Betelgeuse is a red supergiant star located 640.5 light years from Earth, in the constellation Orion. The star is located in the upper-left corner of Orion the Hunter, forming his shoulder. It is one of the largest stars visible to the naked eye. Ancient people took note of the spectacular star, and astronomers today continue to study its mystifying nature. Read on to explore these and other interesting star facts about Betelgeuse.
| Betelgeuse Star Profile | Figures |
| Age | 10 – 12 million years old |
| Distance from Earth | 640.5 light years |
| Location | The constellation Orion |
| Magnitude Ranking | 0.42 apparent magnitude/9th brightest overall star (on average) |
| Mass | 9.5 – 21 solar masses |
| Star Type | Red Supergiant/ Semi irregular variable star |
| Temperature | 3590 °K |
Ancient Star
With its distinct color and obvious brightness, Betelgeuse has always stood out in the sky. Ptolemy made note of the star, describing its ruddy color. The Italian astronomer Angelo Secchi included Betelgeuse in a class of stars he designated Class III stars, which were orange to red stars. He did so in the nineteenth century before the use of any modern systems for classifying stars became commonplace. It is interesting to note that though Betelgeuse has been recognized since antiquity, it has not always been associated with the distinct red color we are familiar with today.
Centuries prior to Ptolemy’s observations, Chinese astronomers observed that Betelgeuse had a yellow color. Their descriptions reveal that Betelgeuse was possibly seen during a yellow supergiant phase three centuries ago.
Sir John Herschel also paid special attention to Betelgeuse, which is an irregular variable star. He noted that the supergiant varied in brightness in 1836, and continued to examine Betelgeuse’s changing magnitude for years to follow. He documented the significant changes in brightness from 1836 to 1840, including Betelgeuse outshining Rigel (the brightest star in the constellation Orion) in October 1837.
The dramatic and sometimes seemingly sporadic changes in Betelgeuse’s magnitude make an excellent explanation for why Johann Bayer incorrectly designated Betelgeuse as α Orionis. Bayer had a system of classifying stars in a constellation by their magnitude, meaning that the star designated as alpha was the brightest in the constellation. Despite its brilliance, Betelgeuse is the second brightest star in Orion after Rigel. This means that Johann Bayer must have observed Betelgeuse close to its maximum magnitude.
The Inuit people also ranked Betelgeuse as being brighter than Rigel. Betelgeuse is higher in the sky than Rigel when seen from Arctic latitudes, and along with its obvious red color, the Inuit took it as being the brighter of the pair.
Betelgeuse Mythology
Betelgeuse has a rich mythology to add to its long history in human culture. The star is mentioned in a medieval Japanese epic of two clans engaged a war for control over the nation. The Taira or Heike tribe of Japan took Betelgeuse and its red color as their symbol. The opposing clan, the Minamoto or Genji Clan took Rigel and its white color as their symbol. The stars represented the clans facing off, symbolic of the legendary war.
In Tahiti, Betelgeuse is regarded as one of the pillars holding up the sky.
In some South-American cultures, Betelgeuse represents the severed limb of a man (Orion) whose wife cut off his leg. The Lakota people of North America also see a man whose arm has been cut off. Native peoples of Australia noted the giant star’s varying brightness, calling the star “Owl Eyes Flickering”. In traditional South African cultures, Betelgeuse represents a lion while the three stars of Orion’s belt represent three zebra.
What Does Betelgeuse Mean?
Betelgeuse gets its offbeat name from a mistranslation from the Arabic Yad al-Jauzā’ meaning “the Hand of al-Jauzā” or “hand of the central one”. It is likely the “y” was poorly or accidentally translated into a “b”. The star’s name is most often pronounced BET-əl-jooz, BEET-təl-jooz, and BEET-əl-joos depending on dialect, and has also been pronounced bet-əl-GURZ, though far less commonly.
Betelgeuse Location
Betelgeuse is a beautiful and easily recognizable star thanks to its bright red appearance and location in the well-known constellation Orion the Hunter. Betelgeuse is widely visible across all inhabited regions of Earth for several months throughout the year. At these times, only inhabitants in Antarctica would not be able to see the giant star.
Betelgeuse typically makes an early New Year appearance for observers in mid-northern latitudes, where the star can be seen above the horizon around sunset. January and February evenings are some of the best times of year for northern observers to view Betelgeuse. You can spot Betelgeuse as the bright red star in the upper left corner of the rectangle that outlines Orion.
Betelgeuse also forms part of the Winter Triangle Asterism along with two other stars and is the center of the Winter Hexagon.
The star lies 640.5 light years from Earth. Astronomers believe that Betelgeuse formed around 10 – 12 million years ago as part of the Orion OB1 Association; a high mass cluster of hot and giant stars. The stars that form Orion’s famous belt likely come from the same association of stars.
