Rigel: Orion's Brightest Star

rigel, witch head nebula
Light from the star Rigel reflects off the dust composing the Witch Head Nebula.
(Image: © Rogelio Bernal Andreo / NASA)

Rigel is a blue supergiant that is the brightest star in the constellation Orion (the Hunter). The star is only 10 million years old, compared to the sun's 4.5 billion, and due to its measured size and brightness it is expected to end in a supernova one day. It also has two known companions, Rigel B and Rigel C.

The star is variable and is considered an Alpha Cygni-type star. (Alpha Cygni is the scientific name for Deneb, the prototype star for this kind of variability.) Its luminosity is so bright that it shines and scatters in an adjacent nebula, called the Witch Head Nebula,which is about 40 Earth-sun distances or astronomical units away.

In science fiction, Rigel's name is on a a number of planets in the "Star Trek" universe, is mentioned in "The Hitchhiker's Guide to the Galaxy," and also features in a number of novels, computer games and comic books.

Rigel before modern astronomy

Rigel's name comes from an Arabic phrase, Rijl Jauzah al Yusrāʽ. It means "the left leg of the Jauzah," according to Richard Hinckley Allen's "Star Names: Their Lore and Meaning." It is also sometimes translated as "the left leg of the giant," reportedly referring to the constellation Orion, of which Rigel forms a part. Rigel is more properly known as Beta Orionis.

Scandinavian folklore said that Rigel indicated one of the large toes of Orwandil; the thunder god Thor broke off the other toe when it was frost-bitten, according to a report recorded by Allen.

In Japanese culture, Rigel is sometimes called Genji Boshi and a bright red star in Orion — Betelgeuse — has the name of Heike Boshi. Those names hearken back to the Heian era (794-1192) in Japan, according to an online account by Steve Renshaw and Saori Ihara. (A later version of the account was published in the "Kyoto Journal" in 2000.)

"The legendary war that brought the somewhat artistic and gentle Heian era to a close took place between the Taira (Heike) and Minamoto (Genji) families," the authors wrote.

"The colors of Taira were red, and the colors of the Minamoto family were white. Ultimately, the Minamoto (Rigel) family won the war and moved the capital to Kamakura, ushering in an era of Samurai warriors and leading to centuries of little true peace ... These two bright stars of red and white still do battle with the steepes of the belt holding them apart."

Locating Rigel

Rigel is today known as a class B supergiant. It's close to zero magnitude in Earth's sky, making it a bright star. But Rigel is also intrinsically luminous, shining with the equivalent light of 85,000 suns, according to astronomer Jim Kaler. Its radius is 73 times that of the sun. Rigel's location is:

  • Right ascension: 5 hours 14 minute 32.3 seconds
  • Declination: -8 degrees 12 minutes 6 seconds

Rigel to astronomers

Astronomers believe the star is about 10 million years old and that later in its life, it will likely transform into a red supergiant (just like Betelgeuse) and eventually explode into a supernova, Kaler added.

"If and when it does go, it would appear to us as bright as a quarter moon," Kaler wrote.

Rigel also has two distant stellar companions, Rigel B and Rigel C – a binary system. At the ninth magnitude, the combined light of these stars would usually be enough for most telescopes to pick up, but they are too close to the bright Rigel to be easily visible.

Rigel's bright starlight also bounces off a nearby nebula, as shown in a picture published in 2012 on NASA's Astronomy Picture of the Day website.

"The blue color of the Witch Head Nebula and of the dust surrounding Rigel is caused not only by Rigel's intense blue starlight, but because the dust grains scatter blue light more efficiently than red," NASA wrote. "The same physical process causes Earth's daytime sky to appear blue, although the scatterers in Earth's atmosphere are molecules of nitrogen and oxygen."

Astronomers have made several observations of Rigel in recent years. Examples include:

  • A 2014 study looking at the variability of stellar winds coming from Rigel, over several years. The astronomers noted that the observations were made in high spatial and spectral resolution. 
  • A 2017 study measuring the stellar flux density of Rigel, Aldebaran and Fomalhaut. Stellar flux refers to how much radiation energy a star emits. In general, the group found that stellar flux density is at a minimum at the outer surface of a star and at a maximum inside of the star.
  • Rigel is also used as an example of how massive stars may evolve, as discussed in this 2013 paper published by the European Astronomical Society, and this one from 2014 published in Proceedings of the International Astronomical Union.

Rigel in science fiction

The name "Rigel" is a popular planetary name in "Star Trek," with references to it popping up in multiple versions of the series. The earliest mention of it was in the original 1960s-era pilot, "The Cage", which referred to Rigel VII. Although that episode did not actually air until the 1980s, Rigel VII and much of the footage from 'The Cage" was used in the two-part episode, "The Menagerie."

A few other uses of Rigel:

  • In Douglas Adams' "The Hitchhiker's Guide to the Galaxy," Rigel (presumably it is Rigel, as the name "Orion Beta" is used) was the site of madranite mining belts.
  • Several computer games of the 1980s and 1990s, such as "Rescue at Rigel," "Rigel's Revenge" and "Duke Nukem II."
  • A Season 2 episode of "The Simpsons," "Hungry Are the Damned", where the family is temporarily kidnapped by a couple of aliens from Rigel IV.
  • In comic book series such as "Justice League," "Thor," "Transformers" and "Monty."

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