Though spectacular-looking as intense streaks of light shooting across a darkened sky, meteors are really little more than tiny bits of interplanetary dust and debris, or meteoroids , burning up as they collide with the Earth’s atmosphere. With meteor showers, our planet is passing through an entire stream of debris, often times left by passing comets and asteroids as they orbit the sun.
Depending upon the size and trajectory of a particular debris stream, as well as
our own planet’s orbit, the journey through can last anywhere from a couple of
days to several weeks, producing sporadic meteors at each end of the trip, and
peak nights of many meteors, or storms, as we pass through the thickest regions
of the stream.
Comets’ debris trails can extend many millions of miles and remain prevalent
for many hundreds of years. Each time that a comet passes, that stream becomes
thickened with new debris to temporarily produce more prolific showers, but
not necessarily in the years immediately following.
Again, it all depends upon the respective orbits of the comet and our planet.
For instance, with the Perseids, our planet currently passes through a
general debris field estimated at one-thousand years old; but in 2028, we’ll
pass directly through thicker debris left in 1492, thus more prolific showers
are predicted for that year.
The Perseids , the first shower positively identified with a comet, are
associated with comet 109P/Swift-Tuttle . This comet is a periodic comet of
129 years and its debris field is known as the Perseus Cloud. Swift-Tuttle
last passed our planet in 1992, producing peak rates of 200-500 streaks in
1993 and 2004. We’ll next see this comet pass our way in 2121 and likely
experience better showers in the year or two following.
Comet Swift-Tuttle 1992
Because meteor showers have been observed since long before their
Relationship to comets was known, meteor showers are named for the
constellation from which they appear to originate. Their specific origin point,
from within the constellation itself, is known as the “radiant.“
Knowing a meteor’s radiant is important to providing accurate counts of a
particular shower. For example, not every meteor you see this month will be
a Perseids. Not only is our planet nearly always passing through one debris
Trail or another, resulting in several showers each month, but we also
Regularly encounter random bits of interplanetary debris.
The Perseids’ radiant is complex, with the two most prolific origin points
appearing to be from around Eta Persei and the famous Double Cluster,
NGC 869 and NGC 884.
The Double Cluster in Perseids – NGC 869 and NGC 884
one of two primary radiants of the Perseids Meteor Shower
The Perseids’ duration, that time when our planet is passing through
Comet Swift-Tuttle’s stream, is from July 23 through August 22, with
this year’s peak, or maximum, predicted to occur on August 12 from
1130 UTC through 1400 UTC. Typically, the Perseids produces fifty to
eighty streaks per hour on peak night, but there have been some
surprise years with hourly peak rates as high as 200. This year’s
maximum hourly rate is predicted to be 100.
The best time to observe the Perseids is in the hours before dawn,
after the moon has set. You’ll find the constellation Perseus high on
your NNE horizon, just east of the Pleiades star cluster.