Betelgeuse, Betelgeuse, Betelgeuse--Open Science Thread

A fairly nearby star is starting to act in weird ways . . .

If you have ever gazed towards the night sky in the winter, you may be familiar with the constellation Orion, the ancient Greek hunter, and the very bright red star in the upper left arm of Orion, called Betelgeuse:

(Source: Orion_constellation_map.png: Torsten Bronger derivative work: Kxx (talk) - Orion_constellation_map.png)

Betelgeuse, a red super-giant star, is highly unusual. The late, great Jack Horkheimer (aka, The Star Hustler), probably had the best description of Betelgeuse:

If you go out February 14th, Valentine's Day night between the hours of 8 and 9 p.m and look due south you'll see what I like to call the Valentine's Day star because every Valentine's Day night between 8 and 9 p.m. you'll see a very bright red star shining at its highest above the horizon. In fact it is the brightest red star we can see with the naked eye . . . It marks the shoulder star of the great sky giant Orion the Hunter and its name is Betelgeuse which in arabic means 'the armpit', which isn't very romantic for Valentines Day. But if you want to give your beloved a really big Valentine, well this is about as big a one as you'll ever find.

You see, if we compare Betelgeuse, our Valentine star with our own star, the sun, and our own planet earth, you will understand just how big. Now we all know that our 8,000 mile wide earth is pretty dinky compared to our 865 thousand mile wide sun. In fact we could fit over 1 million earths inside our sun. Betelgeuse, however, is so humongous we could fit over 160 million of our suns in side it! And that's when it's at its smallest size. You see, Betelgeuse is one of those stars which changes its size regularly like a slowly beating heart. It beats about once every 6 years and when it is fully contracted and at its minimum size it is about 500 times the diameter of our sun but when it expands to its maximum size it is almost 900 times as wide. Or if you care to think of it this way, if we could place Betelgeuse where our sun is, even when it is at its minimum size, it would stretch out past the orbits of Mercury, Venus, Earth, all the way to Mars. But when it's at its maximum it would reach all the way to Jupiter. Wow!

So there you have it, a humongous cosmic Valentine. A giant red star slowly beating like a heavenly heart for your sweetheart, courtesy of our local galaxy, and you can see it any and every clear Valentine's night, between 8 and 9 p.m., at its highest above the horizon, just look due south.

(Source: )

You see, Betelgeuse is a very unstable star--it has already fused all of its Hydrogen and is now fusing its internal Helium, which indicates it is not far from the end of its life (in relative, stellar terms of time). In fact, a couple decades ago, scientists thought it would end its life in a supernova explosion at some point in the next 1 million years--but more recent estimates with better equipment indicate it will go supernova at some point in the next 100,000 years!

But . . .

Since this past September (2019), Betelgeuse has been dimming to an unprecedented extent, never before observed in 100 years of observation. In the last week, its dimming has slowed (although not stopped), so it may end up being nothing, but it is no longer the brightest star in Orion for the first time in 180 years of scientific observation, and its brightness has decreased by an amazing 25%.

The Continued Unprecedented Fading of Betelgeuse

What is happening? From the above:

However, as pointed out by others, the current fainting episode could also arise from expelled, cooling gas/dust partially obscuring the star. The recent changes defined by our V-band/Wing photometry seem best explained from changes in the envelop-outer convection atmosphere of this pulsating, unstable supergiant. If these recent light changes are due to an extra-large amplitude light pulse on the ~420-day period, then the next mid-light minimum is expected during late January/early February, 2020. If Betelgeuse continues to dim after that time then other possibilities will have to be considered. The unusual behavior of Betelgeuse should be closely watched.

Perhaps the star just expelled some gas or dust, obscuring itself to an unprecedented extent. Or, if the dimming continues past early February, perhaps this could be the end of it?

On the off chance that Betelgeuse goes supernova, what would happen?

The star would suddenly turn into a Type II supernova. These have a number of different visual results, but here is one recent example from another galaxy:

(Courtesy: NASA)

The supernova explosion would have half the brightness of the full moon for a couple of weeks. It would slowly fade to the brightness of the planet Venus over a couple of years, and then as the years went on, it would fade and disappear entirely. Orion would lose its left armpit--its club-carrying arm that was battling the constellation Taurus the Bull, which is next to it. It would be quite the thing to observe, and change our sky forever!

