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That Time of Year Again
Comets >
You may have seen one of them already. They started arriving in the late part of July and most will show up with their friends in the wee hours of the morning this coming Sunday. They have arrived for their annual shower. No, it's not Uncle Bob and his family. These are the Perseid meteors.
But what are they and how do they get here. It's thinking cap time!
We'll start with a comet, but not that bright object with a 100-million-mile tail. That classic image of a comet exists for only part of its life. Most of its time is spent out in the dark, cold depths of the outer solar system. There a comet is nothing much more dramatic than what astronomers call a "dirty snowball."
These miles-wide piles of snowy schmutz began their lives as leftovers from the creation of the solar system, orbiting the sun often at distances way beyond Pluto.
Once in a blue moon one is tugged toward the sun by a passing star or by interaction with another heavenly body and it then begins a long (emphasis on long) journey in a new orbit which takes it into the inner solar system. Once they come within Jupiter's orbit, the sun can warm them up enough that things start happening.
The ices start to evaporate off and the once sedate snowball starts firing off geysers of water vapor. When this happens the dirty part of the comet sloughs off, too.
But the dirty stuff doesn't all just zip out into deep space, oh no! A lot of it stays close to home, traveling the same orbit as its parent.
After many, many years of this the comet develops a following, so to speak, of tiny little particles of crud, some leading the comet around the sun, some of it following. This tiny train of debris can stretch out for millions and millions of miles.
Now what if the orbit of our comet and its offspring just happens to cross the orbit of earth? That, my friend, means potential fireworks.
Imagine
being one of these tiny grains of comet stuff. You're sailing along, nearing
the sun in your orbit around the star, business as usual. Although you
can see your parent comet a b-zillion miles away, around you are a lot
of your fellow rejects, particles which suffered the same fate of cometary
banishment as you have.
Then you realize that that big blue planet, the third one from the sun that was always off in the distance on your other visits through, isn't so far away this time. In fact, as you pick up speed --- as all things do on their close approach around the sun --- you see you also happen to be speeding toward a collision with that blue rock.
Then it happens. Sadly, you both cross orbits at exactly the same moment. You speed directly into the planet's atmosphere traveling at over 20 miles per second. In the twinkling of an eye, your slam into the air, lighting it up in a brilliant flash --- and you vaporize. You were among the oldest and most well preserved "stuff" in the solar system and in an instant you are no more.
If you get a chance to see some the Perseid meteors, do. Particles that have strayed from the main trail will be smacking into us for a couple weeks before and after Sunday. But in the wee hours next Sunday morning we pass through the thickest part of the debris stream and then is the best chance of seeing some fireworks.
Until next time, clear skies!
Posted by Administrator at 2001.08. 4 08:18 AM | Comments (0)
