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Leonid Meteors on November 17.

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Leonid Meteors.
Leonid Meteors on November 17: Image credit: NASA.

The Leonid meteor shower will be making an appearance on November 17, 2003, and it might be an impressive show. These meteors are the minute dust trails of Comet 55P/Tempel-Tuttle which flash in the sky as they strike the Earth's atmosphere. In past years, the Leonids have been very impressive, sometimes thousands of meteors have been seen. Astronomers aren't sure how many will strike the Earth this year - it could be anywhere from a couple an hour to several hundred per hour. The best views will be in Europe, but the rest of the world will still get a show if they watch the skies after midnight.

It's back! After exceptional displays in recent years, the Leonid meteor shower will appear under dark skies November 17, 2003. Although no one knows for sure what the shower has in store for us, estimates range from a few meteors up to hundreds of meteors per hour at the peak.

Predicting meteor rates, particularly for the highly variable Leonid shower, is akin to estimating the number of snowflakes that will fall on an area of ground. You simply can't know until it's all over. And in the case of the Leonids, only observers outside will find out what happens.

The remarkable activity seen during the past few years came about because Earth crossed through regions that the shower's parent comet, 55P/Tempel-Tuttle, had visited. This year, the timing of Earth's passage across the comet's orbit favors observers in Europe. They should see the shower's peak before dawn on November 18. For North America, the peak arrives the previous evening, although the best views still should come after midnight. light from the Last Quarter Moon interferes somewhat, but the brighter Leonids should shine through nicely.

Mythology and finding Leo

The Leonids are named after the constellation Leo the Lion. If you trace all the meteor trails backward, they would meet within the boundaries of that constellation. In Greek and Roman mythology, Leo represents the Nemean Lion, whose slaying was the first of Hercules's twelve labors. To find Leo in the sky, first locate the Big Dipper in the northeast. Poke a hole in the bottom of the Big Dipper's bowl. As the water runs out, you may hear a mighty roar as the water falls on the back of Leo. In 2003, Leo is even easier to locate. Simply look for the Moon in the early morning hours of November 18, when the Last Quarter Moon will be in the center of the constellation. Adding to the spectacle, the planet Jupiter will be shining brilliantly just to the lower left of the Moon. Jupiter will appear as the brightest starlike object in the sky.

What are meteors?

Meteors are small particles of rock and metal that Earth encounters (runs into) during its orbit around the Sun. In space, these particles are called meteoroids. When they burn up in Earth's atmosphere, we observe bright streaks called meteors. If they survive the fiery passage through our thick blanket of air and land on Earth, they are called meteorites. No meteorites are generated from meteor showers - the particles are too small.

All meteor showers are caused by comets. As a Comet swings around the Sun, heat from the Sun vaporizes the ice in the comet, releasing small particles (meteoroids). Sometimes the orbit of this debris crosses Earth's orbit. When our planet runs into this stream of particles, we experience a meteor shower.

The Leonid meteor shower is caused by Comet 55P/Tempel-Tuttle. This Comet was discovered in 1865 by Ernst Tempel and in 1866 by Horace Tuttle. The Comet itself is about 2.5 miles (4 kilometers) in diameter and orbits the Sun during a period of slightly more than 33 years. When it makes its closest approach to the Sun, the Comet also passes close to Earth's orbit. This last happened on February 28, 1998. The encounter with the debris stream from Tempel-Tuttle lasts several days, but the most intense part of the encounter typically lasts only two to three hours.

Leonid meteors are fast (they move at 35 to 40 miles per second), and some leave smoke trails that can last a number of seconds. Many Leonids are also bright. Usually, Leonid meteors are white or bluish-white, but in recent years, some observers reported yellow-pink- and copper-colored meteors.

Observing the event

To see the meteors, you'll need a clear, dark sky. Dark means at least 40 miles from any large city. No telescope is required. In fact, the naked eye works best. Take a lawn chair, cookies, fruit, and a non-alcoholic beverage. (Alcohol interferes with your eyes' dark adaptation as well as your visual perception of events.) Most importantly, dress warmly, preferably in layers, because Leonid-watching involves no movement or exercise. You'll be either sitting or standing, and - because it's November - you will get cold.

Usually, the best advice for meteor-spotters is to go out after midnight during the showers. This is when your part of Earth faces the same direction as the planet's orbit around the Sun. Earth, therefore, is running into the meteor stream. This year, however, because of the times of the shower's peak and moonrise, a better plan is to begin observing at dusk on Monday, November 17, and keep watching until the cookies run out.

After sunset, face east and look one-third to one-half of the way up in the sky. Glancing around won't hurt anything. After moonrise, turn around so you are facing west (away from the Moon) and look overhead.

Photographing meteors

The Leonid meteor shower is not only a wonderful event to observe visually but also a wonderful shower to photograph. On a non-shower night, it's difficult to photograph meteors because they can occur in any part of the sky. Because meteors move so quickly, they don't register well on film. With the Leonid shower, however we expect many bright meteors throughout the night.

You will have more success photographing meteors under a dark sky because the background glow will be lowest. Low background illumination allows you to expose the film for longer intervals of time, increasing the chances of capturing meteors on film. Select a camera that allows you to take time exposures, a cable release to minimize vibrations when you open the shutter, and a tripod to steady your camera. Set the camera's lens wide open (the smallest f-stop on the lens), and set the focus to infinity. Use fast film - ISO 400 or higher. Whether it's colour or black-and-white film is up to you. Expose each frame for ten to twenty minutes. Good luck!

For the most up-to-date astronomy information and beautiful astronomical images, be sure to check out astronomy magazine and Astronomy.com.

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