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History of the Leonid Meteor Shower     

People have always seen shooting stars, but this natural phenomenon has only been understood for about 150 years. In ancient and medieval times, shooting stars were believed to be strictly an atmospheric phenomenon, like the weather. Consider that the science of studying the weather is called "meteorology."

Traditionally, a "meteor" could be a rainbow or a "sun dog" or any other type of halo effect, in addition to shooting stars. For centuries, meteor showers were believed to be evil portents, along with eclipses, comets, auroras and just about anything else that was unusual in the sky.

In modern times, the Leonid meteors had been sighted and described by many scientists. The shower of 1799 was observed by Andrew Ellicott, the famous surveyor who layed out Washington DC and established the western boundary of Pennsylvania. According to Ellicott, "the whole heavens appeared as if illuminated by skyrockets."

The Leonids splashed into history on the night of November 12, 1833. On this night, a storm of Leonid meteors was seen all over eastern North America, from Niagara Falls to the Deep South. Some modern estimates place this event at 100,000 meteors per hour, almost 30 per second!

Many published accounts of this event describe the fear and trembling that accompanied this celestial outburst. According to one account, "No wonder that many, calling to mind the vision of St. John the Divine, when 'the stars fell unto the earth, even as a fig-tree casteth her untimely figs, when she is shaken of a mighty wind,' felt awestruck, and imagined that the day of wrath was come." Though the Second Coming did not happen the next morning, the meteor storm of 1833 is often credited with precipitating Christian revival in America during the 1830s and 40s.

One scientist who observed the 1833 meteors was Denison Olmstead, a physics professor from Yale University. Olmstead noticed that all the meteors appeared to radiate from the same place in Leo. Other scientists determined that this point in Leo was the same general direction toward which the Earth was moving on this date. This led to the conclusion that these meteors were caused by the passage of the Earth through a ring of dust and debris in space.

In 1866, 33 years later, two astronomers named Tempel and Tuttle discovered a comet in orbit around the Sun. It was calculated that this comet had an orbit such that it would revolve around the Sun once every 33 years. And then the next November, another spectacular meteor shower was observed radiating from Leo.

From these observations, it was concluded that the November meteor shower was actually the result of the Earth's passing through the tail of Comet Tempel-Tuttle. It was concluded that the meteors of November, 1799 were also caused by the same comet. Reviewing old records, a pattern emerged of notable meteor showers occuring in November, every 33 years or so.

In this way, the Leonids were identified as the first regular, predictable meteor shower. Since that time, many other regular meteor showers have been identified and associated with the orbits of other comets. For example, as we discussed in the August Update, the Perseid meteors are seen every year in August. The Perseids had been observed for centuries as "The Tears of St. Lawrence," a Christian martyr whose traditional feast day coincides with the meteor shower.

Nowadays, astronomers are certain that meteor showers are the result of the passage of the Earth's through a trail of debris left behind by the passage of a comet. In general, such as with the Perseids, these meteor showers are annual events. However, there is a strong tendency for meteor showers to be better than average in years after the passage of the associated comet.

In the case of the Leonids, the annual showers are every weak most years, maybe 10 meteors per hour. And every 33 years, the Leonids tend to explode in a veritable storm of exceptionally bright shooting stars.

In most meteor showers, the parent comet tends to leave a wide trail of debris, evenly distributed through space. In this way, the Earth takes a long time to pass through the meteor stream, and only a few meteors are seen per hour. But the shower can last for several days, and be seen by people all over the world during this period.

However, Comet Tempel-Tuttle apparently leaves behind a very narrow but dense trail of debris in space. So unlike most meteor showers, the Leonids have a very narrow "peak" in which the meteors can be seen. When Earth passes through, a lot of meteors can be seen for only a very short time, maybe less than an hour.

This is good and bad. It's bad because you have to be in just the right place on Earth looking at just the right time to see the shower. If you're an hour too early or too late, you can miss the fireworks altogether. But it's good because if you do happen to be looking at just the right time, the meteors zip one after another, filling the whole sky with bright streaks.

In the current predictions, two peaks are predicted. One peak will favor European observers. The other peak will favor North Americans, and that's the one explained above. These two peaks are based on the passage of the Earth through two separate comet trails, left by two separate passages of Comet Tempel-Tuttle.

However, these comet predictions are often incorrect, since many variables must be taken into account. In fact, the Leonid cycle has not always followed a perfect 33 year pattern. For example, a Leonid storm was predicted for 1899, and this didn't happen as predicted. Astronomers believe this may result from the orbit of the meteor stream being perturbed by the gravity of the huge planet Jupiter.

Nonetheless, the Leonids did perform as hoped in 1933 and 1966. However, the 33 year storm predicted for 1999 was a complete fizzle. The predictions were refined based on observations in 1997, 1998, 1999 and 2000. Much to *my* amazement, the Leonids did finally deliver the goods in 2001. So now the experts have even higher hopes for 2002.

Have the astronomers actually learned things about the Leonids in the last five years? Or is this year's prediction fraught with guesswork as in previous times? One thing about the Leonid meteors is that they always teach prideful man that he doesn't know as much as he thinks he knows about God's wondrous cosmos! On that note, I would encourage everyone to take a chance on this year's Leonids, but always remember the classical warning for smart shoppers down through the centuries: "Caveat Emptor" -- let the buyer beware!

For more information about topics from Classical Astronomy, please check out Signs & Seasons, a homeschool astronomy curriculum!

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