Once again it's time for the annual Perseid show. The maximum rate
of the meteors is supposed to occur at our location during daylight hours
on August 12. However, the Perseid maximum is broader than the peaks
of some other meteor showers, so the night of Aug 11-12 should be a good
time for viewing. Because the new moon is on the 11th, this may be
the best time to see the Perseids in the last 38 years. If it's cloudy,
or if there's not much of a show, then try again the next night.
After our planetarium show on Aug 11, we will meet at the Double Diamond
Pavilion for a Perseid Watch. We had a good time watching the Perseids
there last year. Bill Baker will again have some comments on the
Perseids and meteor showers in general. (Barbara and I will be watching
from the extreme southwest of England the night after we see - we hope!
- the total eclipse of the sun. Will we be able to see any Perseids
ducing the eclipse???)
The Perseids originate from a swarm of particles orbiting the sun, mostly
the size of sand grains, thrown off by Comet Swift-Tuttle. These
particles enter the earth's atmosphere at about 37 miles per second.
Friction with the atmosphere heats this space debris to incandescence,
and the particles burn up, sometimes after leaving a long glowing trail.
The Perseids are all moving along essentially parallel paths, but they
appear to emanate from a radiant because of the earth's motion through
the swarm of particles. The situation here is similar to the appearance
of snowflakes in your car's headlights as you drive through a snowstorm
- an experience I often had in another life a few miles north on another
part of the planet.
The star chart shows the Perseid radiant at 2:00 AM on Aug 12. The
radiant rises about 10:00 PM in the NNE, and is in the NE at 2:00 AM the
time shown. When the radiant is just rising, half the meteors will
be hidden below the horizon. As the radiant rises higher, more meteors
are likely to be seen.
The best time for meteor watching is between midnight and dawn, as the
leading hemisphere of the earth intersects the swarm of particles.
Because of our perspective, the paths of meteors close to the radiant will
be short, since we see these paths more nearly head-on. The paths
that we see farther from the radiant will appear longer. On rare
occasions, it's possible to see a point-meteor, a meteor heading directly
toward us straight out of the radiant. A perfectly aimed point meteor
would look like a star. The longer paths that we see are those of
meteors passing beside or above us, or in a direction that would carry
them below us.
If you want photograph the Perseids, I would recommend 800- to 1,000-speed
color print film. Use a wide-angle lens, at least a 35mm focal length.
Mount the camera on a tripod and aim it at the radiant if you want to try
for a point-meteor. Remember to reaim your camera as the sky moves.
Take a series of 10-minute exposures. You could also mount a camera
piggyback on a scope with a clock drive and track the radiant. Good
hunting!
You can print a copy of this star
chart so you can take it outside.