Since Betelgeuse is relatively near, would the Earth be in danger?

Thankfully, the answer is "No". We're not exactly sure how far away the star is--somewhere between 520 and 700 light years (considering our Milky Way galaxy is 150,000 light years wide, that's pretty darn close!). But, at that distance, the remnants of the supernova would slow and disperse into dust and the interstellar medium long before they ever reached the Earth or our solar system. There might be electromagnetic interference for a period of years, but that's the likely extent of damage. If the star was 150 light years away or closer, the story would be very much different!

Perhaps if you are so inclined, and have a camera or mobile phone with a tripod, maybe get a long-exposure photograph of Orion in the upcoming week. There is an off chance that you might just end up with one of the final photographs of the full constellation Orion!

Open thread for science and the like!

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edg's picture

I could swear I once saw a documentary where the spelling was Beetlejuice. I recall Michael Keaton as the narrator.

All kidding aside, thanks for writing this essay. Here's a photo of Betelguese from Mother Nature Network:

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Lookout's picture

Red Giants

After burning for billions of years, a main sequence star will eventually exhaust its fuel supply as the majority of its hydrogen is converted into helium through nuclear fusion. At this point in the life cycle of a star, the excess helium causes the star’s temperature to increase. When this occurs, the star will expand to become a red giant.

Red giants are bright red in color. They are also larger and much more luminous than main sequence stars. As the red giant’s core continues to collapse under the force of gravity, it will become dense enough to convert its remaining supply of helium into carbon. This occurs over an approximately 100 million year period, until it is time for the star to die. Just as mass will dictate the luminosity of a star, it also will determine the manner of a star’s death.
White Dwarfs

Main sequence stars that have lower masses ultimately become white dwarfs. Once a red giant has burned through its helium supply, the star will lose mass. Its remaining core of carbon will continue to cool and decrease in luminosity over billions of years until it becomes a white dwarf.

Eventually, the white dwarf star will cease to produce energy altogether and darken to become a black dwarf. White dwarf stars are smaller, denser and less luminous than red giant stars. The density of white dwarf stars is so great that a mere spoon of white dwarf material would weigh several tons.

I'm no astrophysicist but it depends on the mass of the star to my understanding...

Once stars that are 5 times or more massive than our Sun reach the red giant phase, their core temperature increases as carbon atoms are formed from the fusion of helium atoms. Gravity continues to pull carbon atoms together as the temperature increases and additional fusion processes proceed, forming oxygen, nitrogen, and eventually iron.

When the core contains essentially just iron, fusion in the core ceases. This is because iron is the most compact and stable of all the elements. It takes more energy to break up the iron nucleus than that of any other element. Creating heavier elements through fusing of iron thus requires an input of energy rather than the release of energy. Since energy is no longer being radiated from the core, in less than a second, the star begins the final phase of gravitational collapse. The core temperature rises to over 100 billion degrees as the iron atoms are crushed together. The repulsive force between the nuclei overcomes the force of gravity, and the core recoils out from the heart of the star in a shock wave, which we see as a supernova explosion.

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“Until justice rolls down like water and righteousness like a mighty stream.”

@Lookout @Lookout

and definitely has the mass to go supernova. There's pretty much no doubt that is how it will eventually (within the next 100,000 years) end its life.

It is actually one of the largest stars known. If you look at the chart below, which shows six panes of increasingly sized planet and stellar objects, Betelgeuse is the first one on the last pane (6), compared to the largest star (VY Canis Majoris) that we know of, which is the last one in the last pane:

(Source: Image By Dave Jarvis ( - Own work, CC BY-SA 3.0,

It is not a main sequence star. In fact, whereas our Sun (very much a main sequence star) has been around for 4.5 billion years or so, Betelgeuse has only existed for 8 or 9 million years. Even when our Sun exhausts all its hydrogen--5.4 billion years from now--and reaches its red giant stage, it won't compare with Betelgeuse, whose size varies between the orbits of Mars and Jupiter. The Sun may or may not reach the orbit of the Earth (it's a matter of debate), and it is much less massive than Betelgeuse. The Sun will, indeed, not explode, but last for 120 million years as a red giant, and then shrink into a white dwarf star, where it will remain for trillions of years.

