Starwatch: It's a perfect time to catch the Perseids
The days of summer are starting to wane, the back-to-school ads are running full bore, and the meaningless NFL preseason games have begun. One good thing you can rely on this time of year is the annual Perseid meteor shower, one of the best of the year. There are about a dozen meteor showers a year, but the Perseids are special, because it's not only prolific, but you watch them without freezing your rear off!
The show has been going on in the Rochester sky since the beginning of August, and it's peaking this weekend as well as Monday morning. The best time to see the Perseids is after midnight, especially from 2 a.m. to 5 a.m.
The Perseids are extra-special this year because there's no moonlight interference in the early morning hours, leaving us with dark skies. If you can get out into the countryside for the really dark skies, all the better. You may see 50 to 80 meteors or more "shooting stars" an hour. Maybe more than one every minute! Even in more lit urban areas, you'll see at least 5 to 10 an hour with a little perseverance.
The Perseids are called the Perseids because all of the meteors seem to emanate from the general direction of the constellation Perseus the Hero. Perseus is said to be the radiant of this meteor shower.
Perseus the Hero rises high in the northeastern sky in the early morning hours. Whatever you do, though, don't restrict your meteor search to just that part of the sky. If you do, you'll miss a lot of them. My advice for watching the Perseids or any other meteor shower is to lie back on the ground or a reclining lawn chair and roll your eyes all around the sky.
Watching a meteor shower is a great way to spend a summer night, and watching with family and friends is even more fun. The Perseids are famous for the number of meteors you see, but most of them are faint and rip across the sky rapidly, so the more eyes watching the big sky the better.
Meteors are often called shooting stars. They do look like stars, but they're actually just grains of dust and pebbles. The biggest ones may approach the size of small walnuts. This is all debris left behind by comets that have passed by the Earth and our sun.
Comets are basically dirty snow and ice balls that partially melt when they get close to the sun. Debris from these partially melted comets is left in their wake, and gravity between the particles keeps the debris trail intact. Meteors from meteor showers are best seen after midnight because then we are on the side of the Earth heading into the debris trail, as you can see in the diagram.
The debris trail that causes the Perseids is from Comet Swift-Tuttle, which comes by this part of our solar system about every 130 years. It last passed in 1992.
Because of that recent visit, the Perseid meteor shower was even more prolific in much of the 1990s, but even now it's still a great show. There were some who thought that Swift-Tuttle could possibly collide with the Earth in 2126, but that's been played down by a lot of astronomers. Stay tuned though!
In the meantime, tiny pieces of Comet Swift Tuttle will slam into our atmosphere at speeds over 40 miles per second, easily incinerating them before they can get anywhere near you. Most bits of this debris burn up around 40 miles high.
There's no way you can see these bits burn up at that height. How could you? So where does the light come from? The answer is the process of ionization. These debris particles are zipping through our atmosphere so fast that the column of air they're going though is being destabilized. Zillions of electrons from atoms that make up Earth's atmosphere get temporally bounced away from the nucleus of zillions and zillion of atoms.
As these electrons bounce away and then bounce back, they produce energy in the form of bright light. In fact, a lot of meteors you see leave a trail that can take a few seconds to fade. What you're seeing is the column of air that the meteor ripped through stabilizing and getting its act back together.
I strongly advise that you get your act together and catch the Perseids. It's one of Mother Nature's best shows of the year. Don't forget the bug juice!
On Monday night, the crescent moon will be parked just below the bright planet Saturn. It will be great to gaze at with just your eyes, but if you point even a small telescope at both the moon and Saturn, it will make it that much better. It may be a little fuzzy, but you should be able to make out Saturn's ring system with your scope.
Mike Lynch is an amateur astronomer and professional broadcast meteorologist for WCCO Radio in Minneapolis/St. Paul and is author of the book, "Stars, a Month by Month Tour of the Constellations" published by Adventure Publications.
The Rochester Astronomy Club welcomes new members and puts on public star parties. Their website is: http://www.rochesterskies.org
If you have any astronomical questions or want me to write about something you're seeing in the night sky, drop me a line at email@example.com.