Summer Meteor Shower - presented by Science at NASA.
It's summer. School's out. Camp fires are crackling, marshmallows are roasting,
and fireworks are exploding in the night sky. Those fireworks are the Perseid
Starting in late July and continuing through mid-August, scores of meteoroids
fly out of the constellation Perseus. They cross the starry Milky Way, bisecting
the heavens with vivid streaks of green or yellow light. Fireworks, indeed!
The source of the display is Comet Swift-Tuttle. Every 133 years the huge ball
of dirty ice swings through the inner solar system and leaves behind a trail of
dust and gravel.
At the moment, Swift-Tuttle is far away, but its debris is nearby, littering the
July and August part of Earth's orbit. When our planet passes through the debris
zone, specks of comet-stuff hit the atmosphere at 140,000 miles per hour, and
disintegrate in flashes of light.
Swift-Tuttle debris zone is so wide, Earth spends weeks inside it. In late July
when our planet first enters the outskirts, Perseid rates are low. A camper
peering out the door of his or her tent for an hour might spy only a
half-a-dozen shooting stars. That's a pretty show, but the real excitement takes
place in August. On the morning of August 11th through 13th, Earth will pass
through the heart of debris zone. During the dark hours before sunrise, meteor
rates could soar - well - meteorically, to more than a hundred per hour. August
11th, 12th and 13th are the dates to plan your summer camping trip
There's just one problem - the Moon. The Moon is full on August 13th, so it will
be glaring brightly just as the shower reaches the peak. Many of the fainter
Perseids will be overwhelmed by moonlight. It is not a disaster, however,
because some Perseids are fireballs, and they will have no trouble piercing the
The debris stream of Comet Swift-Tuttle consists mainly of very tiny meteoroids.
These miniscule pieces of comet dust produce meteors of ordinary brightness,
easily overwhelmed by the Moon. Fortunately, the debris stream is also spiced
with larger chunks, the size of golf balls, baseballs, and so on. When these
bigger pieces hit the atmosphere, they turn into fireballs that you can see
right through the moonlight. You might spot only a few during a long observing
session, but even a single fireball can make the whole camping tip worthwhile,
burning an incredible streak into your collection of good summer memories. Enjoy
your summer - and the Perseid meteor shower.
For more summer science blockbusters, please visit science.nasa.gov.