Interesting Facts About the Star Betelgeuse
Betelgeuse is a red supergiant star. It is one of the largest stars we can see with the naked eye. Also, its reddish color makes it stand out in the night sky in the constellation of Orion. Let’s take a look at some more facts about the Betelgeuse star before diving into the detail!
- Betelgeuse is designated Alpha Orionis (α Ori) in the Bayer designation. The Alpha designation is usually given to the brightest star in the constellation, but Betelgeuse is only the 2nd-brightest in Orion after Rigel.
- Betelgeuse is a variable star with an apparent brightness that varies from +0.0 to +1.6. This makes it the second brightest star in Orion and the 10th brightest star in the night sky.
- The star Betelgeuse is only 10 million years old. This is considered young in terms of star age. However, about 100,000 from now, this evolved and massive star is expected to reach the last stages of its life and become a supernova.
- Betelgeuse has a radius that is about 764 times that of the Sun. With this size, if it were to replace our Sun in the solar system, this star would reach past the asteroid belt and even beyond Jupiter. This means that it would engulf the terrestrial planets—Mercury, Venus, Earth, and Mars.
- Betelgeuse is 16.5 times as massive as the Sun. This supergiant has 126,000 solar luminosities, making it look bright at 548 light-years away. This star has a surface temperature of 3,600 K which means it is cooler than the Sun.
- Only about 13% of Betelgeuse’s radiant energy is in the form of visible light. If our eyes were able to detect radiation in all wavelengths, then Betelgeuse would take the place of Sirius as the brightest star in our night sky.
- Betelgeuse is losing about one solar mass every 10,000 years. The star spews out this material unevenly in all directions, forming a nebula around the red star.
- The cloud of matter that surrounds Betelgeuse is 250 times the size of this star. Also, this nebula is said to extend about 30 astronomical units (AU) or 30 times the Sun-Earth distance. In the solar system, this equals the distance between the Sun and the farthest planet, Neptune.
- The red supergiant Betelgeuse is part of the Winter Triangle asterism. Together with it are some of the brightest stars in the sky—Sirius from Canis Major and Procyon from Canis Minor.
The Betelgeuse Star (α Orionis)
- Color: Red (M-type)
- Spectral type: M1-2
- Apparent magnitude: 0.0 to 1.6
- Mass: 16.5 solar masses
- Radius: 764 solar radii
- Luminosity: 126,000 Suns
- Surface temperature: 3,600 K
- Constellation: Orion the Hunter
- Distance: 548 light-years from the Sun
Betelgeuse is a red supergiant star that marks the right shoulder of Orion. It is a variable star with an apparent magnitude that changes between 0.0 to 1.6. Though it is only second to Rigel as the brightest star in the constellation, it is designated Alpha Orionis in the Bayer system.
Because of its variability, Betelgeuse sometimes outshines Rigel. This must be the case when Johann Bayer published the Uranometria in 1603, where Betelgeuse became known as Alpha Orionis and Rigel is Beta Orionis.
Betelgeuse is a single star and it does not belong to any star system. Also, it is considered a runaway star since it is not part of any star-forming region.
The star Betelgeuse has roughly 764 times the Sun’s radius and is also 16.5 times as massive. As a red giant, it shines with the luminosity of 126,000 Suns combined. This is why, even if it is 548 light-years away, it is still very bright as seen on Earth. Though it is larger, the star’s surface temperature is only 3,600K, which means it is cooler than the Sun (5,778 K).
While the Sun is 4.6 billion years old, Betelgeuse is only about 10 million years old. Though it is much younger, Betelgeuse is already an evolved star. A star this massive would need a very large amount of energy to keep it going. This is why it will consume its fuel faster than the Sun.
In 2009, the European Southern Observatory (ESO)’s Very Large Telescope (VLT) in Chile released an image of Betelgeuse with a cloud of dust surrounding it.
