Date: May 31, 2009
Title: Stars That Fell Like Rain
Podcaster: John Johnson
Description: This episode presents basic information on meteors and meteor showers. Watching the annual meteor showers is a great way to spend time with friends and family. Understanding the process that brings us these events can only add to the excitement.
Bio: John Johnson is a professional body piercer, hip hop artist, and amateur astronomer from Long Beach, California. He loves sharing his interest in astronomy with his friends and will talk about space with anyone willing to listen. John can be found outside his Long Beach apartment with his telescope almost any night with good weather inviting friends, neighbors, or anyone walking by to take a look at Saturn, the Orion Nebula, or any other object waiting to be discovered by someone unfamiliar with the universe.
Today’s sponsor: This episode of “365 Days of Astronomy” is sponsored by Joseph Brimacombe.
“Stars that fell like rain.” That’s how Chinese records from the year 687 BC describe the Lyrids meteor shower. Admiring the beauty of shooting stars is just one of the ways astronomical observation connects us with our ancient ancestors and the universe. Shooting or falling stars are the words we’ve used to describe this phenomenon since long before we had a scientific understanding of these events. Even today we still tell kids to make a wish when they see a shooting star. There’s something about seeing a shooting star whether by accident, or preparing for an annual view of your favorite meteor shower, that keeps us mesmerized by the experience. I think it’s the instantaneous and sometimes unexpected connection we have with the universe, space is coming to you. You didn’t see pictures in a book, on tv, or on your computer. It was a single moment in time that will never repeat exactly the same. That flash of light across the sky comes and goes before you know it. After millions or even billions of years in space, the smallest pieces of debris are meeting their end, crashing into the Earth’s atmosphere at 25,000mph or faster! For most, the result is a fine streak of light, for larger pieces, maybe a quick fiery burst, 50 to 75 miles above the Earth‘s surface.
But what is it that happened? Most shooting stars and meteor showers are the result of comets. So let’s talk about comets. The solar system was formed about 4.5 billion years ago. Left over debris composed mostly of ice and rock remains in regions at the farthest distances away from the sun, in areas called the Kuiper Belt and the Oort Cloud. Composed of rock and ice, many people call comets “dirty snowballs.” Occasionally after millions of years in orbit, some of these Kuiper Belt Objects get close enough to the outer planets like Neptune that gravity’s influence changes their path and they’re ejected from the solar system completely, or begin a new trajectory that can bring them in closer to the sun. Oort Cloud Objects can even be affected by other stars passing too close. Oort cloud and Kuiper belt objects colliding among themselves may have the same result, and a comet is born. As a comet approaches the inner solar system, the sun’s heat causes the comet to vent gas and dust. Force from the solar wind causes the comet’s tail to form and it now looks like the image we usually see in pictures. Some comets will return someday, some will leave the solar system forever, and some will be eaten by the sun. Comets that cross the Earth’s orbit will leave behind a stream of debris of mostly dust and very small fragments.
This stream of comet debris can remain in the Earth’s orbit for thousands of years, and predicting the dates of meteor showers is easy, as our planet travels right through clouds of comet dust annually. A point of interest is that the particles of dust that make up a shooting star are called meteoroids while they’re still in space. They’re meteors once they hit the Earth’s atmosphere and the largest pieces are meteorites when they survive long enough to hit the ground.
A quick search in a farmer’s almanac, online, or in any astronomy book will provide you with a list of dates and names for the many meteor showers we have every year. The Lyrids, Orionids, and Geminids are some of the most popular meteor showers. Another big one is the Leonids which happen in mid-November each year. This shower has been observed since 902 AD. It’s the result of comet Tempel-Tuttle that was discovered in 1865 on December 19 by Ernst Wilhelm Liebrecht Tempel in France and independently discovered 2 weeks later in the US by Horace Parnell Tuttle.
Meteor Showers are named after the constellations they appear to come from. When you view a meteor shower the bright flashes of light will streak across the sky in every direction and every part of the sky. But if you trace their path backwards they seem to originate from the same place. This location is called the radiant. We can associate the radiant with a particular constellation. For example, the Orionids, which peak around October 21st, radiate from the constellation Orion.
The stream of debris left behind from a comet’s tail is wider than the Earth, so shooting stars in any meteor shower can be seen in any direction as our planet passes through.
Any night of the year is fine for spotting a couple meteors. Just go outside and look up. Have a seat in a comfortable lawn chair or your sleeping bag. Take some snacks and fill your MP3 player with your favorite 365 Days of Astronomy pod cast episodes. Eventually you’ll find what you’re looking for. Of course the darker the sky the better. A good rule of thumb is to be about 20 miles from large cities to lessen the effects of light pollution. The phase of the moon may also help or hurt you. A bright or full moon can really light up the sky and make only the brightest shooting stars visible. But if you have a lot of clouds overhead it won’t matter where you are or what the moon looks like.
If the conditions are good and you’re going to spend the evening watching a meteor shower, get started around midnight. Before then, you’re on the trailing side of the Earth. In other words, you’re facing away from the meteor shower, like looking out the rear window of a car as it moves forward. We spin in the same direction as our orbit, and after midnight you’re passing through the debris stream head first. That’s when you can expect to see more shooting stars, and brighter ones as well.
The Quadrantids meteor shower on January 3rd is a popular one with an average of 40 meteors an hour under good conditions. And if you think that sounds like a lot, the Perseids in August can reach 80. Counting the number of meteors you see each hour is popular when viewing a shower with family and friends. Consider keeping records throughout the year and compare them with the years to come, and don’t forget to have fun. Once again, I’m John Johnson from JohnJohnsonOnline.com. I thank you for joining me today and for celebrating the International Year of Astronomy.
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365 Days of Astronomy
The 365 Days of Astronomy Podcast is produced by the New Media Working Group of the International Year of Astronomy 2009. Audio post-production by Preston Gibson. Bandwidth donated by libsyn.com and wizzard media. Web design by Clockwork Active Media Systems. You may reproduce and distribute this audio for non-commercial purposes. Please consider supporting the podcast with a few dollars (or Euros!). Visit us on the web at 365DaysOfAstronomy.org or email us at info@365DaysOfAstronomy.org. Until tomorrow…goodbye.