Rigel is the brilliant blue-white star marking the foot of Orion. Although it appears as a single point of light in the night sky, this extraordinary star has plenty of surprises. Here are some interesting facts about Rigel.
Easy to Find in the Night Sky
Rigel is easy to find once you can identify Orion’s Belt, the distinctive row of three bright stars in the constellation’s center. From Northern Hemisphere locations, look below Orion’s Belt for the two bright stars marking Orion’s feet — Rigel is the brighter, blue-white star. From mid-northern latitudes, Rigel is prominent in the evening sky during winter, while Southern Hemisphere observers see Orion during their summer. Because Rigel lies close to the celestial equator, it can be seen from most inhabited parts of Earth and has also been used as an important navigational star. No telescope or binoculars are needed — Rigel is easily visible to the naked eye.
Brightest Star in Orion
Rigel is the brightest star in the constellation Orion and is generally listed as the seventh-brightest star in the night sky. Its name comes from an Arabic word meaning “foot,” referring to its position at Orion’s foot. Curiously, Rigel is designated Beta Orionis, while Betelgeuse is Alpha Orionis. When Johann Bayer assigned the names in 1603, Betelgeuse was apparently considered the brighter star, although its brightness varies considerably and today Rigel normally outshines it.
More Than 100,000 Times Brighter Than the Sun
Rigel lies around 860 light-years from Earth, yet despite this enormous distance it is still one of the brightest stars in our night sky. That’s because this blue supergiant produces more than 100,000 times as much light as the Sun, making it one of the most luminous stars visible to the naked eye. Rigel is also around 20 times more massive than the Sun, and it is this enormous mass that allows the star to generate energy at such a tremendous rate.
A Giant Blue-White Star
Rigel is a blue supergiant around 75 times the radius of the Sun, giving it a diameter of roughly 100 million kilometers (60 million miles). It is also about twice as hot as the Sun, with a surface temperature of around 12,000 K (21,000°F), which gives Rigel its distinctive blue-white color. By comparison, the much larger red supergiant Betelgeuse has a surface temperature of only around 3,500 K (5,800°F), producing a striking difference in color easily seen with the naked eye.
Just 8 Million Years Old
Rigel is only around 8 million years old, compared with about 4.6 billion years for the Sun. In other words, the Sun is more than 500 times older than Rigel, yet Rigel is already the more evolved star. Although massive stars have far more nuclear fuel available, they burn through it at a tremendous rate. Rigel has therefore already evolved off the main sequence to become a blue supergiant, while the Sun is still only about halfway through its roughly 10-billion-year main-sequence lifetime.
Destined to Explode as a Supernova
Rigel’s enormous mass also determines how its life will end. A star this massive has an immensely powerful gravitational pull, which is currently balanced by the outward pressure within the star. As Rigel ages, it will fuse progressively heavier elements in its core until it can no longer produce enough energy to support itself. Gravity will then take over and the core will collapse, triggering a supernova explosion and leaving behind a neutron star or possibly a black hole.
Actually a System of at Least Four Stars
The brilliant point of light we call Rigel is actually a system of at least four stars. The blue supergiant Rigel A is so luminous that it completely overwhelms its three much fainter companions, making the entire system appear as one star to the naked eye. Two of those companions, Rigel Ba and Rigel Bb, form a close binary pair, while Rigel C is another member of the system. What looks like a single blue-white star from Earth is therefore actually the combined light of an extraordinary four-star system.
Lights Up the Witch Head Nebula
Rigel is so luminous that its light illuminates the Witch Head Nebula, a vast cloud of interstellar dust. Known as IC 2118, the nebula stretches across roughly 50 light-years, with its dust reflecting and scattering Rigel’s blue light toward Earth. The result is an enormous ghostly blue cloud resembling the profile of a witch’s face — all made visible by light from a single brilliant star.