Sometimes called shooting stars, meteors are pieces of cometary debris and the occasional cloud of asteroid dust that burns up in Earth’s atmosphere. On an average night throughout the year, you can see several meteors an hour. These are caused by random specks of cometary debris, about 1-2 millimeters in diameter, that had the bad luck to be in the way as the Earth came barreling through in its orbit around the Sun.
But what causes these cosmic light shows that take place a few times a year like clockwork?
It’s All About the Orbits
While Earth’s orbit is fairly close to circular, like all the other major planets, the orbits of most comets are tilted off the plane on which the planets orbit the Sun. Also, the shape of their orbit is usually an extreme ellipse, like an elongated circle.
When the comet’s orbit around the Sun intersects Earth’s orbit, similar to the diagram on the right, the ice and dust that blows off the comet as it passes the intersection is left behind. Later, the Earth slices right through dust cloud as it crosses the same intersection.
A Speck By Any Other Name
You may have noticed that meteor showers have names.
The Perseid, Leonid and Geminid meteor showers are a few of the most recognizable. These names are derived from the constellations each shower appears to be radiating from every year as the Earth makes its yearly trip around the Sun.
To picture what “radiating” means as it applies to meteor showers, if you were to record it for the entire night, then play it back at the fastest speed possible, you might think a meteor shower looks similar to the snowflakes in a snowstorm if you were driving with your high beam headlights turned on.
The three showers mentioned above appear to emanate from the constellations Perseus, Leo and Gemini. They occur in August, November and December, respectively.
As of this writing, the next meteor shower coming up will be the Lyrids, which will be peaking on April 23, 2019. If you guessed that they appear to be radiating out of the constellation Lyra, you’d be right!
We’re Surrounded! – The Kuiper Belt and the Oort Cloud
Earlier, I mentioned that the orbits which comets follow are highly elliptical and tilted off of the orbital plane which the planets follow. Well, those tilted orbits can potentially come from any direction.
Beyond the tiny realm of the major planets, which huddle relatively close to the Sun, there lurk barbarians. The far outer reaches of the solar system are chock-full of potential trouble makers. The two regions listed below are the source of all the comets we see, as well as their debris, which, if their orbit instersects that of fhe Earth, sets the stage for meteor showers.
- The Kuiper Belt – An inner tube-shaped ring of small solar system bodies which orbit the Sun beginning just beyond the orbit of Neptune, at about 40 Astronomical Units (AU). These objects are leftover material from the formation of the Sun and planets 4.57 billion years ago and composed mostly of ice. They range in size from small chunks of ice to small worldlets, including Pluto, and the slightly larger dwarf planet called Eris. The Kuiper belt is believed to be the source of short-period comets, with orbital periods of 200 years or less.
- The Oort Cloud – A vast expanse of similar material as the Kuiper belt, the Oort Cloud is believed to begin at about 2000 AU, extending out to almost two light years from the Sun.This spherical domain is the source of long-period comets with orbital periods of longer than 200 years. But don’t let the diagram above fool you. If the Oort cloud were as dense as the picture suggests, we couldn’t see through it!
The Main Culprit – The Comet’s Dust Tail
This is what sets the stage for the sky to start falling… or rather, for things to start falling from the sky. If you’ve ever actually seen a comet, you’d see that it seems to just hang there; a bright ball with a fuzzy tail trailing off behind it.
Other than the rocky core, a comet is mostly composed of ice. Some scientists use the analogy of a dirty snowball, while others prefer calling it a snowy dirtball.
So, as the comet gets closer to the Sun and it’s surface heats up, jets of evaporated ice erupt from the comet and take some of the surface dust particles with it. This is what’s left in the Earth’s path to later become meteors.
Meteoroids and Meteors and Meteorites! Oh, My!
What’s more satisfying than giving a science nerd (like me) a wedgie? Watching him squirm when you use the following terms incorrectly!
- Meteoroid – A space rock (most commonly about 1-3 millimeters in diameter) traveling through space before it enters Earth’s atmosphere.
- Meteor – The bright flash of light you see as a space rock burns up in the atmosphere.
- Meteorite – A space rock that has survived burning up in the atmosphere and has hit the ground.
The Late Show is the Best Show
Now that you know where meteors come from and what causes meteor showers, all you need to do is plan ahead to get the best view!
Did you know that the best time of night to view a meteor shower is after midnight? At that point in the Earth’s rotation, your location on the surface is just beginning to face into the oncoming dust particles. Similar to when driving in the rain, you see more rain hitting the forward-facing windshield than you see hitting the side or rear windows.
So, if you plan on heading out to a dark location to watch an upcoming meteor shower, be sure to pack some energy drinks. Otherwise, you may end up sleeping through the best part of the show!
Mark Your Calendar!
Check it out! Whether you live in the Northern or Southern Hemisphere, the American Meteor Society maintains an accurate and detailed calendar of upcoming meteor showers and how bright the moon will be during the peak of the shower. (Full moon bad, New moon good!)
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