Betelgeuse Star

The mysteries of Betelgeuse

Betelgeuse is a star in the constellation Orion that is really quite mysterious, much of this due to the fact that it may be about to transform into a very rare event – a supernova. Only about 4 or 5 supernovae have been detected in the Milky Way Galaxy, and it is believed that they occur about every 50 to 100 years. In this article we will discuss Betelgeuse and the facts surrounding it, including why it may be about to turn into a supernova.

Observing Betelgeuse

Betelgeuse is easily visible in the night sky

Betelgeuse is a distinctly reddish star in the constellation Orion and is the ninth brightest star in the night sky which has a magnitude which varies between +0.0 and +1.3 since it is a semiregular variable star. This type of star is a giant or supergiant star of intermediate or late spectral type showing significant periodical changes in their light output as well as some irregularities. Betelgeuse is actually the brightest star in the night sky in the near infrared range of the light spectrum.

It is quite obvious then that Betelgeuse is easily observed in the night sky of the Northern Hemisphere, even with binoculars, although even a modest telescope will give some very good observational detail.

History Of Betelgeuse

What is the history of Betelgeuse?

The history of Betelgeuse goes back a long way, to ancient times. Claudius Ptolemy was a mathematician, astronomer, and astrologer who lived in Alexandria in the then Roman province of Egypt in the 2nd century A.D. He observed Betelgeuse and described it as having a sort of ‘ruddiness’. Going back even further, about 3 centuries before the time of Ptolemy, Chinese astronomers described Betelgeuse as having a yellow color, possibly indicative of it being in a yellow supergiant phase back then. In the nineteenth century numerous observations were made of Betelgeuse, some describing it as having an orange color.

Betelgeuse Facts

What are the facts about Betelgeuse?

Location & Distance

Betelgeuse, as mentioned previously, is located in the constellation Orion about 643 light-years from Earth within an error range of +/- 46 light-years. Previous estimates had placed it at a distance of about 430 light-years from Earth, but the high degree of variability in the brightness of Betelgeuse made accurate measurements difficult, and new research has given us the greater, more accurate figure.

Betelgeuse is considered to be a runaway star not associated with any star system – it is moving away from Orion’s Belt as an isolated star in interstellar space.


Betelgeuse is classified as a semiregular variable star, meaning that although there may be some periodicity noticed in the brightness changes, there will also be periods of irregular changes with varying amplitudes of brightness and cycles of different lengths. Betelgeuse is a pulsating red supergiant with amplitudes of up to one magnitude and a period variability of from tens to hundreds of days.

The supergiant red star Betelgeuse usually shows only small brightness changes to around magnitude +.5 although it has been known to become as bright as magnitude +0.0 or as faint as magnitude +1.3. It has a main period of about 400 days, with a secondary period of around 2100 days, although there is a significant amount of irregularity.

Size & Mass

Betelgeuse, being a supergiant red star, is absolutely huge – it’s angular diameter is estimated at between .042 and .069 arcseconds and the stellar disk of Betelgeuse is between 650 and 1000 times the diameter of the Sun, or somewhere around 560 million and 865 million miles – again it is difficult to be more accurate because of the significant variability of Betelgeuse. If Betelgeuse were at the center of our Solar System it would extend beyond the orbit of Jupiter(484 million miles) and approach that of the orbit of Saturn(934 million miles). An interesting fact is that Betelgeuse is known to have shrunk by about 15 percent since 1993, which confirms that it is a dying star which is about to go supernova.

Betelgeuse has an estimated mass of approximately 12 times that of the Sun, which would be in the range of about 50 nonillion pounds – 50 million trillion trillion pounds.


As we have already noted, Betelgeuse is a runaway and isolated star in interstellar space. The most likely possibility for the origin of Betelgeuse is the Orion OB1 Association, a group of several dozen hot giant stars and thousands of lower mass stars and protostars, from which it is believed to have formed around 12 million years ago. It then became a runaway star from this group of stars.

It is thought that Betelgeuse evolved unusually rapidly because of its high mass, eventually becoming the dying red supergiant star that we see today – although since it is around 643 light-years away we are seeing it about 643 years in the past, and it may well have already gone supernova.

