Sunday, May 19, 2013
By BERNIE REIM
We are now halfway through summer and the days are getting shorter by about three minutes per day. Along with the annual Perseid meteor shower, we also will have a daytime occultation of Venus, and a close conjunction of Mars and Saturn that will turn into another quadruple conjunction similar to one we had last month.
Sky Guide: This chart represents the sky as it appears over Maine during August. The stars are shown as they will appear at 10:30 p.m. early in the month, at 9:30 p.m. at midmonth and at 8:30 p.m. at month’s end. Saturn and Mars are shown in their midmonth positions. To use the map, hold it so that the direction you are facing is at the bottom.
Sky Chart prepared by George Ayers
The Perseid meteor shower will be better than last year because the moon will be three days past last quarter and won't rise until 1 a.m. on the 12th. Caused by Comet Swift-Tuttle, all the Perseids will appear to originate from one point in the sky in the constellation of Perseus the Hero.
This constellation is easy to find in the northeastern sky. You just need to follow the Milky Way from the Summer Triangle which is overhead, down past Cepheus the King and Cassiopeia the Queen, also known as the summer W. The next constellation along the Milky Way below the summer W is Perseus the Hero. It will rise around 9 p.m. by the middle of August.
The mythological story surrounding Perseus is one of the more famous and interesting. Perseus is the son of Zeus and a mortal named Danae. That made Perseus a demigod but not immortal. He slayed a gorgon named Medusa, who could turn you into stone if you only looked her in the eye.
Perseus also performed many other heroic deeds like saving the princess Andromeda, who was chained to a rock to be sacrificed to a sea monster. Perseus is now holding the head of Medusa in one hand and his jeweled sword in the other. The double cluster represents the jeweled handle of his great sword. The bright variable star named Algol, which means the Demon Star, marks the blinking eye of the slain Medusa.
You can expect nearly 60 meteors per hour this year from a dark sky site far from any lights because the moon won't interfere as much. The brilliant streaks of light you will see if it is clear are caused by something as tiny as a grain of sand and much less dense. The reason they appear so bright is they are smashing into our upper atmosphere at nearly 40 miles per second, or about twice as fast as the earth is constantly speeding through space. Most of them will burn up around 70 miles straight above us and will last for much less than one second. If the piece of comet dust is a little larger, similar to a small pebble, it would cause a fireball that could last for a full second but wouldn't hit the earth. If it did, it would be called a meteorite, and they are quite valuable. Before it burns up in our atmosphere, it is called a meteoroid.
The only annual meteor shower that is usually better than the Perseids are the Geminids on Dec. 13. But it is much colder by then and people are generally not out camping then or on vacation, so that they can leisurely enjoy one of nature's great shows. By far the best meteor shower I ever saw was the Leonids on Nov. 18, 2001. The Earth was passing through a denser part of the debris trail of Comet Temple-Tuttle that morning. The comet had also just swung by the sun again two years before on its 33-year orbit, which created more debris in its trail. I saw nearly 3,000 meteors that morning for nearly three hours straight. There wasn't a single lull for over eight seconds and I saw as many as seven meteors in one second, all emanating from a point in Leo the Lion called the radiant. That was the first time I got a sense of the earth's constant motion around the sun. We even saw about 15 brilliant bolides that lit up the earth and sky, and whose trails lingered for many minutes.
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