M A Y A Springtime Meteor Shower
Swift, bright meteors characterize the Eta (h) Aqaurid meteor shower which reaches its peak when the moon is out of the sky in the first week of May. The fast moving particles that create the Eta Aquarid meteors belong to one of the two annual showers related to Halley's Comet -- they share a similar orbit to that venerable nomad. The other shower associated with Halley is the Orionids, which peak in October.Last year moonlight interfered with viewing the Eta Aquarids, but this year conditions for the early morning shower are ideal. The lone complication in observing the shower comes about because the radiant rises only two hours before the onset of astronomical twilight. The radiant, the point in space from which the meteors appear to emanate, lies near the "Water Jar" asterism in the constellation Aquarius. This region remains low for most North American latitudes. Observers farther south get a better view over a longer period from the Southern Hemisphere, the Eta Aquarids rank as the top meteor shower of this year.
Calendar
Full Moon - May 4
Last Quarter - May 10
New Moon - May 18
First Quarter - May 26The brilliance of these meteors generates the major interest -- more than 40 percent leave persistent as they hit the atmosphere at speeds reaching 40 miles per second (65 km/sec). Although the peak of activity is predicted to occur on May 4, it pays to watch a few days either side of this date: In 1997 the peak occurred a day early. The peak is broad, giving almost a week a good activity above a zenithal hourly rate (the rate calculated for perfect observing conditions if the radiant were to lie directly overhead) of 30 meteors per hour. Smaller number of Eta Aquarids trickle in between about April 19 and May 28.
The flash of a meteor arises when a tiny particle of comet debris, typically no larger than a grain of sand, strikes our atmosphere at a colossal speed and instantly vaporizes. The visible, ionized trail is what we observe as a meteor.
When a shower occurs, streams of material plow into the atmosphere. Each particle travels on a parallel track; observers on the ground get a perspective effect of the meteors apparently radiating from a single point in the sky when their trails are traced backward to an intersection point, the radiant.
A radio aerial tuned to a station some 200 miles away will pick up reflections off the ionized trails left in the atmosphere by meteors. The sudden and brief improvement in reception of a normally difficult-to-receive radio station indicates the passage of a meteor often run significantly higher than visual rates, and Eta Aquarids are good shower to check this out. "Observing" meteor showers with a radio also has the significant advantages that observations can be carried out in daylight, and under cloud cover.
EDT
Celestial Calendar 2000
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