Bellatrix's Vital Stats:
|Gamma Orionis, HIP 25336, HD 35468, HR 1790
|Distance from Earth
|8 solar masses
|6 solar radii
|05h 25m 07s
|+06° 20' 58”
The Orion constellation is something of a gold mine, and we’ve dug into a few of these treasures in the past, including Rigel, Betelgeuse, and Alnilam. Now, we turn our attention to another shiny gem: the brilliant blue star Bellatrix on Orion’s other shoulder
If you’re unfamiliar with this star, don’t feel bad. If Bellatrix were located in just about any other constellation, it would probably be the “star of the show,” but as it stands, Bellatrix takes a backseat to brighter Rigel and Betelgeuse. It’s further overlooked because of the three-star belt and the Orion Nebula and Horsehead nebulae. However, at 2nd magnitude, Bellatrix is truly a brilliant star.
At first glance Bellatrix appears white, but a little time watching will reveal its blue color, especially in contrast to nearby red Betelgeuse. And when it comes to stars, blue means hot. The star’s surface is heated to a roaring 21,750 kelvin (40,000°F) — a difficult quantity to comprehend even though there are plenty of stars even hotter. By comparison, the Sun’s surface is about 5800K, giving it a white/yellow color. If Earth were orbiting Bellatrix, lighting conditions would be unusually blue.
Bellatrix’s spectral type of B2V is also interesting. While the star has some spectral signatures of a giant, it’s not giant yet — it’s simply a main sequence star that’s hotter and larger than the Sun, similar to Sirius. Bellatrix still has millions of years left before it enters the giant phase.
Bellatrix is something of a minor variable star, meaning that its brightness rises and falls slightly over time. But the fluctuation is both small and seemingly random, so observing the effect with amateur equipment is tricky if not downright impossible.
Eventually, Bellatrix should expand into a giant star, but its ultimate fate is unknown. Bellatrix has a mass of somewhere around 8 to 9 solar masses, but that number represents the knife-edge of a star’s future. Stars with a mass higher than this eventually form a brilliant supernova, while smaller ones quietly settle down into stellar retirement as a white dwarf. We’re not sure which path Bellatrix will take because other factors — such as how much mass it will lose toward the end of its life — are hard to predict.
Origin / Mythology
Students of astronomy know well that Orion is the great hunter of classical Greek myth. Bellatrix marks one of Orion’s shoulders, although whether it’s his left shoulder or right depends on if you imagine him facing towards or facing away (artistic representations have shown him in both positions over the centuries). Outside the Mediterranean, there is no shortage of cultures who claimed the stick figure in the sky as a great hunter, warrior, giant, and some other larger-than-life hero in their cultural lore. So it’s a curious journey to dig into the etymology of the name Bellatrix, Latin for “female warrior.”
A word meaning warrior is certainly a good fit for a star in a constellation globally associated with heroic deeds; indeed, the star’s Arabic name means conqueror. What’s not clear is why the feminine Latin form is used over the masculine form, which would be Bellator. The answer might be that the name Bellatrix has its origins in another part of the sky entirely, separate from Orion.
The name Bellatrix was already floating around in the 800s AD, attached to the star we now know as Capella (or alpha Aurigae). Around the late 15th century, star catalogers seized on the idea of transferring the name to Orion (perhaps because a warrior’s name would be more suitable for a star belonging to the Hunter.). So the name was relocated from alpha Aurigae to gamma Orionis. Orion’s shoulder was thereafter the woman warrior. Because of this, Bellatrix is sometimes called the Amazon Star, in reference to the mythical Greek characters.
Interestingly, a different Amazon — this time, the South American river — also has a connection to the star we call Bellatrix. Rainforest societies there depicted the star as a canoe piloted by a boy, with nearby Betelgeuse taking the part of an elderly man.
How to See Bellatrix
Orion is spectacular to behold and easy to find in the winter. While the precise direction you look depends on the month and the time of night, it’s always going to be in a roughly southern direction when viewed from the Northern Hemisphere. Orion isn’t a zodiac constellation like its neighbors Gemini and Taurus, but instead slides along the sky just beneath the ecliptic. Because of this, the Moon visits Orion once a month, just above his head. Orion is easy to spot for its belt of three bright stars in a line.
As for Bellatrix itself, the bright star marks the upper right shoulder of Orion when looking up from the ground. Don’t confuse it with Orion’s head, which is made up of a trio of much fainter 3rd- and 4th-magnitude stars. Bellatrix is often accompanied by a fierce twinkling similar to bright Sirius or Capella, especially when the constellation is low on the sky early on December or January evenings. Try it tonight — it’s a star you should have no trouble finding.
Daniel Johnson is a Wisconsin-based freelance writer and professional photographer and the co-author of over a dozen books. He’s a longtime amateur astronomer and fortunate enough to live in a rural region with excellent seeing conditions. You can view some of Dan’s photography (he does a lot of animals!) at www.foxhillphoto.com