ASTRONOMY CLUB NEWSLETTER

NEXT MEETING: Wednesday, August 12, 1998, at 8:00 P.M.
WHERE: AT Fairfield Elementary School, Davis.

CLUB EVENTS:
[Club member wins prize!]

THE ASTRONOMY CLUB'S "BIG ONE," THE ANNUAL PERSEID METEOR SHOWER PARTY WILL BE HELD:

What to Do There? You don't need a computer or a telescope or a beeper or your cellular phone. You needn't make a sound. Maybe you will want to just lie on your blanket, soak up some starlight, leave without saving anything to anyone--it's OK!. Or maybe this occasion would be a great opportunity to stay up all night with a friend watching for shooting stars. Or you might be puzzled by what you see and ask an anonymous question in the dark and someone will attempt to supply a correct answer. This is about the most low-key low-tech way imaginable to "learn" about the sky

What to Bring? There are some items you'll want to bring with you to observe regardless of where you decide to observe. Binoculars are optional; but warm clothes, something relaxing to sit or lie on that will protect you from the heavy dew, mosquito or gnat repellant, a flashlight in a paper bag or with a red filter (to keep lights dim) are more important. A warm non-alcoholic drink can be helpful (alcohol will cause drowsiness and reduce visual acuity) If you are joining us at Fairfield School please remember that the school's restrooms are not available.

How to watch? Try to lay or sit so that you can see as much of the unobstructed sky as possible-the direction you are facing is irrelevant. The darker the sky, the more meteors you will see. You can expect to see a bright meteor approximately every 15 minutes from our site. Certainly Fairfield School is not what astronomers consider a "dark" site such as the Blue Canyon airport off Highway 80, where the Sacramento Valley Astronomical Society hold many astronomical events.

Why Do We Need a Dark Sky? If you follow local government news in Davis you may have noticed that a Dark Sky ordinance is being debated. If you never escape the glare of the city's night lights you may not be aware of what you are missing. Perhaps an evening outside the city, even from a site as close to Davis as Fairfield School, might demonstrate one reason why Dark Sky ordinances have succeeded. At one Shower Party a guest discerned a "large column of smoke" rising over Dixon and wondered whether it was from a major fire. What he was seeing, for the first time, was our home galaxy, the Milky Way. He realized that his visible universe was suddenly much larger than he had imagined.

What is a Meteor Shower? Every year, around August 12, the Earth enters an area of its orbit around the sun that lies close to the orbit of Comet Swift-Tuttle. The debris from this comet creates the Perseid Meteor shower, the most popular and most famous of all showers. As we watch the late night sky in mid August, this debris -mostly particles the size of grains of sand--will be traveling 30 or 40 miles per second and vaporizing into incandescent streaks as they incinerate in Earth's protective blanket of air. This shower is notable for its constancy and for the rapid movements of the meteors as they streak through the sky. Approximately 45 percent of the meteors leave "trains" or smoke-like trails that persist for a few seconds.

Why Perseid? The Perseid meteor shower gets its name from the location of the radiant of the shower in the constellation Perseus. The radiant is an optical illusion, appearing to be a point in the sky from which the meteors originate. The Comet debris that enters our atmosphere is actually travelling in parallel paths around the sun, but from our perspective, it seems the meteors are "radiating" from one spot in the sky to all other areas of the sky. The phenomenon is somewhat similar to standing between a pair of railroad tracks and looking at them as they appear to converge to one point on the horizon. The tracks, like the paths of the comet dust, appear to radiate in two directions toward you, but in fact, the lines are parallel.

That meteor showers were the result of comets was surmised, though not proven, by an American, Edward Claudius Herrick in 1838, who investigated historical accounts of meteor displays and actually documented the history of the Perseid shower as a periodic event. However, this Connecticut amateur ultimately had to concede that 2 other investigators had discovered the annual nature of the Perseid shower independently (and earlier) in Brussels and Cincinnati. Herrick's evidence was more complete and compelling, however. In Herrick's time, most scientists argued that meteors in general were phenomena of weather-and were not originating in outer space. In fact, the word "meteor" refers to weather-based phenomena. In the 1860s the famous astronomer, Givanni Schiaparelli showed the connection between the appearance of Comet Swift-Tuttle (which orbits the sun every 120 years, approximately) and the increase in the number of meteors during the Perseid meteor shower. This comet-meteor connection helped prove that meteors were astronomical.