Since it is very massive, Betelgeuse will likely collapse into itself and end its stellar life as a supernova. This explosion is projected to happen in the next 100,000 years or so. After it sheds its outer layers, it will leave behind a neutron star or a black hole.
Why Betelgeuse Became Dimmer in 2019
In late 2019, changes were observed in the Betelgeuse star as it noticeably became dimmer. Its apparent magnitude dropped to 1.7 from 0.5. This drop came to a halt in early 2020 when the red supergiant started to regain its brightness.
This mysterious event made some people think that the star may be about to explode. Astronomer Miguel Montargès and his team used the VLT to understand why this happened to Betelgeuse. According to them, there are two reasons for this.
The first was that the large convective cells of the star caused hot and cold spots on its surface. The other reason for the great dimming episode was a cloud of dust that blocked the starlight from our point of view. This cloud also originated from Betelgeuse itself.
The exact time when Betelgeuse will explode is still unknown. However, since it is relatively close to us in a stellar sense, the supernova explosion would be visible on Earth even during the daytime.
Thankfully, this great blast of matter will not affect Earth since it is more than 500 light-years away. According to astrophysicists, a supernova would have to be around 50 light-years away from Earth for it to affect us.
In 2021, the red hypergiant VY Canis Majoris also showed some great dimming episodes like Betelgeuse. According to NASA’s Hubble Space Telescope, the reason behind this was just like the dimming of Betelgeuse. However, it was just happening on a much larger scale.
What’s in a Name?
Many of the unique star names were derived from translations and misreadings of the foreign names of stars. The name “Betelgeuse” is one of such.
In Arabic, the constellation of Orion was called Jauza or Jauzah. And from this, Betelgeuse was called Yad al-Jauzā which means “the hand of al-Jauzā.” During the 13th century, the “ya” in the Arabic name became “ba,” and this error caught on.
From that, the European name “Betelgeuse” was born, which is popularly pronounced as “beetle juice.”
Orion Constellation (The Hunter)
The hourglass shape of Orion the Hunter is one of the easiest constellations to identify. Since it is located in the celestial equator, observers from all around the globe can see it in the night sky. The conspicuous sky pattern of the celestial hunter has been known from ancient times.
Since it is visible from almost anywhere on Earth, it has become a part of different mythologies across cultures. The Babylonians called it “The Heavenly Shepherd” while the Armenians called it “Hayk.” Also, the stars of Orion were considered as the god “Sah” by ancient Egyptians.
Today, the most famous association of Orion is that of a gigantic hunter in Greek mythology.
Looking at the sky, we can see several asterisms inside the constellation of Orion. Completing the form of the celestial hunter are its Belt, Shield, Sword, and Club. Aside from these asterisms, Orion is also made up of some of the brightest stars in the sky.
The brightest star in the constellation, Rigel, is also the 7th brightest star in the sky. The 2nd and the 3rd brightest in the constellation, Betelgeuse and Bellatrix, are also the 10th and 25th brightest stars in our night sky.
The most famous deep-sky object in the Orion constellation is Messier 42 or the Orion Nebula. The reddish glow of this object can be easily seen with the naked eye. It is also part of Orion’s Sword asterism. The Trapezium open cluster is located at the center of this diffuse nebula.
Asterisms in the Constellation of Orion
Asterisms are different from constellations. While constellations are interpreted as sky patterns, they also have specific areas and boundaries set by the International Astronomical Union (IAU).
Meanwhile, asterisms are sky patterns formed by connecting the stars in a constellation or with the stars of other constellations.
