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Get ready for the Leonids

From The 2003 rendition of the annual Leonid meteor shower will be much more challenging to observe than in recent years and will demand good timing, proper site selection and some patience.
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The 2003 rendition of the annual Leonid meteor shower will be much more challenging to observe than in recent years. For most skywatchers, spotting shooting stars on Nov. 19 will demand good timing, proper site selection and some patience. Below are several observing tips.

FIRST, AN OVERVIEW of what to expect. Meteor showers may conjure an impression of a sky filled with shooting stars pouring down through the sky like rain. Such meteor storms have indeed occurred with the Leonids, such as in 1833 and 1966 when tens of thousands per hour were observed. In 1999, 2001 and 2002, less active but still spectacular Leonid displays occurred, with a few thousand meteors per hour being counted by many observers.

The 2003 version of the Leonids are likely to be far weaker than that, but still worth a look in part because some of the shooting stars promise to be bright, and the Leonids are known for producing a few stunning fireballs.

THREE DISPLAYS There are actually three Leonid displays expected this year. The first is due Nov. 13, when Earth encounters a trail of dust shed by the Comet Tempel-Tuttle in the year 1499. This Leonid display favors those living in central and eastern Asia and Australia.

Another burst of activity may come Nov. 19, when Earth interacts with a dust trail from the year 1533. A rate of up to 100 per hour is possible. Much of eastern and central North America will be in a favorable position to see this display, but many of the meteors are expected to be faint.

The best hope for significant Leonid activity may come from a component of the Leonid stream known as “the Filament,” also due Nov. 19.

The Filament is composed of the sum of numerous dust trails shed by Tempel-Tuttle over many centuries. It should take about a day for the Earth to fully pass through it. The greatest activity may come near 12:30 a.m. ET (5:30 GMT) on Nov. 19, highly favoring western Africa and western Europe, though the northeast U.S. and eastern Canada would also be rotating into position to see peak activity as well.

While hourly rates may only reach 50 from the Filament, many of these meteors could be bright and in more than a few cases perhaps even produce dazzling fireballs.

HOW AND WHEN TO OBSERVE Watching a meteor shower consists of lying back, looking up at the sky, and waiting. If they reach their full potential on the morning of Nov. 19, the Leonids will produce about one meteor sighting every minute or two for a single observer under a dark country sky.

Any light pollution or obstructions like tall trees or buildings will reduce the count considerably, so it is wise to select a viewing location in advance. Even a bright street light or porch light can affect the number of faint meteors you might see.

The hours after midnight are generally best for watching for other shooting stars, too, because before midnight we are riding on the back side of the Earth in its orbit around the Sun, whereas after midnight we are on the front or advancing side. It’s a bit like all the bugs smashing into a car’s front bumper versus the few that can be spotted out the back window.

After midnight the only meteoroids escaping collision are those ahead of the Earth and moving in the same direction with velocities exceeding 18 1/2 miles per second. All others we will either overtake or meet head-on. But before midnight, when we are on the back side, the only meteoroids we encounter are those with velocities high enough to overtake the Earth.

Therefore, on the average, morning meteors appear brighter and faster than those we see in the evening.

SPEED, POWER AND ODDITIES And because the Leonids are moving along in their orbit around the Sun in a direction opposite to that of Earth, they slam into our atmosphere nearly head-on, resulting in the fastest meteor velocities possible: 45 miles per second (72 kilometers per second).

Such speeds tend to produce bright meteors, which leave long-lasting streaks or trains in their wake.

Also, as Leo is beginning to climb the eastern sky near and before midnight, there is a fair chance of perhaps catching sight of some Earth-grazing meteors. Earthgrazers are long, bright shooting stars that streak overhead from near to even just below the horizon.

Earthgrazers are so distinctive because they follow a path nearly parallel to our atmosphere. The late-night hours of Nov. 18 will hold the most promise of seeing an earthgrazer as the Earth approaches both the Filament and the dust trail from the year 1533.

Most Leonids are caused by bits of stuff no larger than a sand grain. A few larger objects, perhaps as big as a pea or marble, sometimes create dramatic fireballs. These are so bright they can cast shadows, and their colorful trails often linger for several seconds.

COUNT THOSE METEORS Making a meteor count can enhance your enjoyment of a shower. And it is relatively simple. Just lie down on a long lounge chair or snuggle up in a warm sleeping bag. Using a pencil and watch, note on a clipboard whenever you see a meteor. Keep your eyes moving around and don’t stare too long at any one place.

Not all shooting stars will necessarily be Leonids. Other bits of space debris can race across the sky at any angle. Leonids can race out in any direction, but they are identifiably by tracing them back to a point of origin.

A Leonid is one whose path, if traced backward, intersects a point called the shower’s radiant. That spot is inside the curve of stars that marks the “blade” of the Sickle of Leo.

The Sickle begins rising out of the east-northeast sky after about 11 p.m. local standard time and is poised high in the south as dawn begins to break. That is why Leonid watching is generally best between midnight and dawn.

Write an “L” every time you see a Leonid.

Other “sporadic” meteors traveling in random directions may be seen about once every 5 or 10 minutes. These can be noted on your clipboard with the letter “S.”

SEMI-PRO COUNTING TIPS Meteor counts by amateur astronomers are the primary means used for keeping track of shooting star history.

To be meaningful to groups that specialize in meteor observing (such as the American Meteor Society, the International Meteor Organization, or the North American Meteor Network), your meteor count should conform to standard observing methods, which include:

Noting your sky transparency (the limiting magnitude of the faintest star visible to the naked eye to at least the nearest half-magnitude). Do so again if there is any change, such as if the sky becomes hazier or, conversely clearer and darker.

Mark the times in your notes for each hour or half-hour, as well as the starting and ending times and any periods when you might have stepped indoors to warm up or were simply looking away. Do not lump all the Leonids you have seen from a long session into one undifferentiated total. For example, don’t say: “I observed 80 Leonids during a two hour and 20 minute time frame.”

If two or more people are observing together, each should keep an independent count as if he or she were alone. As difficult as it may seem, try not to be unduly influenced by somebody who catches sight of a brilliant meteor in his or her section of the sky and screams: “Holy Mackerel! Did you see that fireball?”

More information about counting meteors and submitting your results is available from the web sites of the organizations listed above.

The 2003 Leonids will not match up to the performances of recent years. Yet compared to the two best annual displays (the December Geminids and August Perseids), this year’s Leonids could be categorized as “very good.” In fact, with bright moonlight hampering both the Geminids and Perseids this year, the Leonids could turn out to be this year’s best overall meteor shower.

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