Arkansas Sky Observatory

Sultry August, known in the northern hemisphere for its blistering hot days and rapidly cooling nights....suggesting the crisp and rewarding glimpses into rich Autumn skies.....can be one of the most pleasant months of the year for the naked eye stargazer.

The air is usually quite calm and the nights are comfortably warm, but not too much so. After sunset and the last light of dusk turns to the deep inky black, the dark night sky becomes rewardingly rich in bright stars.

The bright band of light stretching from northeast to south - our Milky Way, consisting of millions of tiny stars just beyond the threshold of human eyesight, appears as a diffuse summer cloud suspended from the stars. Binoculars and small telescopes show the Milky Way not as a cloud but rather reveals thousands and thousands of these seemingly tiny stars, each a part of the vast spiraling system of our galaxy.

Just before dawn's light, the mighty constellation of Orion, the Hunter emerges far in the southeast. It is one of the most majestic of all constellations and provides the summer skygazer with a reminder of the glories of the night sky of winter.

To top off the fascination of August skies, almost every clear night the sky is streaked with bright meteors. There are no less than three (3) very prominent meteor showers which peak in August (the earth in its orbit actually overtaking a large mass of cometary debris from ancient comets slowly disintegrating from the energy of the sun).

Perhaps the finest meteor show of modern times occurs each August, emanating from the constellation of Perseus, which is low in our northeastern sky at dark. For the casual observer the Perseid meteors are the easiest to track back to their apparent point of origin in the sky.

A few Perseids can be spotted as early as July 25, and the darker the night sky is, the more that will be seen on each night. An interesting project for observers is to monitor the sky on each available night and simply make a count of the number of meteors that can be seen each hour. Slowly, as the month progresses, this count
should climb until around mid-August, when the maximum number of Perseid meteors is expected. By the night of maximum each year, you may have a few hours of very dark sky, without the moon, during which the spectacular display of Perseids can be enjoyed. Even if the moon makes its debut on the night of maximum (which it will NOT in 2002!), you should continue to monitor the sky because the number of meteors always goes up dramatically after midnight when the dark side of the earth plunges head-on into the meteor swarm during the second week of every August.

Based on my past observations, you should be able to spot about 25 meteors on the date of maximum from about 10:00 PM until 11 :00 PM and about 45 from 11 :00 PM until midnight (with a dramatic increase at about 11 :30). After midnight the true nature of the spectacular meteor shower can be seen, the fainter ones whipping across the sky like "falling stars." Because the rate of meteors after midnight is usually well in excess of 100, you can probably expect at least 45 to 50 bright meteors per hour in spite of moonlight, since this shower contains more bright meteors than dim ones.

By 6:00 AM local time, the radiant of the Perseid shower is directly overhead from northern latitudes during mid-month, at which time you can expect the maximum number of meteors. These bright yellow Perseids frequently leave trails of smoke, and many times they explode midway, which results in several bright meteors flying away from the central body. The Perseids are apparently debris left over from the deterioration of a comet first seen in 1862.

This comet, known as Swift-Tuttle, has an average period of 120 years, meaning that it should return (if there is anything but debris left of it) in 1982. Interestingly, the comet and the Perseid meteors never pass close to any planet in our solar system except the earth. The result is that the orbit is stable, and the objects in that orbit are predictable. Early in the 20th century, E.J. Opik estimated that the total mass of the material in the Perseid meteor stream might be around 1 billion tons, but later he revised that estimate upward to 10 billion tons, and even again up to 200 billion tons! His estimates were based on the number and the frequency of the meteors that
observers had recorded. Even though it appears that his estimate is fairly accurate, however, the comet itself could not have been that massive. The modern theory is that the Perseid meteors do not come from that single comet but from several comets that sweep through the same orbit, each deteriorating a little each time it passes the
sun.

We do not know how long the debris that accounts for the Perseids has been in space. The earliest recorded observations of this shower were made by the Chinese in 36 A.D. when the shower peaked, not in August as it does today, but on July 17. From 714 A.D. until the present year, the Perseids have been recorded every year.
It does appear, however, that the large swarm of particles is decreasing in number because each year the total number observed drops off somewhat.

In addition to the Perseid meteors each year, observers will be treated to "interlopers" during the vivid Perseid display from the KAPPA CYGNID meteors, discovered by
Chinese astronomers in 1042 and which peak each August 20th with up to 20 meteors per hour on dark, moonless skies.

Another, more intense, meteor shower that peaks each August 30-31 is the ANDROMEDID meteors which appear to converge at a point in the constellation of Andromeda; in 1885 nearly 15,000 meteors per hour were seen from this remarkable meteors shower, fragments of the once-famous BIELA'S Comet which split into two major fragments after its close passage to the sun in that year. From dates that I have located, it seems that the Andomedid meteors can be seen either August 31, October 3, or possibly as late as November 14 on any given year.

