Starwatch: The big guy of the night sky is back
It’s back! My favorite constellation, Orion the Hunter, has once again resumed his full rein in the early evening southeastern sky along with his entourage of bright constellations. I love to refer to this collection as "Orion and his gang." In fact, out of the 20 brightest stars seen in Minnesota and Western Wisconsin skies, 11 of them are residents of Orion’s gang!
Without a doubt, Orion is the marquee constellation of winter. Even in heavily lit urban skies, Orion’s stars pierce through. To me at least it resembles both a crooked bowtie or an hourglass. In Greek and Roman mythology its stars outline the torso of a giant and heavily bulked hermit hunter. Orion is portrayed in the night sky holding a shield in one hand and raising a sword with the other. It’s quite a tale as to how this hermit hunter wound up among the stars that I’ll share with you next week in Starwatch.
The constellation is a celestial treasure chest. There are so many fantastic telescope targets, even ones for smaller scopes. This week I want to tell you about the best ones. Honestly, if I tried to cover all of Orion’s treasures I would hog up this entire section of the paper!
By the way with the colder weather this time of year I like to remind telescope users that it’s essential to set up your telescope outside along with all the eyepieces you’ll be using for at least a half-hour before you begin your viewing. The lenses and or mirrors need to acclimate to the colder outside temperature. Otherwise, the views through your scope might be a little fuzzy.
Orion’s best visual calling card is his belt made up three bright stars neatly lined up like stellar soldiers. They are Alnitak, Alnilam, and Mintak. Nowhere else in the sky from any spot on Earth will you see three stars as bright as they are so tightly lined up. One could easily conclude they’re in the same celestial neighborhood but in reality, they’re a long way from each other! They’re hundreds of light-years apart. Even though we see constellations as two-dimensional "pictures," we’re actually looking into three-dimensional space. Alnitak is 800 light-years away, and by the way, just one light-year is nearly six trillion miles. Alnilam is 1,300 light-years distant, and Mintaka shines away at us from 900 light-years. It’s just by sheer coincidence (or not?) that these three stars line up as they do from our vantage on Earth.
There’s another coincidental line up of three dimmer stars to the lower right of Orion’s belt that depicts his sword. Just with your eyes though, you can see that the middle star in the sword is a little fuzzy. That’s because it’s not a single star but rather a tremendously vast cosmic cloud of hydrogen called a nebula. Even as you read this column, new stars are forming within it. The Great Orion Nebula, as it’s known, is over 1400 light-years away and over 30 light-years across. To get an idea of how big that is, you could line up 20,000 of our solar systems, end to end across it!
This colossal birthing ground of stars is visible mainly because of four very energetic stars born within it that light up the nebula like a florescent light. Because of that the Orion Nebula is known by astronomers as an emission nebula. Even with a small to moderate telescope you should be able to resolve those four young stars arranged in the shape of a tiny baseball diamond. Formally they’re known as the Trapezium stars and all four of them are probably less than a million years old, which believe it or not classifies them as stellar infants! In truth, the lit-up Orion Nebula is only a small portion of a much larger hydrogen cloud giving birth to many, many more future stars.
On the upper left-hand corner of Orion is, without a doubt the biggest single thing you’ve ever seen without a telescope. It’s the star Betelgeuse, which is an Arabic name that arguably translates to "armpit of the great one." That’s right. It’s Orion’s armpit. Astronomers categorize Betelgeuse as a super red giant star more than 1,000 times larger than our sun, which would give it a diameter of nearly a billion miles! If you were to put Betelgeuse in the place of our sun in our solar system, its girth would stretch out to near the orbit of Jupiter. The behemoth star would engulf Mercury, Venus, Earth, and Mars.
Betelgeuse is considerably younger than our sun, estimated by astronomers to be about 10 million years old. Our sun is believed to have been around for about 5 billion years and should stay more or less in its present state for another 5 billion years. Supergiant stars like Betelgeuse die young since they squander their resources at a very rapid rate. They’re considered the gas guzzlers of the stellar world.
Betelgeuse may meet its demise within a million years, or possibly even within a few thousand years. In the last several years, Betelgeuse has been dimming a bit which some astronomers take as a sign that the explosion is coming soon. Whenever it happens, it won’t go out quietly. Stars the size of Betelgeuse literally blow themselves to bits in what’s called a supernova explosion. We’ll undoubtedly see this from Earth. When Betelgeuse blows up, it’ll turn nearly as bright as a full moon in our sky and could stay that bright for at least a couple of weeks. It might even be visible in the daytime! The good news is that Betelgeuse’s blast won’t harm the Earth. It’s too far away at a distance of better than 500 light-years. If our world were within 50 light-years of Betelgeuse, It would be a terrible day for us!
There are many more celestial treasures in Orion. Just put the name Orion in any search engine and read away, or better yet download a planetarium program. My favorite is "Stellarium." Not only is it terrific software, but it’s also free! Another great resource is the Sky Guide App that you load in your smartphone for less than five dollars. Whatever you do, with or without a telescope, try to view Orion from truly dark skies in the countryside. You’ll thank me for sending you out there!