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Mike Lynch’s Skywatch: Galactic happenings and clear autumn skies



Mike Lynch’s Skywatch: Galactic happenings and clear autumn skies

Happy astronomical autumn! Summer switched over to autumn last Wednesday afternoon at 2:21, the moment of Autumnal Equinox. The sun’s daily arc across the sky from east to west will continue to get shorter, shrinking daylight until the first day of winter in December. Selfishly, shrinking daylight is fine by me because nights are longer for stargazing.

A great way to kick off the autumn stargazing season is to make a date to get out under the dark skies of the countryside, if you’re not already living there. Now that last week’s harvest moon is leaving the early evening sky, this will be a great week to head out. The clear autumn skies are more transparent because of much less moisture in the air.

I guarantee that this will be a treat that you’ll remember for a long time, no matter if you’re by yourself or with family or friends. Bring the blankets, binoculars, star charts, snacks and beverages, and be prepared to sleep in the next morning. Even better, turn this into an early autumn overnight campout.

Just for kicks, try to estimate how many stars you can see without the help of binoculars or a telescope. Traditional astronomy textbooks say that you can see about 3,000 stars with the naked eye. Don’t even try to count the stars, or you’ll fall asleep and the show will be over. In the dark countryside, you can’t help but notice the ghostly band of milky light that bisects the sky from roughly north to south. It’s a cosmic artist’s stroke across the heavens. That’s the Milky Way band. Every star you see, including the sun, is a member of our home galaxy, the Milky Way. The Milky Way band comprises the combined light of billions and billions of extremely distant stars that make up the plane of our galaxy. We’re looking edgewise into that plane. It’s the thickest part of the Milky Way.

No one knows for sure, but there may be well over 300 billion stars in our home galaxy, forming a nearly circular disk that’s broken up into spiral arms. There’s a massive globe of stars in the center. The Milky Way is a little more than 100,000 light-years in diameter and, on average, is 10,000 light-years thick. By the way, just one light-year equals nearly 6 trillion miles. Our sun is about 30,000 light-years from the galaxy’s center, located in one of the spiral arms.

All of the stars we see obediently orbit around the center of the Milky Way. Our sun takes over 200 million years to make one circuit. In case you’re wondering, the center of the Milky Way lies in the direction of the constellation Sagittarius the Archer in the low southwest sky. Sagittarius’s nickname is “the Teapot” because that’s what it really resembles. The Milky Way band is not all that much brighter around the teapot because there is a lot of dark interstellar gas and dust that blocks the globe of stars at our galaxy’s center. If we could see the Milky Way’s central region unobstructed, that area of the sky would possibly be as bright as a full moon.

Lie back on the ground or a reclining lawn chair and roll your eyes from one end of the Milky Way band to the other. A decent pair of binoculars will greatly enhance the celestial treasures you come across, like bright patches, dark rifts, and star clusters. You might even see a few human-made satellites roaming across the heavens.

While you’re enjoying our galaxy, keep in mind that the Milky Way is only one of millions of other galaxies out there. Astronomers have spotted billions and billions of galaxies more than 13 billion light-years away. It’s a big sky out there for you to enjoy. Don’t miss it!

Mike Lynch is an amateur astronomer and retired broadcast meteorologist for WCCO Radio in Minneapolis/St. Paul. He is the author of “Stars: a Month by Month Tour of the Constellations,” published by Adventure Publications and available at bookstores and Mike is available for private star parties. You can contact him at [email protected]

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