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A fish-eye view of Perseid meteors in 2016 as seen from West
Virginia. (Image credit: NASA/Bill Ingalls) |
Perseid meteors have already begun to fall, promising to
astonish skywatchers later this month.
The Perseid meteor shower will peak on August 12th, just
four days after the new moon on August 8th, so dark skies should be ideal for
the annual display, which is one of the most reliable displays of
"shooting stars." This is in stark contrast to next August, when the
meteors will coincide with a full moon.
The meteor shower's peak will be in the early morning hours
of August 12 till August 14, but it will last for roughly two weeks, from July
25 to August 18.
The moon will set about 10:30 p.m. local daylight time on
the evening of August 12. For watchers in the Northern Hemisphere, the show
should peak later that night, especially when morning twilight begins. The
Perseids should peak for 12 hours or so, centred on the time when the sun's
ecliptic longitude is 140.0° to 140.1° (equinox 2000.0), or Aug. 12 from 3 to 6
p.m. EDT, according to the International Meteor Organization's (IMO) 2021
Meteor Calendar (1900-2200 GMT).
Eastern European observers are in prime position for the Perseid meteor shower, but North Americans aren't far behind. A single spectator under dark, clear sky may see 60 shower members every hour in theory, but observers with exceptionally dark skies frequently see much more.
Because it is a celestial highlight that can be enjoyed
without telescopes or other equipment, the Perseids are particularly appealing
for introducing the people to astronomy. When planning a public outreach event,
keep in mind that choosing a very dark location free of bright lights, haze,
and smoke can significantly increase the quantity of observable meteors.
At the peak of the Perseids, these meteors appear to diverge from a point known as the "radiant," which is located near the famed Double Star Cluster in the constellation Perseus' northern portion. The radiant rises higher into the sky in the northeast as the night unfolds, until the break of dawn signals the end of watching.
When night falls in the United States, the radiant is so far
north that it is visible above the horizon for most of the country. As a
result, some Perseids can be seen as early as the first hour of observation,
while significantly fewer meteors appear before midnight, even on the night of
the shower's peak.
Meanwhile, for locations south of the equator, including as Australia, New Zealand, and South Africa, the radiant is always low or below the horizon, resulting in few, if any, Perseids.
Meteors that appear near the radiant — in Perseus and the
adjacent constellations of Cassiopeia, Andromeda, and Auriga — have
foreshortened courses, but those that appear further away will be longer and
quicker.
The world's safest fireworks
The Perseids are notable for having many bright and fragmenting meteors with fine long-lasting trains, and they seem white or yellowish. The shower is caused by the debris of Comet Swift-Tuttle, which rounds the sun every 130 years on average.
When the comet approaches the sun, as it did in 1992, it
leaves a trail of small particles along its path. In mid-August, the Earth
passes close to the comet's orbit, interacting with these tiny particles of
comet material, which slam into our atmosphere at a speed of around 37 miles
per second.
Friction releases the kinetic energy of particles in short-lived flashes of light, despite the fact that most of this trash is no larger than grains of sand. The energy released per gramme of meteoroid mass vastly outweighs the energy efficiency of even the most powerful human-made explosives.
A slightly larger particle, such as a pea or pebble, can provide the illusion of a "shooting star" as bright as Jupiter or even Venus, while a meteoroid the size of a child's marble can grow into a dazzling fireball and blaze through the heavens with a brilliance approaching that of a full moon. It's dubbed a bolide if it silently explodes in flight, as it sometimes does with deathly cold materials abruptly heated to nearly 1,000 degrees Fahrenheit (540 degrees Celsius) in the span of a heartbeat.
Although such brilliantly luminous objects are few and far
between, it only takes one to make a night of skywatching worthwhile.
My favourite Perseid sighting was one that I didn't witness.
It happened while I was on a cruise ship in the Mediterranean, where I, along
with many of my fellow passengers, was looking for Perseid meteors. For a brief
instant, the entire deck of the ship was lit up as if a strobe had gone off. We
all whirled around to see a little blob at one end of an incandescent contrail.
What had just happened was obvious: a fireball had terminated in a blast of
light, leaving a twisted and deformed vapour trail that took nearly a minute to
fade away.
Viewing tips
Make sure you're comfy before seeing the Perseids. Stretch out in an insulated sleeping bag or, better yet, on a long reclining lawn chair wrapped by a large blanket instead of standing around gaping at the sky (and risking a stiff neck).
Expect the actual temperature to be significantly lower than
what your local weathercaster forecasts: Even if the air is just somewhat wet,
sitting near to the fast cooling ground might cause you to become rather cold.
In addition to layers, bring some snacks and a drink with you (but not liquor,
for that will impair your alertness).
Allow your eyes to acclimatise to the darkness when you
first go outside; after approximately 20 minutes in the dark, your pupils open
up like wells, catching four or five times the light they normally do. You'll
see more stars and meteors the longer you're out in the dark. Cover the lens of
a flashlight with red cellophane if you're using one, because dim red light has
a lower impact on your eyes than white light.
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