Orion, the great celestial warrior, is the grandest and most brilliant of all the constellations. It’s visible from every inhabited part of the Earth and shines down upon us through the frosty air all winter long. Its most recognizable feature are three bright stars which decorate Orion’s belt—a diagonal line in the middle of a luminous rectangle. These stars point northward to the clusters of the Hyades and Pleiades of Taurus and southward to the brightest star in the sky, Sirius.
Within Orion we find two immense stars, Rigel and Betelgeuse, apparently at two entirely different periods in a star’s existence. In Rigel (the “Left Leg of the Giant”), we find a star apparently reaching the prime of its life. It’s a true supergiant: a blazing white-hot star of intense brilliance and dazzling beauty. Located 900 light years away, its computed luminosity is roughly 36,000 times the brightness of our Sun.
Betelgeuse (“The Armpit of the Giant”) in contrast, shines with a cool, dull ruddy hue and is located 500 light years away. It is an irregular pulsating supergiant star, nearing the end of its life and as such it expands and contracts spasmodically. Incredibly, its diameter can vary between 550 to 920 times the diameter of our Sun.
Put another way, if our Sun were reduced to the size of a baseball, Betelgeuse at its maximum size would be a globe measuring 176 feet across!
As is also the case with the mighty Hercules, the figure of Orion has been associated in virtually all ancient cultures with great national heroes, warriors, or demigods. Yet, in contrast to Hercules, who was credited with a detailed series of exploits, Orion seems to us a vague and shadowy figure. The ancient mythological stories of Orion are so many and so confused that it is almost impossible to choose among all of them. Even the origin of the name Orion is obscure, though some scholars have suggested a connection with the Greek “Arion,” meaning simply warrior. All, however, agree that he was the mightiest hunter in the world and he is always pictured in the stars with his club upraised in his right hand. Hanging from his upraised left hand is the skin of a great lion he has killed and which he is brandishing in the face of Taurus, the Bull, who, in the stars, is charging down upon him.
The Great Orion Nebula
Also within the boundaries of Orion is undoubtedly one of the most wonderfully beautiful objects in the sky: the Great Orion Nebula. It appears to surround the middle star of the three in line that marks the hunter’s sword. It’s invisible to the unaided eye, though the star itself appears a bit fuzzy. It is resolved in good binoculars and small telescopes as a bright gray-green mist enveloping the star. In larger telescopes, it appears as a great glowing irregular cloud. A sort of auroral glow is induced in this nebula by fluorescence from the strong ultraviolet radiation of four hot stars entangled within it. Edward Emerson Barnard (1857-1923), for many years an astronomer at Yerkes Observatory, once remarked that it reminded him of a great ghostly bat and that he always experienced a feeling of surprise when he saw it. Known also as Messier 42, the Orion Nebula is a vast cloud of extremely tenuous glowing gas and dust, approximately 1,600 light years away and about 30 light years across (or more than 20,000 times the diameter of the entire Solar System). Astrophysicists now believe that this nebulous stuff is a stellar incubator; the primeval chaos from which star formation is presently underway.
Joe Rao is an esteemed astronomer who writes for Space.com, Sky & Telescope, and Natural History Magazine. Mr. Rao is a regular contributor to the Farmers' Almanac and serves as an associate lecturer for the Hayden Planetarium in New York City.