That's a very nice explanation of a supernova that you provide! Thanks for sharing that!

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Cassiodorus's picture

@Lookout iron contains the least massive protons and neutrons of any of the atoms, so to convert an iron atom into any other atom forces the reverse process, of energy back into matter.

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"The only possible good outcome for most Americans is a Sanders win. No other path leads anywhere decent." -- Ian Welsh

Iron is at the lowest point of the curve. To transmute to another element requires energy input. Heavier elements, like Uranium, can break apart (fission) releasing energy. Lighter elements like Hydrogen can stick together releasing energy (fusion) bit iron is at the bottom of the valley with nowhere to go. Hydrogen is at the farthest extreme of fusion energy, and plutonium is at the farthest extreme of of fission energy.

Betelgeuse is burning helium. Two heliums would combine to make berylium-8 but be-8 is extremely unstable and won't stay stable. IIRC a nanosecond would be eternity for a Be-8 nucleus. More like femtoseconds. So, to burn Helium, three alpha particles have to simultaneously collide and stick forming Carbon-12. Then carbon-12 can capture a Helium nucleus forming oxygen-16 ... You see where the common elements come from?
Each burning is further down the curve of binding energy so it releases less and less energy. The dying star goes through them very quickly. Elements heavier than iron absorb energy so they are not formed by fusion except in the supernova where they do not contribute to the explosion but absorb energy from the explosion. So they are rare, like gold and uranium.

At least that was the picture when I went to grad school in the '70s.

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Tulsi Gabbard 2020 !

Lookout's picture

@The Voice In the Wilderness

Stars are element generators.

We are stardust
billion year old carbon
We are golden
stuck in a devils bargain
and we've got to get ourselves back to the garden

8 users have voted.

“Until justice rolls down like water and righteousness like a mighty stream.”

Cassiodorus's picture

@The Voice In the Wilderness except for a smaller audience.

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"The only possible good outcome for most Americans is a Sanders win. No other path leads anywhere decent." -- Ian Welsh

that's all.

1 user has voted.

Tulsi Gabbard 2020 !

Raggedy Ann's picture

I found it interesting and informative. Living in the country with little light pollution, I can see the stars very clearly. I'll go find Betelgeuse tonight and try and keep track of it - especially 2/14! We're expecting storms, so I'm hoping for a few clear nights between now and then.

Cheers! Drinks

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“The trouble [with injustice] is that once you see it, you can’t unsee it. And once you’ve seen it, keeping quiet, saying nothing, becomes as political an act as speaking out. There is no innocence. Either way, you’re accountable.”
-- Arundhati Roy

mhagle's picture

Against the southern horizon around 8 or 9? Cool. Thanks!

Nice break from politics!

6 users have voted.


"Make dirt, not war." eyo

@mhagle @mhagle @mhagle

If you are familiar with it, just look for Orion. The 3 star belt is the obvious thing in the sky, with two bright stars above the belt for each arm, and two below it for each leg. Betelgeuse is to the upper left, as shown in the star diagram in the original post. It is a very red star, but is right now much dimmer than it usually is.

Just underneath the belt is a slightly blurry patch (M43/M42 on the start chart mentioned) that is visible to the naked eye, but difficult to make out exactly what it is. This is actually the Orion Nebula--about 1,344 light years away (2-3 times more distant than Betelgeuse)--and is the closest place to Earth that stars are actually be formed and 'born'. It looks like this in a powerful telescope:

(Public domain image.)

If you follow Orion's right arm above his belt (the non-Betelgeuse arm), and continue to follow that upwards and at an angle, you will find not far away the bright red star Aldebaran, which is the eye of the bull Taurus, which Orion is ready to smash with the club held in his left hand.

If Betelgeuse (the red star in the image below) goes supernova, in a decade or so, Orion's left arm, which holds his club, will disappear, putting him at a distinct disadvantage in his eternal fight with the mythical bull!

(Source: Sanu N [CC BY-SA (])

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@apenultimate drawing of the hunter figure, it is interesting that the huge star nursery, where stars are born, turns out to be located, appropriately, just beneath the belt stars.