How Does Science Study Meteors? Scientific studies of meteor showers have changed over the years. Around the time of Herrick, researchers were attempting to document the existence of showers. This required that accurate records be kept that showed the number of meteors and their brightness during the night. Such recordings continue to be of scientific importance and are collected by the International Meteor Organization which coordinates meteor amateur work throughout the world. The North American Meteor Network trains meteor watchers in Mexico, Canada and the U.S. With the use of radio telescopes, meteor activity can be monitored during the day and in other conditions when visual observing would be difficult or impossible. These studies assist in developing descriptions of the orbits of comets and their debris. Since Schiaparelli's calculation of the Perseid meteor stream orbit in the 1860s, the orbit of this stream has been calculated more times than that of any other. Thousands of independent observations have shown that the Perseids are irregularly distributed in their orbit, resembling a "filamentary" structure. Also the meteors are on average brighter before the maximum of the shower than afterward. Approximately 45 percent of the visible meteors in this shower leave visible "trains" or smoky trails (visible from very dark sites or with binoculars). This is higher than the percent of trains from random meteors during early August, though exactly why this is the case is not clear.

Every Shower Party is a little different from its predecessor. Each combines "heavenly" and "earthly" elements into a new experience. No one who was there will ever forget the year a tractor in a neighboring field plowed on through the night, throwing up huge clouds of blinding dust; or when Davis's newest shopping center opened to the northeast of our site filling the sky with gala shafts of light from searchlights. Then there was the memorable year we were attacked by gigantic flying bugs -- the infamous "Perseid Bug Shower." Last year, we were "invaded" by a friendly army of TV newspeople from Sacramento (Channels 3, 10 and 31) interviewing attendees and broadcasting "Live at 10 and 11 p.m.!" They kept the bright lights turned off as much as possible. We always have a lot of fun, even when there aren't many meteors visible.
The most unusual party was held August 11, 1993. This shower was forecast to be one of the best nights for meteor showers in recent history Arriving at 6:00 p.m., two hours before the scheduled meeting, I was the seventh car in the small parking lot. By 8:00 the parking lot was packed and parked cars extended for half a mile or more down all the roads leading to the school. The large grassy playing field became a solid patchwork of blankets. I suffered a recurrent feeling of near panic when I began to consider what might happen to me if these people decided the evening was not "fun." Fortunately the sky was gorgeous and we saw many meteors.

Finding More Information on Meteors: Neil Bone's 1993 book titled simply Meteors is a good introduction to observing, as is Gary W. Kronk's earlier (1988) book, Meteor Showers, A Descriptive Catalogue.

Astronomy Club Meeting June 21 on Libra and meteor impacts. A clear, though cool and breezy night greated approximately 30 members to the Club's meeting on Libra, modelling meteor impacts, and making magnitude indicators. Instead of the usual slide show, attendees received handouts showing how the constellation Libra was taken from the "claws" of the older constellation Scorpius (the scorpion). The handout also showed an example of the types of land forms one sees when observing the Moon (from Antonin Rukl's Atlas of the Moon) This was used as a key to assess the types of structures we created by dropping pebbles into a tray of white flour which had been overlayed with a thin dusting of instant hot chocolate power. We observed rays and ejecta patterns and that the larger an object is and the faster it travels, the larger the crater it makes. We also reviewed the back of the handout that showed a picture of the night sky for the evening. We had several telescopes: an 8" reflector, a young member's new 4" f/10 reflector, the Granetts' 16" dobsonian and Alvin Huey raced in from San Francisco to set up his 16" dob for the crowd. It was fun to revisit the "old favorite" astronomical objects of summer as Vega, Deneb and Altair rose in the West. Thanks to all who came out to see the sky.

July and August Skies Over Davis. Our weather, say some forecasters, is now emerging from "el Nino" and will be transitioning to a "la Nina" phenomenon. Spring and early summer have been unseasonably wet and mild. What weather will mid- and late-summer provide? The constellations are much more predictable. The southern sky at night in July is dominated by Scorpius, the scorpion and its red "heart", the star Antares. In August, Scorpius "moves" westward, and the constellation Sagittarius, with its "teapot" asterism comes to dominate the southern sky. Try to find a dark site outside of town, look southward and study Sagittarius and Scorpius with binoculars. The center of our galaxy lies in Sagittarius, and in binoculars you can appreciate the density of stars and gas that lies in that direction.

Good news for evening planet watchers! Jupiter at last begins to be visible in the late-evening sky in August. It rises around 10:00 p.m. in mid-August. An hour or so later, Saturn makes its appearance in the eastern sky. Mars and Venus remain objects for early morning viewers, while Mercury teases us with a quick glimpse of itself above the western horizon in early July. On July 16th, the planet will be due west at 8:30 p.m. approximately 15 degrees above the horizon. Good Luck!

Your host, Dennis Smith

The Astronomy Club is hosted by Dennis Smith with the assistance of Tim Feldman and other eager astronomy buffs. The club is for everyone - adults, children, knowledgeable or ignorant. Come to listen, look and learn, or to share your expertise or experience.