The Perseid Meteor Shower
Comets >
This week we’re headed for global collisions of non-lethal proportions!
This Friday night and Saturday morning we will experience a meteor shower
- the Perseids to be specific. Unfortunately, the might-as-well-be-Full
Moon will partially ruin the spectacle, but most of the Perseids are bright
enough to be seen through the blanched night sky.
So what is a meteor shower? Let’s use the Perseids as an example:
There is this comet called Swift-Tuttle, whose orbit around the sun happens
to intersect our own orbit. We drive through this intersection every year
on or about the 12th of August. Fortunately, we haven’t bashed into
each other–yet.
Swift-Tuttle, being a good little comet, naturally sheds dust and crud
throughout the centuries in its travels around the sun. This debris slowly
spreads out over the whole orbit of the comet. So even though we won’t
collide with the comet for a long time we do collide with its flaky waste
every year at this time.
Thankfully, the individual debris bits are small, sometimes pea-sized,
but almost never bigger than a grain of sand. However, when we slam into
these little grains of seemingly innocent comet crud, they pack quite
the punch, crashing through the atmosphere at more than 20 miles per second!
That’s about 50 times faster than a rifle bullet.
When these little guys hit the unsuspecting air molecules in our atmosphere
about 50 miles up, the air molecules get so heated up that they glow,
lighting up as the intruder races though. It’s the same thing that
happens when spaceships return to Earth.
On any given clear night you can see these stray, fiery critters about
a half-dozen times an hour. But during a meteor shower, when we cross
through the orbit of some comet, we can see about 10 times that many.
That, ideally, is what will happen Friday night and into the wee hours
of Saturday.
The
shower is usually best in the wee hours of the morning because that is
the time the Earth, turning on its axis, heads right into the debris stream
from the observer’s point of view. Imagine driving through a cloud
of locusts. The windshield, facing the swarm, will get plastered with
pureed hoppers, while the rear window will remain relatively unaffected.
The meteors you see most of the rest of the year are strays. Those occasional
"shooting stars" are from the asteroid belt or lost bits from
other comets.
Want to guess how often we’re hit daily, shower or not? Hundreds
of times? Thousands? Try over 20 million times! And though each meteor
has a typical mass of less than a gram, that adds up to more than 100
tons of meteor dust every day! Some of the dust you clean up off your
dresser came originally from somewhere out in the cosmos.
Late Friday night, dressed warmly and armed with bug spray and binoculars,
go outside and lie down. Don’t look in any particular direction;
they will appear randomly in any given part of the sky. The beauty of
the Perseids is that they are often intensely bright and leave long trails.
And don’t worry about getting hit by any of them. No meteor from
a shower has ever survived the flight and fallen all the way to Earth
(when they get the name "meteorite"). Their fluffy nature assures
they’ll burn up. Bottom line: you’re safe.
Until next time, clear skies and invigorating showers!
Mark Ritter is a high school astronomy instructor and can be reached at
ritter@firstlightastro.com. Images and movies related to this article
can be found at http://firstlightastro.com/icolumn.html
Posted by Administrator at 2000.08. 7 09:19 AM | Comments (0)