The Milky Way is surprisingly ordered. All bodies in the galaxy orbit around a common central mass, most in the same direction and with similar speeds. Runaway stars are stars that appear to be moving faster across space or in a different direction from the norm.
Betelgeuse is one such runaway star that was ejected from its birthplace is the Orion OB1 Association; flung into space millions of years ago. Scientists have witnessed Betelgeuse speeding through the interstellar medium at 30km/s. Such a massive star racing along at these supersonic speeds creates a bow shock that extends for four light years.
For everything that is so excessive in Betelgeuse’s nature, the star is a slow rotator. It spins around with a velocity of 5km/s according to most recent recordings. This is much slower than Antares – another red supergiant – which has a rotational velocity of 20km/. Astronomers calculate that it takes the giant star 8.4 years to complete one rotation on its axis.
Betelgeuse Mass
Betelgeuse is a massive star that evolves rapidly and has quite a few peculiarities. Determining Betelgeuse’s mass has been no easy feat, and even today scientists continue to find better methods at calculating the red supergiant’s mass more precisely. Betelgeuse has no orbital companions that we know of, which eliminates an effective method of directly calculating a star’s mass by analyzing its orbital companions.
Modern efforts to determining Betelgeuse’s mass produce varying values. On the low end of the scale Betelgeuse may be over 7 solar masses, and on the far end of the scale, Betelgeuse may be 21 times more massive than the Sun.
Scientists calculate that the supergiant possibly began its life as a star 15 to 20 times as massive as the Sun. Astronomers analyze the star’s luminosity to help determine this value. Betelgeuse is not only more massive than the Sun, but also approximately 600 times wider than our home star, and with a volume 200 million times greater than the Sun. The stars incredible size means that Betelgeuse releases extreme amounts of infrared and radiation. As a result, Betelgeuse likely outshines the Sun by at least 50 000 times. As a matter of fact, if we could see in all wavelengths of electromagnetic radiation, Betelgeuse would by far be the brightest star in the night sky.
The other aspect that makes Betelgeuse’s mass tricky to know precisely is the high rates of mass loss typical to massive stars. Such stars are likely to lose about a solar mass every 10 000 years.
Betelgeuse Temperature
Betelgeuse has a surprisingly cool surface temperature for such a massive star emitting great quantities of energy. Betelgeuse’s surface temperature is even cooler than the Sun’s. The red supergiant has a surface temperature of only 3590 °K, which is approximately 3316°C. The Sun, on the other hand, has a surface temperature of around 5778 °K, or 5504°C. Betelgeuse is therefore said to be intrinsically bright.
A Giant Variable Star
An extraordinary star all round, Betelgeuse is also a variable star. The star’s brightness ranges between approximately 0.0 and 1.3 in apparent magnitude. There are times when it is so bright it outshines Rigel to become the brightest star in Orion, and the sixth brightest star overall. At times it is even brighter than the magnitude 0.08 star Capella in the constellation Auriga. The star’s changing brightness means that it can also fade into seeming obscurity. At its faintest magnitudes, Betelgeuse may be dimmer than the stars Deneb (in the constellation Cygnus) and Beta Crucis (a binary star in Crux) to become the 20th brightest star visible from Earth.
Betelgeuse’s Big Size
So just how big is Betelgeuse in terms of its radius? For a better idea of the grand scale of the supergiant, let’s start with a comparison of the planets and our Sun.
- Mercury < Mars < Venus < Earth
- Earth < Neptune < Uranus < Saturn < Jupiter
- Jupiter < Proxima Centuari < Sun < Sirius A
- Sirius A < Pollux < Arcturus < Aldebaran
- Aldebaran < Rigel A < Antares < Betelgeuse
That is quite a remarkable scale, but to top it all off, Betelgeuse is the on the lower end of the most giant stars:
- Betelgeuse < Mu Cephei < VV Cephei A < VY Canis Majoris.
You may wonder how big Betelgeuse is compared to other stars in terms of mass. The upper limit of what Betelgeuse’s mass may be currently is 21 solar masses. The most massive star we know of, R136a1, is 315 solar masses. Betelgeuse doesn’t even make the list for most massive stars!
You can also get an idea for just how large Betelgeuse is by imagining the red supergiant at the center of the Solar System in place of the Sun. If this were so, Betelgeuse’s surface would extend past the asteroid belt, swallowing up the orbits of Mercury, Venus, Earth, Mars, and possibly Jupiter.
Betelgeuse had the honor of becoming the first star apart from the Sun to have the angular size of its photosphere measured in 1920. In terms of angular size as measured from Earth, Betelgeuse had the distinction of the largest angular diameter of any star seen in the sky apart from the Sun. However, R Doradus – a red giant variable star in the constellation Dorado – took that title in 1997. R Doradus is not as sizable as Betelgeuse in true measurements but does lie closer to our planet, at only 200 light years from Earth.
