Rigel Star Facts

The hunter constellation Orion heralds the changing of seasons across the globe. As it rises, so does one of the brightest stars in the sky: Rigel. The blue-white gem is in stark contrast to Orion’s other famous star, the red-orange Betelgeuse. At magnitude 0.12, Rigel is the brightest star in Orion, but Betelgeuse sometimes does outshine it because Rigel is a semi-regular variable star.

Orion Stars

Rigel can be seen in the northern hemisphere from late autumn to early spring and is a fixture of the summer months in the southern hemisphere. Rigel is located on the celestial equator, so it is clearly visible for extended periods in both hemispheres and can be seen from all the world’s oceans and seas, barring the region within 8 degrees of the North Pole. As such, Rigel has always been an important star in navigation and is very easy to observe with binoculars and small telescopes.

Rigel also forms part of the Winter Hexagon or Winter Circle; an asterism outlined by the stars Rigel, Aldebaran, Capella, Pollux, Procyon, and Sirius. The asterism is best viewed from the northern hemisphere.

Rigel: Etymology and Designation

The original Arabic name that Rigel is derived from is Rijl Jauzah al Yusrā, meaning ‘the left leg or foot of the Great One [Orion]’. This ancient mention of the star dates back to at least the 10th Century. Other obsolete Arabic names for the star include Rigl al-Gabbar, and the similar names Algebar and Elgebar. The first record of the anglicized name Rigel dates back to 1252 in the Alfonsine Tables: a collection of astronomical data that was used to calculate the position of the Sun, Moon, and planets.

Johann Bayer designated Rigel ‘β Orionis’ or ‘Beta Orionis’ in 1603. Stars designated ‘beta’ are usually the 2nd brightest star of their constellation. For this reason, modern astronomers believe that Johann Bayer observed Rigel and Betelgeuse during a rare period in which Betelgeuse outshone Rigel – a result of both stars’ variability. This would explain his designations of Betelgeuse as Alpha Orionis and Rigel as Beta Orionis.

Rigel is an officially recognized star name and is included in the International Astronomical Unions’ Catalog of Star Names.

Rigel’s Significance in Ancient Cultures

Since Rigel is generally the 7th brightest star in the sky, and because of its location in Orion and proximity to other prominent constellations and stars such as Taurus and Sirius, Rigel has significance to many cultures throughout history.

  • The Wotjobaluk Koori tribesmen of south-western Australia named the star Yerrerdet-kurrk. The legend goes that Rigel was the mother-in-law of Totyerguil, the star we know as Altair. Due the seemingly close proximity of the stars, their stories warned of a man getting too close to his mother-in-law.
  • The Wardaman people of northern Australia called Rigel Unumburrgu, the mythical Red Kangaroo Chief. To them, Rigel was the head of all ceremonies when Orion was high in the sky. Betelgeuse was known as Ya-jungin or ‘Owl Eye Flickering’, a helpful aid who carefully watched over all proceedings.
  • New Zealand’s native Māori also linked Rigel to a leader, but this time as Puanga; daughter of the chief of all stars Antares (which they call Rehua). Several native groups of New Zealand marked the New Year with the sighting of Rigel.
  • It is safe to say that to most modern and western observers, Orion is known as the mythological Greek huntsman. The Greeks saw Rigel as the hunter’s knee or foot; and the nearby star Beta Eridani (in the constellation Eridanus) was Orion’s footstool.
  • Rigel and Betelgeuse represented two great but opposing families in Japanese culture. The stories go that the two stars symbolically grappled in the sky while the powerful families were locked in the Genpei War.
  • In other lore and cultures, Rigel’s connotation wasn’t as regal. Rigel is the star called “Aurvandil’s toe” in Norse mythology. The Lancandon people of southern Mexico called Rigel a little woodpecker, and on a darker note, Rigel represented the severed leg of the mythical hero Trois Rois (translating to three kings, or Orion’s belt) in the Caribbean.

Rigel in Modern Culture

There a few significant modern inventions and discoveries which have been named after the star Rigel:

  • A ship built in Copenhagen in 1924 was called MS Rigel. The ship sunk carrying prisoners in 1944. There were also two US Navy Ships called USS Rigel.
  • A cancelled cruise missile program of the US Navy was titled SSM-N-6 Rigel.
  • There is a small group of Islands surrounding Antarctica named Rigel Skerries. Mount Rigel is also in Antarctica.

