Sky & Telescope - August 2021 - 48

AUGUST 2021 OBSERVING
Celestial Calendar by Bob King
A NearPerfect
Year
for Perseids
Sit back, relax, and enjoy this
summer meteor spectacle.
T
he forecast couldn't be better.
When the annual Perseid meteor
shower peaks on the night of August
11-12, the Moon will be a thin crescent
and safely tucked in bed shortly after
the end of evening astronomical twilight.
With no extraneous light to mar
the view, this year's shower should be
one of the best. Up to 100 meteors per
hour will fl are from the darkest skies,
but 60-80 per hour is a more realistic
number for most observers.
As shown in the chart below, Perseids
stream from a radiant in Perseus, just
near the W of Cassiopeia. In the same
way parallel railroad tracks appear to
converge in the distance, meteors follow
parallel paths that seem come from a
CASSIOPEIA
Andromeda
Galaxy
Double
Cluster
Perseid
radiant
ANDROMEDA
PERSEUS
TRIANGULUM
Capella
Looking Northeast at 11 p.m.
48 AUGUST 2021 * SKY & TELESCOPE
Rafael Schmall took nearly 1,000, 120-second exposures over three evenings to create this
montage of the 2017 Perseid meteor shower. He used a Canon EOS 6D camera (set to ISO 6400)
and a 16-mm lens at f/2.8.
particular spot in the sky. Most meteoroid
particles are no bigger than a grain
of sand, with a few as large as M&M
candies. Each Perseid is a fragment shed
by Comet 109P/Swift-Tuttle during one
of its many trips around the Sun.
Every August, the Earth intersects
the comet's path and plows through it
at high speed. As each fragment slams
into the atmosphere at some 60 kilometers
(37 miles) per second, it glows
white-hot from friction and burns to
soot. At the same time, it excites (ionizes)
the air molecules along its path.
When those molecules relax back to
their previous, unexcited state they emit
light. Both the glowing, hot particle and
trail of ionized air are responsible for
the familiar and eye-catching meteor
streak. Picture an incandescent pebble
traveling 200 times faster than a jet
airplane at the center of a self-created
tunnel of luminous air. That's a meteor!
The best time to look for Perseids will
be on the 12th from about 2 a.m. until
dawn, when the radiant is highest in
the sky. But you'll see a modest number
as early as 10 p.m. on the 11th, even
with the radiant low in the northeast.
The later you stay up, the higher Perseus
rises and the more meteors you'll see.
Pleasant August weather often makes
it easy to stay up watching meteors all
night. Bring the kids, and make sure
you have comfortable lounge chairs
so everyone can relax while gazing
skyward. Dress warmly and cover up
with a blanket to keep the chill at bay.
Perseids streak all over the sky, so you
can face any direction you like. Lie back
and watch the constellations lazily drift
by carried by Earth's rotation as you
anticipate the next meteor fl ash.

Sky & Telescope - August 2021

Table of Contents for the Digital Edition of Sky & Telescope - August 2021

Contents
Sky & Telescope - August 2021 - Cover1
Sky & Telescope - August 2021 - Cover2
Sky & Telescope - August 2021 - 1
Sky & Telescope - August 2021 - Contents
Sky & Telescope - August 2021 - 3
Sky & Telescope - August 2021 - 4
Sky & Telescope - August 2021 - 5
Sky & Telescope - August 2021 - 6
Sky & Telescope - August 2021 - 7
Sky & Telescope - August 2021 - 8
Sky & Telescope - August 2021 - 9
Sky & Telescope - August 2021 - 10
Sky & Telescope - August 2021 - 11
Sky & Telescope - August 2021 - 12
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Sky & Telescope - August 2021 - Cover3
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