brightness rivalry between the two is probably why Johann Bayer decided to call it Alpha Orionis in 1603. Today, we would give that designation to Rigel.

Apart from the sun, Betelgeuse represented the first time scientists were able to measure a star’s surface area.

Betelgeuse has been big news in the last few weeks. Researchers led by Edward Guinan at Villanova University released a note on Betelgeuse showing that the bright red star had dimmed from being the 10th brightest to the 23rd brightest star in the night sky. They published their note in The Astronomer’s Telegram.

That made it fainter than the neighbouring star Aldebaran, which is odd. This is the faintest that Betelgeuse has been in more than a century.


Stars like Betelgeuse eventually end in a supernova or massive explosion. Scientists forecast that this will happen to Belegeuse within the next 100,000 years. Martin Mobberley explains this process in his book Supernovae: and How to Observe Them (Astronomers’ Observing Guides).

This peculiar dimming has led to speculation that Betelgeuse will explode shortly. If that were to happen, Betelgeuse would give off a spectacular burst of light, making it brighter than the full moon.

It would then start to fade. After about three years, it would be back to the brightness we see today, and within six years we would no longer see it with the unaided eye.


This raised quite a sensation on social media over the holidays. Unfortunately for stargazers looking for something fun to watch over the next half-dozen years, it’s not going to happen that way.

As we mentioned above, Betelgeuse is a variable star. The changes that Herschel noticed in the 19th century are no different from the dimming we see today.

As Professor Larry Monlinar of Calvin University put it, “If we look at the past brightness of Betelgeuse, it has gone up and down. It could still be a million years before it explodes.”


Professor J. Craig Wheeler of the University of Texas in Austin concurs. “My money all along has been that Betelgeuse is going through a somewhat extreme, but otherwise normal quasi-periodic change in brightness.”

Alexei Filippenko, an astronomer at the University of California, Berkeley was even more blunt, telling us not to hold our breath, “unless you’re good at holding your breath for 100,000 years.”

The problem is that scientists still lack a good handle on how stars behave at the end of their lives. Supernovas don’t happen very often, and the ones we’ve had lately have been in distant galaxies where we don’t know much about the star involved.


There are several theories about why Betelgeuse is dimming. Whatever ends up happening, the current focus on the red supergiant will teach us more about the final stages of a star’s life.

We always have more to learn if we dare to know.

Learn more:

New York Times
The Fainting of the Nearby Red Supergiant Betelgeuse
Supernovae: and How to Observe Them (Astronomers’ Observing Guides)
Newborn Stars Bringing Forth Solar Systems
The Many Ways the Constellations Reveal Themselves
Exoplanet Giant Orbiting Tiny White Dwarf

Cosmic Collision Makes Gravitation Waves


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