In addition, much practical astronomy can be learned and much valuable information concerning our solar system can be determined through YOUR observation of meteors and meteor showers. Indeed, many principles of data reduction of meteor observations require the application of physics (meteor velocity), trigonometry (determinations of orbit and height), and chemistry (temperatures and composition).

But of greater interest: the observation of meteor showers yields yet another face of astronomy that perhaps is NORMALLY NOT available to the lay public: the opportunity for an observer to spend an enjoyable evening under relaxed conditions viewing one of the most spectacular phenomena of the skies....and, if you like.... while collecting valuable data of importance to the professional astronomer.

It is both fun and rewarding for even untrained observers to monitor meteor showers with a "purpose" in mind....even if that purpose might be only to share what was seen in 2002 with others years from now! Meteor observations should be made under conditions as dark as possible, away from city lights, and preferably when the moon's light is absent from the sky (see my forecast for the 2002 Perseid shower below!). As for equipment, the observer needs only a comfortable position (such as that provided by a lawn chair, blanket, or sleeping bag), a set of star charts that can be written on, a flashlight covered with a red filter, and some method of keeping accurate time (preferably a short-wave receiver to pick up WWV time signals or a watch set to an accuracy of 1 second by WWV found at http://nist.time.gov/ .

Because the light of most meteors is faint, it is essential that the observations be made when the moon is near new phase, or when it is absent altogether from the sky. Perhaps the most valuable equipment any meteor observer can have is the friends who share in the excitement of the meteor hunt and provide the good times and companionship necessary to make it through the late hours of night. I n addition, the buddy system works quite well in meteor observing.

The sightings of meteors increases toward the morning hours because it is after midnight that an observer's location is aimed in the direction of the earth's path about the sun. The earth is moving in space through its solar orbit with a velocity of 18.5 miles per second; during the evening hours only meteors with a velocity greater than that velocity can overtake the earth in its path and be seen by the observer. Those meteors that make head-on collisions with the earth's atmosphere are missed by the observer on the evening side of the earth. However, during the morning hours (i.e., after midnight) the observer is facing INTO the stream of meteors, right at the point the Earth's atmosphere is colliding with them in its solar orbit.

Remember that you are NOT seeing a "falling star"... Far from it: Meteors are but tiny fragments (nearly all less than the size of a walnut) that are burning up from intense
friction as they pass through the Earth's air at up to 20 miles per second. Most vaporize completely and many will leave a fine smoky train in the wake of the fiery plunge.
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PERSEID METEORS IN 2002

The point of the sky where the Earth intersects the debris cloud of Swift-Tuttle, and hence the "collision point" for our atmosphere as it plunges into the Perseid stream, is located astronomically at:
Right Ascension: (RA) = 04 hours 04 minutes
Declination: (DEC) = + 58 degrees

This point of the sky's coordinate system where the Earth "hits" the moving/orbiting stream of Biela bits moves slightly from year to year, and in some year - as with all meteor showers - the Earth may go through nearly more central than others, hence more density of debris and more meteors seen....provided the light of the moon does not interfere! This year - 2002 - the August moon is a thin waxing crescent moon, seen early in the evening in post-dusk skies. It will set very shortly after dark, allowing one of the most "moon-free" Perseid Peaks on August 12-13 in recent times!

Remember, however, that most meteor showers will peak after about 11 p.m. local time and the numbers will increase dramatically during morning hours on August 13. It has been my experience with the Perseid Meteors that the best time for observations begin about 1:30 a.m. and last until about one hour before dawn (typically about 3:15 a.m. local time from mid-northern latitudes). This year should be no exception.

Because of the recent (1992) close pass by the Earth of Comet Swift-Tuttle, recent years for cometary debris have been favored for spectacular shows of Perseids; however, this expected outburst has NOT happened.

This year, the experts are forecasting perhaps 60 meteors per hour during peak on August 12-13; I am going out on a limb this year and increasing that number by one-third, to about 90 meteors visible to the naked eye by a single observer each hour. Remember also that there are two other dominant meteor showers that will be sending these celestial streaks our way as well. The Perseids after midnight on the 13th will emanate from a point on the far northeastern horizon and streak in ALL directions across the sky; if you could trace them all backwards, you would see that they all converge on the same spot in the constellation of Perseus. The Kappa Cygnid meteors, on the otherhand, will be coming from a point nearly directly overhead at the same time....from Cygnus. The Andromedid stream is always one to watch, but it is a bit early for these at the peak of the Perseids; nonetheless, about a dozen or so should be seen, traced back to their origin point rising nearly due east about 1 a.m. local time.

