Eye Astronomy #6: The Mighty Hunter
by Dale E. Lehman
One of the most brilliant regions of the night sky, at least for northern hemisphere observers, climbs up the eastern sky in January. Sprinkled with no less than seven stars of first magnitude or brighter, it’s home to the brightest star in Earth’s sky and dominated by the most impressive constellation of them all: Orion, the hunter.
Let’s count those bright stars. First and foremost is Sirius, the “Dog Star,” so called because it marks the eye of Canis Major, the larger of Orion’s two hunting dogs. Sirius blazes in the sky at magnitude -1.45, far brighter than any other star, outshone only by Venus, Jupiter, and sometimes Mars. Jupiter and Mars are in fact nearby right now, shining at magnitudes -2.69 and -1.52 respectively. Jupiter is easily spotted because it’s just so bright, Mars because of its orange hue. You can locate them during January around 9:00 PM using this chart:
Why is Sirus so bright? Two reasons. First, it is, in fact, a very bright star, shining with a luminosity 25 times that of our own sun. Second, it’s very close, only 8.7 light years away. It’s the brightest and most massive star within 20 light years of Earth.
The other six bright stars in this part of the sky, from brightest down, are Capella in Auriga (magnitude 0.05), Rigel in Orion (0.15), Procyon in Canis Minor (0.40), Betelgeuse in Orion (0.45), Aldeberan in Taurus (0.85), and Pollux in Gemini (1.15). Castor, Pollux’s twin, is also a
pretty bright star of magnitude 1.90. And many other reasonably bright stars scattered among them.
Let’s focus on Orion for a moment. Orion may be the most-recognized constellation of all. Nearly anyone who looks at the stars can recognize the Big Dipper, but that’s an asterism—a group of stars forming a picture. The Big Dipper is just the brightest part of the constellation Ursa Major (the great bear), whereas Orion is a constellation all his own. And he is a stunning fellow.
A rectangle of four bright stars, Rigel and Betelgeuse among them, outline the hunter’s body. A nearly straight line of three more bright stars form his famous belt, while three more stars descend from the belt, comprising his sword. The belt stars are all approximately magnitude 2. And the sword stars? That’s complicated.
If you train binoculars or a telescope on those stars, you’ll see something astonishing. Each of them is a group of stars, the combined light of which makes them bright enough to notice. And that center star is more than just a star. It’s a big patch of bright haze: the Orion Nebula.
The Orion Nebula is fascinating. With a mass 2,000 times that of our sun and a width of 24 light years, it’s a “stellar nursery,” a region where stars are actively being born as gas and dust contracts under the force of gravity. It lies about 1,344 light years away, is the brightest nebula in the sky, and the closest region of massive star formation to our Earth. At its core, a group of four hot, young stars known as the Trapezium blaze forth, blowing out a hole in the nebula. Overall, the nebula contains some 700 stars in various stages of formation. If you come to one of our open houses while Orion is in the sky, ask to see this wonder through one of our telescopes. It’s an experience you won’t want to miss!
Orion and his companions offer a great many awe-inspiring sights, both to the naked eye and to those equipped with binoculars and telescopes. Yes, you have to bundle up, but one of the greatest pleasures astronomy has to offer is merely gazing at this region of the sky and pondering what you’re seeing.
Because the Orion Nebula is only one of many awe-inspiring objects up there. Here’s one more to think about: Betelgeuse is a red giant star in the last stages of its life. Sometime in the next 10,000 to 100,000 years, it will blow off most of its mass in a supernova explosion. In fact, it might already have happened. Betelgeuse lies 498 light years away. Maybe it’s already exploded, and we’re just waiting for the light from the event to reach us. Whenever that happens, it will likely be the most spectacular supernova ever seen on Earth, possibly shining as bright as the first or last quarter moon (a “half moon”) for over three months!
Wow.
