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"The time to look is during the dark hours before dawn on Tuesday,
August 12th," says Bill Cooke of NASA's Meteoroid Environment Office
at the Marshall Space Flight Center. "There should be plenty of
meteors--perhaps one or two every minute."
And when we say August 12, we mean that morning … not that night.[local daylight time]
These typically fast and bright meteors radiate from a point in the
constellation Perseus, and, like all meteors in annual showers, they
cover a large part of the sky. The Perseids are considered by many
people to be the year’s best shower when the moon is out of the way
during the shower’s peak. This year’s moon is not quite out of the
way during the Perseids, but there is a window for meteor-watching in
the hours before dawn. The first quarter moon comes on August 8, but
full moon is not until August 16. On the morning of the Perseids’
peak, the moon sets around 3 a.m.
The Perseids were one of the most exciting and dynamic meteor showers
during the 1990s, with outbursts at a new primary maximum producing
EZHRs of 400+ in 1991 and 1992. Rates from this peak decreased to ~
100 — 120 by the late 1990s, and in 2000, it first failed to appear.
This was not unexpected, as the outbursts and the primary maximum
(which was not noticed before 1988), were associated with the
perihelion passage of the Perseids' parent comet 109P/Swift-Tuttle in
1992. The comet's orbital period is about 130 years, so it is now
receding back into the outer Solar System, and theory predicts that
such outburst rates should dwindle as the comet to Earth distance
increases. However, additional predictions suggested 2004 — 2006
might bring a return of enhanced rates ahead of the usual maximum,
and in 2004 a short, strong peak happened close to that anticipated
pre-peak time, though activity seemed to be roughly normal in 2005,
and the 2006 return was badly moonlit and poorly-observed.
An average annual shift of +0°05 in the solar longitude of the `old'
primary peak had been deduced from 1991 — 99 data, and allowing for
this could give a possible recurrence time around 16h40m UT on August
12 (λsol = 140°21), if so a few hours after the most probable
maximum, that of the 'traditional' peak always previously found,
given above. The timing of a tertiary peak, not seen in IMO data
since 1999, would be around λsol = 140°4, 21h30m UT on August 12.
While recent observations imply only the 'traditional' peak is liable
to recur in 2008, observers should be aware of these additional
timings as possibilities, and plan their efforts accordingly, just in
case!