| Name of Asterism | Members of the Asterism |
|---|---|
| Orion’s Head | * Meissa (Lambda Orionis) |
| * Phi-1 Orionis | |
| * Phi-2 Orionis | |
| Orion’s Club | * Mu Orionis (*Orion’s elbow) |
| * Nu Orionis | |
| * Xi Orionis | |
| * Chi1 Orionis | |
| * Chi2 Orionis | |
| Orion’s Belt | * Alnitak (Zeta Orionis) |
| * Alnilam (Epsilon Orionis) | |
| * Mintaka (Delta Orionis) | |
| Orion’s Sword | * Theta Orionis |
| * Iota Orionis | |
| * 42 Orionis | |
| * Orion Nebula (Messier 42) | |
| * De Mairan’s Nebula | |
| * Running Man Nebula | |
| Orion’s Shield | * Pi1 Orionis |
| * Pi2 Orionis | |
| * Pi3 Orionis | |
| * Pi4 Orionis | |
| * Pi5 Orionis | |
| * Pi6 Orionis |
Betelgeuse Star in the Winter Triangle
The Winter Triangle is an asterism made up of three stars from different constellations. Forming the three vertices are the stars:
- Betelgeuse
- Sirius
- Procyon
As the name says, this sky pattern is most prominent during winter in the northern hemisphere. Together with Betelgeuse are Sirius and Procyon, the brightest stars in the constellation of Canis Major and Canis Minor. It is also important to note that the −1.46 magnitude Sirius is the brightest star in our night sky.
The Winter Triangle is inside the bigger Winter Hexagon or Winter Circle—an asterism that is made up of the stars Rigel (Orion), Aldebaran (Taurus), Capella (Auriga), Pollux (Gemini), Procyon (Canis Minor), and Sirius (Canis Major).
Using Betelgeuse to Find Other Stars
Since Orion is one of the easiest constellations to spot, many use it as a navigational aid to find other objects in the night sky.
For example, if draw an imaginary line connecting the three stars of Orion’s Belt and extend it upwards, we will be pointed to Aldebaran, the brightest star in the Taurus constellation. From there, we will then be able to locate the Pleiades.
Similarly, we can use Betelgeuse as a guide to finding other stars. By connecting Rigel and Betelgeuse, and extending it past the red supergiant, we will be pointed to Castor and Pollux. These two are the brightest stars in the constellation of Gemini.
Where Can You See Betelgeuse in the Night Sky?
Betelgeuse is one of the easiest stars to spot in the night sky. A big part of this is because of its unmistakable bright red color. Its coordinates are indicated below:
- Right Ascension: 05h 55m 10.3s
- Declination: +07° 24′ 25.4″
Another reason why Betelgeuse is easy to locate is its position in the Orion constellation. Orion is surrounded by the constellations of Gemini, Taurus, Eridanus, Lepus, and Monoceros.
Once you find Orion, the red star that marks the shoulder or armpit of the celestial hunter is Betelgeuse. In the constellation’s sky pattern, it lies above the star Alnitak, which is a part of Orion’s Belt.
How and When to Find Betelgeuse Star?
The best time to see the star Betelgeuse depends on where you are. In the northern hemisphere, the best time to see it is during winter, from around January to April.
In January and February, Betelgeuse rises just as the Sun is dipping into the horizon. This time, it is summer in the southern hemisphere.
Though it is not part of the Winter Hexagon (Winter Circle), Betelgeuse lies at the center of this asterism. This is another way of locating this giant star.
Betelgeuse in History and Mythology
The name Betelgeuse was derived from Arabic which relates to the “shoulder” or “armpit” of the giant/hunter. While there is no single tale that explicitly tells us the mythology of this star, there are some interesting stories that surround it.
According to a myth in the Americas, the red star Betelgeuse marks the wound of the warrior Orion.
Aboriginal people in South Australia have an oral tale about the variable nature of Betelgeuse.
In this story, there was a hunter called Nyeeruna (Orion) who pursued the Yugarilya (the Pleiades). The Yugarilya was protected by their older sister, Kambugudha (the Hyades).
Nyeeruna was mocked by Kambugudha. The hunter was ready to attack Kambugudha so he readied his right hand (Betelgeuse). As he lifted his hand, it filled with “fire magic.” However, Kambugudha was also quick to lift her foot (Aldebaran) which also had fire magic. She kicked dust into Nyeeruna and caused his magic to fade.