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@apenultimate Was on a night drive in South Luangwa National Park and things were relatively quiet. What that means in game drives is there were no "things with teeth out hunting. We were enjoying the other sights and sounds and magnificent stars above when two people in front of us started talking about the stars. One of them was Muslim and he said, he could always know which way to find Mecca by finding the stars in Orions belt. Not real sure about geography and if this is correct but our drive and guide stopped the vehicle and asked if we would like an astronomy lesson since we had no light pollution. He then proceeded to show us all of the constellations visible to us and then we continued on our journey. Cannot remember all of the constellations but was so amazed our driver/guide knew so much about the stars. Night to remember.

6 users have voted.

Life is what you make it, so make it something worthwhile.

This ain't no dress rehearsal!

So there has to be more than that to it. I knew this as a boy but I've forgotten. Perhaps the belt points the way to Polaris which tells you where North is and then something else.

Who's up on Celestial Navigation.

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Tulsi Gabbard 2020 !

@The Voice In the Wilderness @The Voice In the Wilderness
The constellation Orion begins to rise in the night skies come fall.
It is one of the indicators of the coming winter. It rises later each day
until spring envelopes it in daylight.

The pole pointers you mentioned are located in the Big dipper.
The two almost vertical stars in the scoop point to Polaris (north star)
which is the end of the handle of the little dipper (Ursa Minor).

Some useful memory cues to locate navigation stars--

The three stars in the spring triangle asterism ~
Following the handle of the big dipper:
Arc to Arcturus (in Bootes)
Spike to Spica (in Virgo)
then look east to locate the apex ...
Regulus (in Leo) -- or Denebola in Leo's tail


Cassiopeia can be found in what appears to be a 'W'a bit
to the east of Polaris

“He pointed out to him the bearings of the coast, explained to him the variations of the compass, and taught him to read in that vast book opened over our heads which they call heaven, and where God writes in azure with letters of diamonds.”

― Alexandre Dumas, The Count of Monte Cristo

Fun stuff!

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May we be united and strong -- laurel

unless you already know the direction of the rising Orion and know where you are.

2 users have voted.

Tulsi Gabbard 2020 !

@The Voice In the Wilderness @The Voice In the Wilderness
local legend I assume.
One trick is to find Polaris first in the northern hemisphere.
First you find the big dipper.
Follow the two vertical stars at the end of the scoop up.
They point to the end of the handle of the little dipper.
It is sort of an upside down shape of the big dipper
only smaller, towards the west.
The last star in the handle of little dipper
is the north star which aims
toward true north - the north axis of earth's spin.

Once you find north, all the other directions are laid out.
Face north, your right hand points east
where the sun comes up
Left hand points west toward sunset.
Your back is facing south, the plane of solar gain.
Again, facing north look up and notice the stars / sun
appear to be moving right to left.
They are not moving.
We are spinning clockwise, if observed overhead.
The sun, moon and stars appear to be going
anti-clockwise thru the dome.

Hope this helps!
Looking up,

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May we be united and strong -- laurel

2 users have voted.

Best teacher I ever lucked into having gave us astronomy units (among other subjects not traditionally taught to small children) when we were just 7 and 8. She taught us some of the science and some of the mythology, then took us all on a weekend camping trip in Everglades National Park with the star maps we'd drawn in class so we could find all those constellations in the sky. Orion the Hunter is among the easiest ones to find so many of us were able to tag that one first. We were all so excited to stay up late around the campfire together stargazing and our teacher and the park rangers told us stories well into the night. Still remember the childhood awe of that, and still look for Orion every time I'm out under the night sky.

Thanks for the heads up and the Horkheimer down memory lane, will keep watching the sky!

5 users have voted.
Daenerys's picture

Here is a photo of Orion I took last year:

I used the moon setting on my camera (Nikon Coolpix P900), then once uploaded I cranked brightness and contrast all the way up to bring out more stars. You don't get the red color of Betelgeuse, but I like how it turned out. Astrophotography is tricky; on my camera I couldn't make out any stars through the viewfinder on night settings, so I just had to point and hope I got what I was looking at when I pressed the shutter. Maybe it shows up better on the screen, IDK. I have yet to see the northern lights since moving back to MN too; that's something I really want to photograph with it.

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This shit is bananas.