Stellar Dynamics

Betelgeuse is in the late stage of it’s stellar evolution, possibly losing the equivalent of the mass of the Sun every 10000 years. There is still a great deal of uncertainty about the evolution of Betelgeuse – it is possible that it could go into a brief yellow supergiant phase and then explode as a blue supergiant or a Wolf-Rayet star(WR star) – a type of rare heterogeneous star with an unusual spectra emission.

Astronomers have observed a huge plume of gas about 6 times the radius of the stellar disk of Betelgeuse which indicates that the red supergiant is not shedding mass evenly in all directions, but in an irregular asymmetric way. It is also believed that a huge stellar disturbance is underway in Betelgeuse which caused this giant plume of gas since observations with the European Space Agency’s AMBER shows giant gas bubbles forming in the extended atmosphere of Betelgeuse as large as the stellar disk of Betelgeuse itself. This could possibly show that a supernova could be imminent, and indeed may have already occurred since Betelgeuse is about 643 light-years away and we are seeing it about 643 years in the past.

Other Facts

Betelgeuse can be seen in the constellation Orion, in the range of a magnitude +0.0 to +1.3 star, usually somewhere around magnitude +.5. It is in the evolutionary stage of a red supergiant with a spectral type of M1-M2. It is a SRc type of variable star with a U-B color index of +2.06 and a B-V color index of +1.85. Betelgeuse has a radial velocity of about 13.5 miles per second and is drifting in interstellar space at a velocity of about 18.6 miles per second. Also it is roughly about 630 light-years from Earth and has an absolute magnitude of about -5.85. The mass of Betelgeuse is just under 12 solar masses(about 11.6 + or – .5) and it has a radius of over 510 million miles, with a radial velocity of about 3.1 miles per second, although this is only a rough estimate because of the variability of Betelgeuse which makes accurate measurements almost impossible. Betelgeuse has a luminosity range of 90000 to 150000 radiant flux units which is the power emitted in the form of photons. Betelgeuse has a temperature of around 6000 degrees Fahrenheit(3590 degrees Kelvin) and is in the range of 8 – 8.5 million years old.

Life Cycle Of Betelgeuse

What is the life cycle of Betelgeuse?

Betelgeuse is in a class of red giant stars which are extremely large, the largest type of star known in the Universe, although not the most massive. Because they do have a very large mass, typically about 20 to 30 times that of the Sun, they have a very short lifespan(in stellar terms), usually around 25 million years.

They start our as a main sequence star like our sun with 20 – 30 solar masses fusing hydrogen into helium. Then after 5 – 20 million years they exhaust their hydrogen/helium fuel and eventually go into the carbon fusion stage in their core which causes their size to increase dramatically and they become a red supergiant star. Then in around a few million years they will suddenly collapse and become a supernova. It could go supernova in 100000 years or less – maybe it already has and we don’t know it yet because we are seeing it as it was about 643 years in the past.

After this it is predicted that Betelgeuse will become a neutron star, although it will not be massive enough to become a black hole or produce gamma ray bursts.

Betelgeuse Supernova

Betelgeuse may be about to go supernova

Betelgeuse is very close to going supernova in stellar terms, but that doesn’t necessarily mean within a few hundred years, although that is within the realm of possibility. There is a very high probability that this will occur within the next several million years.

Right now it has a mass estimated somewhere around 12 solar masses, although it likely had a mass of close to twice that much, 20 – 25 solar masses, when it was born. In the early stages Betelgeuse was a main sequence star, meaning that it was in the hydrogen fusion stage. It left that stage some time ago and is now in the carbon fusion stage(fusing helium to carbon), and a supernova event is imminent as discussed above.

A star with a mass similar to our Sun can expect to live somewhere around 10 billion years. Very massive stars like Betelgeuse have a much shorter lifespan, usually in the range of about 10 to 20 million years – the higher the initial mass the shorter the lifespan will be. Betelgeuse probably has around a thousand(or less) to a few million years before it goes supernova. Since it is roughly 630 light-years away, this may have already happened and we don’t know it yet since we are seeing Betelgeuse as it was about 630 years ago.

When Betelgeuse does go supernova it will be an unbelievably spectacular event – it will become as bright as the full moon for weeks, visible even in the daytime sky. Then after the supernova is over Betelgeuse will become a powerful neutron star at it’s core, although it probably won’t be powerful enough to emit gamma ray bursts.

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