Orion the Hunter is now well above the eastern horizon after evening twilight. Only the Big Dipper is a more recognizable stellar picture in the sky.
You can see how the ancients imagined it as a giant hunter. Its hourglass shape in the eastern skies, to the Greeks and Romans, outlined the to
rso of Orion.
The constellation is best noted by three bright stars in a row that make up his belt — Alnitak, Alnilam, and Mintaka. Below, and to the right of the belt, of is the famous Great Orion Nebula, visible even to the naked eye.
It’s a colossal cloud of hydrogen gas more than 1,500 light-years away, where hundreds and hundreds of young stars have, and will be, born. In coming weeks, I’ll feature the Orion Nebula in more detail.
This week I’ll tell you about Orion’s brightest stars, Rigel and Betelgeuse, anchored at opposite corners of the hunter. They are the fourth and fifth brightest stars in the local sky. Nowhere else will you see two stars this bright so seemingly close to each other.
Rigel is a super blue giant star, and Betelgeuse is a super-duper red giant star.Even with the naked eye you can see their hues, especially with Betelgeuse.
Rigel is the brightest star in Orion, slightly outshining Betelgeuse, even though according to classic star charts, Betelgeuse is considered the alpha or brightest star in the constellation. Really there isn’t much difference in their brightness.
Rigel is somewhere between 700 and 800 light-years away from earth. (A light-year, the distance light travels in one year, equals almost six trillion miles.)
The sun, our closest star, is less than a hundred million miles away by comparison. Despite being trillions and trillions of miles away, Rigel is so bright in our winter sky because it’s 60 million miles in diameter, making it 100 times the diameter of our sun, and 17 times the mass of our comparatively diminutive home star.
Most astronomers believe Rigel kicks out more than 80,000 times more light than our sun, making it the most luminous star in our part of the Milky Way Galaxy. Its outer layer has an estimated temperature just under 20,000 degrees, making it almost twice as hot as our sun.
Rigel is one big shiner, but there’s a price to be paid for all that stellar prowess. Heavier stars like Rigel don’t live nearly as long as smaller stars like our sun. They’re gas guzzlers, going through the hydrogen fuel in their cores at highly prodigious rates.
It’s hard to estimate the exact age of a particular star, since there are so many factors.
Its mass is the main contributor to a star’s life span, and the best indications are that Rigel’s total light time is less than one billion years. By comparison, our own sun sips its nuclear fuel and is expected to have a total life expectancy of around 12 billion years.
That being the case, Rigel hasn’t even been around for all that long. When dinosaurs roamed around our world, Rigel was not yet in our starry sky, and it will be out of the heavens before our sun calls it a lifetime.
At the other corner of Orion is surely the biggest single thing you’ve ever seen, Betelgeuse. It’s over 20 times the mass and 1,100 times the diameter or our sun, giving Betelgeuse an estimated girth of about one billion miles across. It’s so large, that if you put it in the place of our sun, the planets Mercury, Venus, Earth, Mars, and even Jupiter would be inside Betelgeuse.
Its diameter and reddish hue means it’s already near the end of its very short life. Most astronomers estimate Betelgeuse isn’t much more than a few million years old, and it’s already expended its hydrogen and helium fuel to the point where it’s puffed out in the red giant phase of its brief life.
No one really knows, but in maybe less than 10,000 years, a thousand years, or even next year it could blow up in a tremendous supernova, making it brighter than the full moon in our night skies for several weeks. It’s a good thing that Betelgeuse is more than 400 light-years away from Earth, because if it was much closer, it could make for a really bad day here on Earth.
It’s believed by many astronomers that if Betelgeuse were within a hundred light-years of Earth, the radiation from the nova could change or eliminate life as we know it on our planet. Keep your distance Betelgeuse.
Mike Lynch is an amateur astronomer and professional broadcast meteorologist for WCCO Radio in Minneapolis and is author of the book, “Washington Starwatch,” available at bookstores. Check his website www.lynchandthestars.com.
The Everett Astronomical Society: www.everettastro.org.
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