Rigel: The Blue Supergiant

Rigel is one of the most luminous stars visible to the naked eye, a blue-white supergiant that anchors the lower-right corner of Orion (as seen from northern latitudes). Despite being roughly 860 light-years away, Rigel shines at magnitude 0.13, making it the seventh brightest star in the sky. Its extraordinary energy output makes it a beacon of stellar power. Locate it with StarGlobe.

How to Find Rigel

Rigel marks the hunter's left foot in Orion, positioned diagonally opposite from reddish Betelgeuse. It is the brighter of the two in most observations, despite carrying the Beta designation. Its blue-white color contrasts dramatically with Betelgeuse's orange-red, and this color pairing is one of the most striking in the night sky.

From the Northern Hemisphere, Rigel is the lower-right star of Orion's rectangle. The three belt stars sit between Rigel and Betelgeuse. Rigel also serves as one corner of the Winter Hexagon, a large asterism connecting six bright stars: Sirius, Procyon, the Gemini twins, Capella, Aldebaran, and Rigel.

Physical Characteristics

Rigel is a blue supergiant of spectral type B8Ia, with a surface temperature of about 12,100 Kelvin. Its luminosity is estimated at 120,000 times that of the Sun, making it one of the most intrinsically bright stars in our region of the galaxy. If Rigel were placed at the distance of Sirius (8.6 light-years), it would appear nearly as bright as the full Moon and cast visible shadows.

The star has about 21 times the Sun's mass and a diameter roughly 79 times the Sun's. Despite being smaller than Betelgeuse, Rigel radiates far more energy because of its much hotter surface. It is a young star, likely only 8 to 10 million years old, having formed from the same molecular cloud complex that produced many of the other bright stars in Orion.

Rigel shows slight brightness variations of about 0.03 to 0.3 magnitudes, classifying it as a low-amplitude variable star. The variability is caused by pulsations in its outer layers, similar to but less dramatic than those seen in Betelgeuse.

The Rigel System

Rigel has at least one known companion star, Rigel B, a bluish star of magnitude 6.7 located about 9 arcseconds from the primary. Rigel B is itself a spectroscopic binary, making the system at least triple. Observing Rigel B is challenging due to the overwhelming glare of the primary, but it is achievable with a 6-inch or larger telescope under steady seeing conditions. The companion has been used as a test of telescope optics and observer skill.

Rigel in Context: The Orion OB1 Association

Rigel is a member of the Orion OB1 association, a large group of hot, young stars that formed from the same giant molecular cloud. This association includes many of the bright stars in and around Orion, including the belt stars. The association is divided into several subgroups of different ages, with Rigel belonging to one of the older subgroups despite its youth by stellar standards.

Like Betelgeuse, Rigel will eventually end its life in a supernova explosion, though as a blue supergiant it is at a different evolutionary stage. Some astronomers believe Rigel may expand into a red supergiant phase before exploding, while others suggest it could detonate directly from its current blue supergiant state.

Cultural Heritage

The name Rigel comes from the Arabic "rijl al-jawza," meaning "the foot of the central one." The star has been important in many cultures. Ancient Egyptians associated it with Sah, the celestial embodiment of Osiris. In Maori tradition, Rigel is known as Puanga, a star whose rising marks the beginning of the new year and the Matariki celebration period.

In modern science fiction, Rigel and its hypothetical planetary system have been frequently referenced, appearing in Star Trek and other franchises as the home of fictional civilizations.

Best Time to Observe

Rigel follows the same observing season as Orion, best seen from December through March. The star culminates during January evenings. Its blue-white color is easiest to appreciate when it is high in the sky, minimizing atmospheric reddening near the horizon.

Neighboring Stars

Betelgeuse sits diagonally opposite in Orion. Sirius lies to the southeast, and Aldebaran in Taurus is to the northwest. The three belt stars of Orion connect Rigel and Betelgeuse. Below Rigel, the constellation Lepus (the Hare) contains several interesting targets. Explore Rigel's neighborhood with StarGlobe.

Quick Facts

Rigel has an apparent magnitude of 0.13, a distance of approximately 860 light-years, and a luminosity about 120,000 times that of the Sun. Its mass is roughly 21 solar masses, and its surface temperature is about 12,100 Kelvin. Its right ascension is 5h 14m, and its declination is -8 degrees 12 minutes.