Meet Betelgeuse, the Red Giant of Orion


Official name (IAU-approved) Betelgeuse
Other Designations Alpha Orionis
Apparent Magnitude 0.42
Distance from Earth ≈ 600 light-years
Type Red supergiant (M1-M2 Ia-Ibe)
Color Red
Mass ≈ 15 M
Radius ≈ 1,000 R
Constellation Orion
Right Ascension 5h 55m 10.30s
Declination +07° 24' 25.43''
Multiple system? No
Variable star? Yes, semiregular variable
Exoplanets status None known
Probable fate Supernova

Physical Characteristics

Betelgeuse is a colossal object — and a very bright one at that. As a red supergiant nearing the final phases of its life cycle, Betelgeuse has an estimated diameter around a thousand times that of the Sun, with an estimated absolute luminosity of 100,000 times the Sun. We’re talking about an object larger than the entire orbit of Jupiter — an amazing fact to recall the next time you’re out observing this star.

Its immense size makes its distance uncertain, though, which makes calculations of other properties (such as its mass) uncertain too. Its distance is measured by its parallax, which the Hipparcos satellite measured as 6.55 milliarcseconds (which would give a distance of 500 light-years). But the star itself spans 45 milliarcseconds on the sky — as you can imagine, that complicates measurements of its motions on the sky. Radio interferometry has resulted in more precise distance measurements around 640 light-years in 2008 (though combined measurements published in 2017 give an even farther distance of 720 light-years). Ultimately, the Gaia satellite’s exquisite parallax measurements may help decide the distance debate.

Regardless of its distance, observations do make one thing clear: Betelgeuse is destined to go supernova relatively soon, astronomically speaking. Depending on whom you ask, “soon” could mean it has another 100,000 years, or perhaps up to a million years, to live.

Stars are in constant motion. It’s only because of their immense distance that we fail to see their motions within the timescale of our lifetimes. Betelgeuse is an excellent example of this — in just 100,000 years, it will leave its home in the Orion constellation.

The following video animates the current motions of stars in Orion, projecting them 450,000 years in the future. Betelgeuse moves out of the field of view in just 100,000 years.

Betelgeuse is a star in a hurry — travelling through space at about 67,000 mph (30 km/s) relative to the surrounding interstellar medium. For comparison, the Apollo Command Modules returning astronauts from the Moon reached speeds of around 25,000 miles per hour, and the New Horizons probe exploring the Kuiper Belt travels around 36,000 miles per hour.

Betelgeuse is moving so fast that the interaction between its stellar wind and the surrounding interstellar medium creates an immense bow shock 3 to 4 light-years wide. (The bow shock is visible at infrared wavelengths, so don’t expect to see it through your scope!)

Betelgeuse's bow shock

The European Space Agency's Herschel satellite captured this infrared view of Betelgeuse. The supergiant has ejected some of its outer layers in a wind, which has been shaped into a bow shock as the star hurtles through space.
ESA / Herschel / PACS / L. Decin et al.

Origin / Mythology

In Arabic, the name Betelgeuse can be translated as “shoulder of the giant.” Many cultures throughout history identified Orion as a hunter or giant. To the ancient Egyptians, the constellation was Osiris, a god and primeval king in the culture’s mythology. In some myths originating in the Americas, Betelgeuse represented a wound on Orion, perhaps because of the star’s red color. Betelgeuse also features in Aboriginal Australian mythology, as passed down through oral tradition.

How to See Betelgeuse

Finding the brilliant red giant is an easy task, thanks to its prime location in a prominent constellation. In the Northern Hemisphere, Orion begins to rise early in the evenings in December, and continues to dominate the southern winter sky until about April, when it begins to fade into the sunset. Betelgeuse is in the upper left-hand corner of Orion when viewed from an “upright” perspective.

Betelgeuse vs. Rigel

The author photographed this view of Orion, showing the color difference between the red supergiant Betelgeuse and the blue star Rigel.
Daniel Johnson

Once you’re aware of the red giant’s color and go looking for it, you should be able to clearly perceive its rusty hue in comparison to other nearby stars. Try comparing red Betelgeuse to the blue star Rigel (Orion’s left foot). And if you’d really like a clear view of the colors, try taking a 15- or 20-second exposure of Orion with tripod-mounted camera. Nothing brings out the colors of the night sky like a photograph! Have fun.

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