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15th November 1998

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The night of flaming stars

Watch out for the Leonid meteor sower Wednesday pre-dawn

By Ranjit T. Edward

Seeing it here

Billed to be the astronomy event of the year, the Leonid meteor shower, a spectacular display of shooting stars, is expected to cross our skies some time in the pre-dawn darkness of Wednesday (18).

Meteor showerMost of us are familiar with the sight of a sudden flash of light across part of the night sky, possibly followed by a lasting streak of light. A 'shooting star' or 'falling-star' they call it. Quite occasionally the 'shooting-star' is very bright, brighter than the stars, and sometimes appears to emit sparks or even break up into pieces. On rare occasions its passage can be heard as a roar or a series of remote explosions. The trail left by a bright 'shooting-star' may last for less than a second.

What we witness when we see this phenomena, is a small piece of interplanetary matter, called a meteor, entering the Earth's atmosphere and 'burning up' at a height of about 100 km above the earth.

When this piece enters the Earth's atmosphere, its friction against the layer of air around is so great that it just burns out. However if the particle is very large, it will reach the surface of the earth.

I don't always go to a lot of trouble to see a meteor. Most years you'll find me focusing on a star or a planet in my garden in the pre-dawn hours, counting whatever meteors that pass my way. Usually, that isn't very many. I would be lucky to see about 5 faint meteors per hour. But then, there are those very rare days when thousands of meteors per hour may just appear. And this is what is expected on November 17-18, when the Leonid Meteor Shower, billed as the most exciting astronomy event of the year is predicted to appear.

The Leonid Shower is repeated every year around this time. The name is derived as it seems to emanate from the constellation Leo.

At intervals of about 33 years, this display is inclined to be more than a mere spritzing of meteors. It is a veritable storm.

Why are meteor storms so uncommon?

The secret is in comets. Simply because comets are the sources of meteoroids. When a comet comes out of the deep freeze of space and enters the inner solar system, its surface is warmed by the sun. Part of its icy crust suddenly turns to vapour, which solar radiation blows off the comet's surface.

Like snow-encrusted cars barrelling down a freeway, comets leave in their wake a tenuous trail of ice, dust, and grit. When the Earth sweeps through this detritus, the particles burn up in our atmosphere, creating a shower of meteors. It is as simple as that!

The Leonids in particular are composed of debris from periodic Comet Tempel-Tuttle. This comet has a period of 33.18 years. When the comet makes a close approach to Earth, as it did in January this year, it brings with it a more consolidated trail of debris. Thus, when Earth passes through this debris stream, we see a greater display of meteors than usual. We might see a meteor storm. Leonid meteors have been observed for over a thousand Years, and sometimes this shower does produce storms.

On November 17, 1833, before dawn the sky over eastern North America became the tableau for one of the most spectacular meteor storms ever recorded. Within a few hours, over 200,000 were seen from a single location.

The return of the Leonid meteor shower is no doubt the major astronomical event of 1998. As mentioned before, the Leonid meteoroid stream is linked to the periodic comet 55P/Tempel-Tuttle. The comet was rediscovered on March 4, 1997. Comparing the 1998/1999 Leonid return with past events, we find that the encounter conditions are similar to those of 1966.

Although these predictions look quite accurate, we should definitely not rely on them and be prepared for the full range of activity at any location. Experts say this year's Leonid shower might be best observed over Japan and the Asian continent. This is encouraging news to us, in Sri Lanka.

Specifically, the midpoint of the peak time of the 1998 Leonid display is predicted for between 18 00 and 20 00 hours UT (GMT) November 17.

But part of the charm of meteor showers is that they are notoriously unpredictable! It's probably pretty certain that the counts will be lower this year than in 1966. Still, you will never know precisely when and where the most meteors will be seen. And, you never know how many meteors you'll see.

It's a misconception that you have to know the whereabouts of a meteor shower's radiant point, in order to watch this. It's true that the Leonid shower does appear to radiate from the "sickle" asterism of Leo—the backward question mark pattern representing the Lion's head. And it's true that this part of Leo clears the eastern horizon by midnight this time of year.

We have one thing to be thankful for. That old bugaboo of meteor showers — the moon — will be at its new phase at this time of the year. So this time it is not a problem.

Meteor watching is easy. You don't need (and shouldn't use) binoculars or a telescope—just your eyes. Plan to start your Leonid watch 18th and 19th early morning. Who knows what kind of a show will be on?

As the night gets older the shower's radiant (apparent point of origin) in Leo will be getting fairly well up in the east. The higher the radiant, the more meteors appear all over the sky.

Our only disadvantage will be the clouds and the rains that we have been experiencing these last few day. Both totally out of our control. Still, with a little support from the rain gods, we will have a good show. If the 17th works out to be a rain and cloud filled night, try the next, and the next day. Some kind of a shower will be seen.

Seeing it here

Sri Lanka is one of the best places for watching Leonids. Leo rises from the east at midnight (0000 Hrs). Sun rises around six in the morning. You can enjoy Leonids from 2 to 5 early morning local time (2 hrs to 5 hrs). Leonids will reach the maximum around 2 am local time.

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