Although the peak is scheduled for late on the evening of August 12 and throughout the morning of August 13; since the thin waxing crescent moon will have SET by the time the meteors reach their peak (after about 11 p.m. local time, increasing into the morning hours), this year's shower is one of the most favorable in recent years. This is a long duration shower, with many (as many as two dozen per hour) being seen from August 9 through the 20th; during the PEAK, expect to see at least 60 or more (perhaps double that number!) around 2 a.m., streaming from the constellation of Perseus, high in the northeastern sky. Best views are afforded by positioning your feet to the EAST and facing directly overhead.

In both professional and amateur astronomy circles, there will be a major effort for observers to actually monitor the MOON during the Perseids via CCD, digital and visual means to look for flashes that may indeed be part of impacts of Perseid meteorites against the lunar surface. During last year's November LEONID meteor shower, lunar impacts were actually seen and recorded with video camera equipment as the Earth-Moon system passed through the very densest central part of the Leonid cloud.

Observers will need to monitor the moon obviously very early after sunset on the evenings of August 10-15th for any signs of lunar impact, but because of the unilluminated nature of most of the moon as we see it during that time, conditions WOULD be favorable for lunar impact sightings. Scientists are predicting that most such possible impacts will/could be on the north-central portion of the moon. On November 17-18 in 1999, actual lunar impact from a LEONID meteor was reported by Brian Cudnik, a Texas amateur astronomer, this appearing as a flash of nearly "starlike" light on the dark side of the moon.....the reported impact was NOT a figment of Cudnik's imagination: it was recorded by noted occultation observer/planner David Dunham via a simple video camera and five-inch telescope!

Recording Perseid meteors via a camera can be fun, exciting, and add much punch to a very fine night of observing. To do so requires only a "fast" 35mm film camera, a good digital camera, or video camera. All equipment must be adjustable to "manual" settings and capable of long-exposure photography. In ALL cases, set the camera lens to "wide open" or the smallest "f/number" on the camera's lens. Likewise, ALL cameras must be set to INFINITY focus for perfect star and meteor images. Do not change or attempt to focus once started. The 35mm and digital cameras MUST have a time or "bulb" setting and cable release or remote shutter button for effective use.

In addition, make sure that all cameras are firmly mounted on a tripod or riding "piggyback" on a telescope; the former allows for he streak of the bright meteor to apss across the star trails (long arcs of light) as the Earth rotates and records the star images as trails left behind. The longer the exposure, the longer and more curved appear the star trails. If riding on a tracking telescope, the star images should be pinpoint, with constellation outlines clearly identifiable, but the bright meteor (4th magnitude and above, typically) will streak across these fields of view.

35mm Camera - select a camera with a wide angle or standard lens (the wider the better). At a very dark sky site, let the camera shutter stay open for at least 7-10 minuts time. If you have just started your exposure and a bright meteor streaks through where you "thought" you are aimed, do NOT stop your exposure...the star images need some time to record so that you will have a record of what star field the meteor passed through! For film, select either a fast (ASA 400 or above) film. Black and white images are captured well on Kodak's Tri-X Pan film, while color film is available up to speeds 3200 ASA which is idea under dark sky contitions. Fugi slide film ASA 1600 or 3200 is preferred for this. Because most Perseids are reddish and deep yellow, these films are suitable to rapidly capture the full spectrum of the meteor.

1) exposures are typically limited to about 16 seconds maximum with a few cameras able to record slightly longer; 2) during the exposure, the camera will also record electronic/digital "noise" which shows up as false starlike images throughout the image....the longer you go, the more noise evident; 3) digital cameras EAT power and batteries will not last the entire night; if using a digital camera make sure that you turn OFF the small LED view screen if possible; this will assist in conserving power.

Video Camera - Most good VHS and Digital video cameras today use low-light CCD light enhancers to guarantee capture of meteors to about 2nd magitude and certainly the fireballs and their associated trails from the Perseids. Since these cameras are recording "real time", merely mount on a tripod firmly, open the lens up to maximum (again, "smallest 'f/stop'") and focus at infinity....start the camera and let it keep going!

Whether you are observing from a lawn chair with friends and family, using the eyes and imagination to enjoy the Perseid Meteors or set up for sophisticated timing and recording via some imaging system, there are a few basic rules to remember for the best results!

1) To start observing meteors visually, recline with your FEET to the Northeastern sky and you gaze concentrated directly overhead; you will see more meteors there than if you look straight at the radiant....the further from the radiant, typically the brighter the meteor will become;

3) For success with either visual or photographic methods, do NOT be tempted to shut down if someone shouts: "..wow! There went a big one!" behind you. The tendency is to immediately stop your exposure and turn the camera in that direction.....not a good idea. Just leave everything where you have it set; eventually your time will come.

4) Do not expect to see every bright meteor that comes our way...thatis why it is a great idea to share this experience with others and have several observers all of whom are facing different directions with a bit of sky overlap between them!

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