THE SKY THIS AUGUST: EARTH IS HEADED FOR THE COSMIC DUSTBIN

You've seen Deep Impact. You've seen Armageddon. Now it is time for reality. It is with some apprehension that I report to readers that the Earth is poised to slam into the debris trail of a dying comet.

The Real Celestial Event (RCE) will occur on the night of August 11 and early morning hours of the 12th. At that time the orbital velocity of the Earth will combine with the speed of the comet debris to launch material into the Earth's atmosphere at over 60 miles per second.

At these speeds the debris will rush into our atmosphere with so much energy that the molecules and atoms that make up our atmosphere will be torn apart. So much energy will be deposited in such a short period of time that the air will heat up to thousands of degrees. As the molecules and atoms try to reassemble themselves they will give off light and the atmosphere will begin to fluoresce.

As the RCE continues, rock and metal will become vaporized and smoke and debris will follow along behind and remain suspended in the Earth's atmosphere for some time to come.

As the fiery projectiles approach the surface of the Earth, you may even be able to hear their roar in the sky. Some may even explode as their fragile bodies give way to the astronomical forces tearing at them.

Most, however, will burn up many miles high in the sky and people will shout out, "I just saw a falling star!" But, in fact, what they have seen is called a meteor. And the RCE I have just described is called a meteor shower.

The above facts are all true. But don't be alarmed. Most meteors come from debris the size of sand and gravel. It takes an object the size of your fist to actually make it to the ground. The comet in question is comet Swift-Tuttle and was the first comet to be associated with meteor showers. Comets are like the character Pigpen in the popular cartoon series, Peanuts. Pigpen, like the comets, leaves a dusty trail wherever he has been.

Infrared telescopes, in fact, can trace out the dust left behind by the comets throughout their entire orbit. Some of the comets have orbits which intersect the Earth's orbit. When the Earth sweeps into the debris trail, they burn up in the atmosphere. We see the event as a meteor shower.

The Perseids, as the August shower is called, is so named because they appear to be coming toward us from the constellation Perseus. The watching of the Perseids shower is a yearly tradition at our house. The family used to complain about getting up at midnight but after a few years they have resigned to the fact and patiently get out their blankets to lay down on the ground to watch nature's sights.

During a typical meteor shower you can expect to see a good meteor about once per minute. Some years are better than others. This year may not be the best of years as the third quarter moon rises about midnight and brightens the sky so much that only the brightest meteors will be seen. So plan your viewing time before midnight.

By the way, if you have a 35 mm camera with a "B" setting on the shutter speed you can photograph the meteors with medium speed film by simply holding the shutter open for a few minutes (use a shutter release cable). All the stars will trail in the same direction so that any streak of light on the film not in the same direction as the stars will be a meteor.

The Milky Way continues its march up the eastern sky this month and puts on a grand show around midnight. Although the summer months are frequently hazy, once we get the night to cool off and get the moisture to condense into dew the sky will clear and reveal the summer sky.

The bright star Vega is almost overhead at sunset. Because the direction of the Earth's axis of rotation slowly wobbles around a circle (once every 26,000 years) Vega will someday become our "North Star". It will then be easy to determine North as Vega is one of the brighter stars in the sky.

The constellation Sagittarius is on the southern horizon. Although it is supposed to be a half man, half horse figure shooting an arrow it always looked like a teapot to me. The Milky Way looks like steam coming out of the spout. Good thing I wasn't an early shepherd who defined the constellations for us. If you have a good clear view of the horizon in the south, the entire constellation Scorpius can be seen and you can follow its curved tail all the way around.

For readers who have a small telescope, there are several interesting objects along the Milky Way including a spherical swarm of a few hundred thousand stars called a globular cluster (M13), a planetary nebulae called the ring nebular (M57), as well as a star formation region called the Lagoon nebulae (M8).

Popular magazines can be found at your local bookstore or supermarket giving detailed descriptions of the sky and observation tips including Sky & Telescope and Astronomy magazines. A map accompanies this article showing the brighter stars. Hold it overhead and make sure the label of the direction you are facing is at the bottom of the chart.

If you have any questions or comments, please contact me at (573) 651-2172, or cobb@physics.semo.edu.

In the meantime watch out for incoming!

Dr. Michael Cobb is chairman of the physics department at Southeast Missouri State University.