Life Cycle of Betelgeuse
Betelgeuse is estimated to have formed roughly 10 million – 12 million years ago. It is very young compared to stars like the Sun which is about 4.5 billion years old. However, Betelgeuse has always been in a different class of stars from the Sun. While the Sun is at the midpoint of its stellar cycle, the ‘young’ Betelgeuse is already at the end of its life.
Betelgeuse is a large, luminous and cool star classified as an M1-2 Ia-ab red supergiant. In professional astronomer, Betelgeuse is classified as an M1-2 Ia-ab red supergiant. The “M” in this designation shows that Betelgeuse belongs to a spectral class of stars that have a relatively low photosphere temperature. The star’s designation also shows that it is a supergiant with intermediate luminosity. Betelgeuse is often used as an anchor point by which other such stars are classified.
Being a large massive star comes at a great price. Betelgeuse has to burn through its hydrogen fuel far more quickly to support its great weight than less massive stars. The result is that large stars like Betelgeuse live and die quickly. All stars go through a stage when they are found along a distinct band on the Hertzsprung-Russell diagram called the main sequence. Stars on the main sequence are fusing hydrogen at their cores. Betelgeuse has long surpassed the main sequence of its life. The star has rapidly evolved into a larger and cooler star called a red supergiant.
A main sequence star is in a state of equilibrium, where the thermal energy of nuclear reactions in the core versus the gravity of the star balances out. Betelgeuse has exhausted its supply of hydrogen which decreases the thermal energy and gives gravity a chance to win the tug of war. Gravity starts crushing the star and the core contracts under the enormous weight, becoming hotter and denser. These intense contractions turn the interior of the star into a volatile place which is hot enough to start fusing the helium in the core into carbon and oxygen.
A chain effect then occurs. The fusing helium in the core heats the hydrogen surrounding the core sufficiently enough to start fusing into helium. Together, the helium fusing core and the hydrogen burning shell cause the outer envelope of the star to expand and cool. The internal reactions carry on in much the same way. The star gets hotter and hotter, able to fuse progressively heavier elements. A star like Betelgeuse will be able to fuse neon, magnesium, silicon, and finally iron before it can no longer maintain its chaotic existence. It is at this point that the star collapses and explodes in a dramatic supernova.
Will Betelgeuse Explode in a Supernova?
As we have seen, when a star gets older it quickly burns out its supply of hydrogen and then resorts to fusing helium and other elements. Betelgeuse will steadily expand and cool throughout this stage in its stellar evolution, fusing heavier and heavier elements until it has a core of iron. It is at this point that a massive enough star collapses on itself and explodes as a supernova.
Supernovae occur in different types: type I supernovae and type II supernovae. Type I supernovae occur within binary star systems. Type II supernovae are caused by the collapse of a massive star. Betelgeuse will produce a type II supernova.
They are absolutely the astounding events they are made out to be, but with a few small differences from science fiction movies: supernovae happen quickly and quietly and are remote and rare. We have recorded several supernovae throughout our universe, but only 1 or 2 happen within the Milky Way every century.
It is possible that Betelgeuse has already gone supernova. Even if the event happened recently we would only see it in a few hundred years from now, due to Betelgeuse being about 640.5 light years away. Of course, the star may have even gone supernova over 600 years ago, and will flare up dramatically any day now! On the other hand, there is also the chance that the red supergiant will continue to live for hundreds of thousands of years, and maybe even a million or more before dying.
Seeing the ghost of Betelgeuse’s violent explosion will be a sight to remember. The blast of the supernova will cause the star to appear as bright as the full Moon, with the chance that it may outshine even our closest neighbor. At its peak, it may reach a magnitude of -12.4, definitely bright enough to be remarkably obvious during the day. The star will remain at a constant brightness for about 3 months thereafter. Eventually, the star fades almost as quickly as it brightens, and over time will no longer be visible in the sky. What we will not see with our eyes is the small but incredibly dense stellar remnant left behind. Betelgeuse will either leave a neutron star or black hole behind following its supernova. Predictions show that it will likely be a neutron star of about 1.5 solar masses.
Supernova events can be fatal to any life on planets near the exploding star. Extreme amounts of high energy are released in the blast, and any planets in the vicinity will be bathed in radiation, if not blown to smithereens.
Should we be worried about Betelgeuse exploding and destroying life on Earth? Thankfully not. A star would have to be within 25 – 50 light years of a world for the planet and its life to be in danger. The star’s great distance means that we will be safe from Betelgeuse when does explode. The event will be no less thrilling to witness and will provide astronomers with a nearby supernova to study, without worrying about any adverse effects the blast may have on Earthlings.
Conclusion
Betelgeuse is a massive star host to massive mysteries. Studying the red supergiant will reveal many details regarding stellar evolution and the study of massive stars. The chance to view a supernova located as closely as Betelgeuse also provides astronomers with a rare opportunity to study these catastrophic events in greater detail.
With all the Betelgeuse star facts firmly in place, all that is left to do is go out on a dark night and observe the red supergiant with the awe it commands.