How Far is Rigel from Earth?

Like the Solar System, Rigel is located in the Milky Way Galaxy. There are different ways to calculate how far Rigel is from Earth, so the star’s true distance from the Sun remains somewhat uncertain; differing depending on the method used to get the estimate. Some calculations show Rigel to be 863 light-years or 265 parsecs away from the Solar System. This estimate has a margin of error around 9%.

We may also take the estimated distance of a companion star to Rigel, resulting in a distance of 1,100 light-years or 340 parsecs from Earth. This method is problematic as the measurements for the companion are unreliable.

Another route in finding Rigel’s distance from the Sun is working around the distance of the Orion OB1 Association: a very loose group of stars which form part of the constellation. Rigel is one of these stars, lying on the outskirts of the stellar association. The association as a whole is up to 1,600 light-years or 500 parsecs from the Sun. Rigel also belongs to the Taurus-Orion R1 Association, a larger but more a loosely-defined collection of stars. This cluster is closer to Earth than the OB1 Association, lying at 1,200 light-years or 360 parsecs away.  Astronomers believe that Rigel is much closer to the Earth than the majority of stars in the Orion OB1 Association and the Orion Nebula.

Rigel also lies quite close to our line of sight of the Orion Nebula, so the star is often associated with it. In reality, the Orion Nebula is almost twice as far from the Sun as Rigel.

Rigel Temperature, Color and Size

Rigel is a young, hot and massive star. It has a mass of 21 Solar Masses, and may even be as massive as 24 Solar Masses. Rigel’s radius is more than 70 times that of the Sun.

Even though Rigel may be heading toward the final stages of its stellar lifecycle, it is very young relative to other stars, including our own. While the Sun is approximately 4.6 billion years old, and only halfway through its life, Rigel is only about 7 – 9 million years old.

Rigel is a blue supergiant star, a type of star which is not the norm in the Milky Way. Owing to how relatively uncommon these types of stars are and the uncertainty in measuring their distances from the Sun, it is considerably difficult to draw accurate conclusions on their physical characteristics. Most of what we understand about Rigel’s properties are taken from theoretical models of a star’s evolution.

For one, Rigel’s true amount of energy output is not well understood, though it is often considered the most luminous star within 1,000 light years of the Sun. Some models suggest that Rigel is approximately 120,000 more luminous than the Sun. The full range of theorized luminosity spans from at least 61,500 more luminous than the Sun to as high as 363,000 times more luminous than our own star.

Astronomers can draw conclusions on a star’s temperature by its spectral type and color. Rigel’s blue-white color indicates that it is an extremely hot star. Rigel’s surface temperature is estimated to be about 12,100 K (11,727 C or 21,140 F) – almost double that of the Sun’s surface temperature.

Rigel Facts: Life Cycle and Multi-Star System

Rigel appears as a single brilliant point of light to the unaided eye, but professional observations reveal it belongs to a multi-star system containing at least four stars that we know of: Rigel A, Rigel Ba, Rigel Bb, and Rigel C. The name Rigel is specifically used to refer to the primary star of the system, Rigel A, though it has also been used to describe the entire system. Rigel’s companion appears to be a triple star system, which as a whole is referred to as Rigel B.

Rigel A is a blue supergiant star which formed about 7 to 9 million years ago. Though it is very young compared to the Sun, it has already exhausted its supply of hydrogen in its core. Stars expand and become cooler as they age and move away from the main sequence of the Hertzsprung–Russell diagram. At 12,000 K, an aging Rigel is still much hotter than the Sun. During the prime of its cycle, a star like Rigel could reach temperatures of around 30,000 K.

Stars as massive as Rigel certainly have their own unique curve in stellar evolution. Astronomers believe that Rigel may have already passed through a red supergiant phase and was much cooler than it is currently. The star then increased in temperature and became a blue supergiant for a second time round. Through all of these changes, Rigel has probably lost around 3 Solar Masses compared to the mass it once had during its main sequence.

Supergiant stars like Rigel also have some of the most astounding and cataclysmic deaths in the cosmos. Rigel is expected to eventually end its stellar life as a Type II supernova. The star will rapidly collapse on itself as it can no longer support its great weight, and this will trigger a massive explosion. Rigel has the potential to be one of the closest supernovas to Earth, but will not pose any threat to life on the planet. Instead, observers at the time will be treated to a brilliant display: a star of magnitude -11, as bright as a quarter Moon.

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