To Kambugudha’s dismay, Nyeeruna’s magic revived more quickly than hers and the hunter went after the sisters once again.
Interpreters of the lore noted that the “fire magic” in the story talked about the variability of the stars Betelgeuse and Aldebaran. This is true since Betelgeuse makes roughly four cycles every time Aldebaran makes one.
According to Stephen R. Wilk, Orion could be Pelops from Greek mythology.
In the story, Pelops was killed by his father King Tantalus. The king made Pelop’s flesh into a stew and offered it to the gods of Olympus. The gods did not accept the offering as they sensed something was not right.
However, the grief-stricken Demeter, whose daughter was just abducted, ate the boy’s shoulder in the stew. The other gods stopped the savage banquet and banished Tantalus. They reassembled Pelops and gave him life again. Hephaestus replaces his lost shoulder with one that is made of ivory. This ivory shoulder is said to be the star Betelgeuse.
Orion Mythology
In Greek mythology, Orion was known as a skilled and gigantic huntsman who boasted that he would kill all animals on the planet. The goddess of Earth, Gaia, heard this and became angry at the hunter.
With this, the goddess ordered a scorpion to go after Orion. The hunter was severed by the scorpion. Their rivalry never ended even as they were put in the sky as constellations. While Orion rises during winter, Scorpius becomes more prominent in the summer. These two constellations never meet in the night sky.
Sources:
(https://earthsky.org/brightest-stars/betelgeuse-will-explode-someday/)
(https://skyandtelescope.org/astronomy-news/aboriginal-australians-observed-red-giant-variability/)
https://www.nature.com/articles/d41586-021-01633-4
https://en.wikipedia.org/wiki/Betelgeuse
https://en.wikipedia.org/wiki/Orion_(constellation)
https://adsabs.harvard.edu/full/1999JAVSO..27..171W
https://www.nasa.gov/feature/goddard/2021/hubble-solves-mystery-of-monster-stars-dimming
https://www.bbc.com/news/science-environment-57501416
Image Sources:
The Betelgeuse Star (α Orionis: https://upload.wikimedia.org/wikipedia/commons/thumb/5/57/Betelgeuse_captured_by_ALMA.jpg/800px-Betelgeuse_captured_by_ALMA.jpg
Why Betelgeuse Became Dimmer in 2019: Image by Andrea Dupree (Harvard-Smithsonian CfA), Ronald Gilliland (STScI), NASA, and ESA; https://cdn.britannica.com/75/137075-050-57D0ACFA/Betelgeuse-ultraviolet-light-Hubble-Space-Telescope.jpg
Orion Constellation (The Hunter): https://upload.wikimedia.org/wikipedia/commons/thumb/f/ff/Orion_IAU.svg/800px-Orion_IAU.svg.png
Asterisms in the Constellation of Orion : https://upload.wikimedia.org/wikipedia/commons/thumb/a/ab/Orion_%28constellation%29_Art.svg/800px-Orion_%28constellation%29_Art.svg.png
Betelgeuse in the Winter Triangle: https://upload.wikimedia.org/wikipedia/commons/thumb/b/b1/Hubble_heic0206j.jpg/1024px-Hubble_heic0206j.jpg
Using Betelgeuse to Find Other Stars: https://upload.wikimedia.org/wikipedia/commons/thumb/9/9f/Orion-guide_dark.svg/800px-Orion-guide_dark.svg.png
Where Can You See Betelgeuse in the Night Sky?: https://stellarium-web.org/
How and When to Find Betelgeuse?: https://upload.wikimedia.org/wikipedia/commons/thumb/a/ad/Winter_Hexagon_and_Great_Southern_Triangle_%28Stellarium%29.png/1024px-Winter_Hexagon_and_Great_Southern_Triangle_%28Stellarium%29.png
Betelgeuse in History and Mythology: https://upload.wikimedia.org/wikipedia/commons/thumb/c/ca/Aratea_58v.jpg/800px-Aratea_58v.jpg