BY MIKE LYNCH
You and I are a tiny, tiny part of something that’s beyond enormous!
Our Earth, solar system, sun and up to 400 billion other stars, along with Lord knows how many other planets going around those other stars, are all orbiting around our home Milky Way Galaxy. You can’t describe how enormous it is very easily with miles, because if you did the numbers would remind you of the U.S. national debt! One light year, the distance that a light beam would travel in a year, is just short of 6 trillion miles. That is a six followed by 12 zeros!
Our Milky Way is believed to be a spiral disk of stars with a big bulge in the middle. It spans well more than 100,000 light years in diameter, but the thickness of most of the disk is very thin by comparison, around 1,000 light years. The central bulge of our home galaxy is about 12,000 light years in diameter.
Every time you look up on a clear night, even if you’re gazing in an area mired with light pollution, every one of the stars you see is a neighbor star in our home galaxy. In fact, most of the stars you see at a glance are very close Milky Way neighbors. To get a better idea of the vastness of the Milky Way get out into the countryside where the sky is pitch dark. Take binoculars or a small telescope with you to really make the night special!
As twilight fades, you can tell right away how special the night sky can really be when you’re away from city lighting! Lie back on a blanket or lawn chair so you can really take it all in! It’s especially thrilling this time of year because you can see that big river of stars that cuts the sky nearly in half. That river is more formally known as the Milky Way band, stretching from the northeast horizon, through the overhead zenith, on to the south-southwest horizon. You are looking edgewise into the plane of our Milky Way Galaxy, 1,000 light-years thick. There are so many stars in our line of sight that it’s impossible to see most of them individually. Instead they merge into one continuous glow.
The center bulge of the Milky Way is located toward the southwestern horizon. It’s a little brighter than the rest of the band, and would be a whole lot brighter if there weren’t gargantuan clouds of gas and dust in the way. Some astronomers think that if it weren’t for all of the astronomical crud in the way, that part of the sky would be as bright as the full moon all of the time!
While you’re rolling along the Milky Way in the Pottsville sky, the bright planets Jupiter and Saturn will jump out at you on the southern end of the band. Jupiter is the brighter of the two. They just happen to be in the foreground of the river of stars this year. The largest planets in our solar system aren’t quite as bright as they were this summer, but they’re closer and closer to each other in the sky. Of course, they’re nowhere near each other physically, but are nearly in the same line of sight. As autumn continues, Jupiter and Saturn will draw even closer to each other. On Dec. 21, they’ll almost be “touching” at only a tenth of a degree apart! It will be the closest they’ve been to each other since 1623!
Nowhere near the Milky Way band is an incredibly bright red “star” launching above the horizon after 9 p.m. That’s Mars, setting up for another close encounter with the Earth next month. Stay tuned to Starwatch for more in the coming weeks.
Sadly, this is the last weekend of summer. Autumn begins Tuesday morning at 8:30 a.m., the moment of the autumnal equinox. At that time, the sun’s daily arc across the sky from east to west slips below the celestial equator, a projection in the sky of the Earth’s terrestrial equator. For the next six month, the sun’s daily arc across the sky will stay completely in the southern half of the celestial dome. It will also get lower and lower until the first day of winter on Dec. 21. As that happens, we’ll lose even more daylight hours. That suits me just fine, as the nights for stargazing become longer and the stars are out earlier in the evening. You just need a heavier coat!
Celestial happenings this week
The first quarter moon will be passing just a little below the bright planets Jupiter and Saturn this Thursday and Friday. You’ll easily see these celestial “huggings” in the early evening low southern sky.
Mike Lynch, an amateur astronomer and professional broadcast meteorologist, can be reached at firstname.lastname@example.org.