Stargazing: The Perseid Meteor Shower
Image courtesy of Pixabay
A dark moon provides the perfect opportunity for spotting our best and brightest meteor shower of the year - the Perseids. Shooting stars have been darting across the heavens in small numbers for four weeks (I saw five of them in the space of fifteen minutes the other night) and are expected to peak on August 11, 12 and 13 when we might be able to see as many as 50 to 100 an hour.
The Perseids frequently leave trailing wakes of light and colour behind them as they shoot through Earth's atmosphere. They are also known for their fireballs - larger, brighter explosions that persist longer than an average meteor streak.
WHAT ARE METEOR SHOWERS?
Whilst stray bits of cosmic debris hit Earth all the time there are also regularly-timed ‘meteor showers’ when Earth ploughs into the trail of particles left behind by a comet or asteroid. These particles enter Earth's atmosphere at speeds of up to 130,000 miles per hour and vaporise into shooting stars.
Every year, from around July 17 to August 24, Earth crosses the orbital path of Comet Swift-Tuttle, parent of the Perseid meteor shower. Swift-Tuttle is a large comet with a nucleus 16 miles in diameter. It was discovered in 1862 by Lewis Swift and Horace Tuttle and three years later Giovanni Schiaparelli realised the comet was the source of the Perseids.
The point in the sky from which meteor showers appear to come is known as the radiant. The Perseids' radiant is the constellation Perseus the Hero, hence their name. In ancient Greek star lore, Perseus was the son of the god Zeus and the mortal Danae. It was said the Perseids showered gold across the heavens in commemoration of the time Zeus visited Danae.
Perseus is a constellation in the northern sky, with
Andromeda to its west and Cassiopeia to its north. Its best known stars are the yellow white supergiant Mirphak and thevariable star, Algol, colloquially called the Demon Star. The Perseids do not come from the constellation itself, but emerge from its direction.
Comet Swift-Tuttle has an eccentric, oblong, 133 year orbit that takes it outside Pluto’s orbit when farthest from the sun, and inside Earth’s orbit when closest to the sun. Every time Swift-Tuttle passes through the inner solar system, the sun warms and softens the ice in the comet, causing it to release fresh debris into its slipstream. Comet Swift-Tuttle will not reach its perihelion (closest point to the sun) again until July 2126.
VIEWING TIPS
The best displays are between midnight and dawn, although at times it is possible to see meteors from this shower as early as 10 pm. If you're really lucky you might spot an ‘earthgrazer’ - a long, slow colourful meteor travelling horizontally across the evening sky. Earthgrazer meteors are rare but memorable. Perseid earthgrazers appear before midnight, when the radiant point of the shower is close to the horizon.
If you don’t catch them over the coming weekend, there might be a chance to see the tail-end of the Perseids for another ten days, although they are renowned for building up gradually and stopping abruptly.
Give yourself at least an hour of observing time, as the Perseids come in fits and starts. Your eyes can take as long as 20 minutes to adapt to the darkness of night, so be patient.
A few of the meteors you glimpse might come from the Delta Aquariids – a slower and steadier meteor shower that rambles along from July 12 to August 23. The Delta Aquariids radiate from the constellation Aquarius, which means August meteors can be flying in two different directions at once!
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Copyright © Karen Meadows 2018