June 20, 2018

Astro-Event: The Perseid Meteor Shower.

This week sees a yearly summer astronomical event that may be termed “The old faithful of meteor showers;” the Perseid meteors. Other showers are often fickle, on and off events, but the Perseids routinely perform with zenithal hourly rates around 60 per hour or about one swift moving meteor per minute. Like the Mars email hoax, the Perseids also have a knack for generating a media frenzy around August, forever disenfranchising hoards of would be astronomers with promises of “the meteor storm of the century!” every year…

but it is knowledge and information that has driven you, the sophisticated blog reading public, to our humble door. The Perseids come from a radiant positioned on the Perseus-Cassiopeia border, which is placed high in the northeast in the early AM hours for those in the middle northern latitudes. Their parent body in Comet 109P/Swift-Tuttle, and the average incandescent meteor trail that you see is caused by a particle not larger than a grain of sand. You’ll see many more meteors if you watch in the early AM hours, as you are positioned on the side of the Earth facing forward into the meteor stream past local midnite. The forecasted peak arrives around 8:00 PM EDT on the 12th, and the good news this year is that the waxing crescent Moon will be safely out of the viewing zone.  This time frame favors the Central Asian region, but the maxima could hit several hours early or late. This shower also arrives around prime camping season, when it’s pleasant to lay out and observe. Be sure to pack bug repellant, a blanket, and perhaps a favorite sky watching beverage. Want to maximize how many meteors you’ll see? Here are some quick and easy tips;

-          Find the darkest skies possible.

-          Observe with a friend or two and watch in different directions.

-          Find a spot with a clear horizon.

Meteor observing also allows you to do real science; simply count how many meteors you see for a given hour from your location. Groups like the American Meteor Society always welcome data, as the trail of meteor debris isn’t always completely known. It may be possible that you just happen to be the sole observer at a given longitude that isn’t clouded out and just happens to witness an outburst! In fact, the Perseids have been picking up in the past few years, producing >100 per hour. Not quite storm levels (usually stated as +1,000 ZHR) but a never the less, a good show!

This week’s astro-term is Audible Meteors. This is a highly controversial phenomenon. Over the centuries, there have been reports of hisses, pings, and popping noises heard during bright fireball sightings. These have generally been dismissed as observer bias; our brain may say such a bright event should have an accompanying sound, the thinking goes, and promptly inserts one. There is some mounting evidence, however, that such an event may have some basis in scientific fact. What’s truly weird is that most audio meteor events happen near-simultaneously with the sighting; not only do meteors tend to occur at an altitude of 50 miles or so where the atmosphere is too thin to propagate sound waves, but the sound itself would take a fair amount of time to travel to the observer. An alternate theory was first purposed by Havey Nininger in his book 1934 Out of the Sky. He noted and purposed that the plasma trail of a bright fireball may be capable of producing Very Low Frequency radio emissions in a range of about 1 to 10 kHz. These could be transferred into localized electrophonic sound via nearby conduits such as telephone wires, antennae, or even trees or blades of grass. His theory was largely dismissed until revived by Colin Kealy of the University of Newcastle, and Japanese observers actually managed to catch and record this phenomenon in 1988. I personally recall hearing a distinctive “hissing” like water on a hot stove following a particularly bright Perseid meteor I witnessed as a kid. Do keep an ear out for this fascinating phenomenon. Catching it on video with accompanying audio would be quite a feat!

Comments

  1. Gerhard says:

    Great not on “electrophonic sound”. This phenomenon might explain an interesting experience I had about 20 years ago while watching the persieds with my brother-in-law. Standing outside the porch, over-looking the lake, we spotted a particularly brigt fireball. Simultaneous with the meteor’s passage accross the sky on of the children’s toys, with a wind-up music box inside, played several notes. We were stunned at the coincidence! However, if the loosely wound spring, a spiral of flat steel inside the mechanism, vibrated slightly due to the effect you describe. I could see how that might be just enough to overcome the slight amount of friction keeping the spring from unwinding fully, allowing it to play a few more notes. Pretty Cool! Thanks.

  2. David Dickinson says:

    You’re welcome; I had a similar experience with a Perseid sighting as a kid… heard a definite “sizzle” sound afterwards. Contraversial, but definitely something to it!

Trackbacks

  1. Astro-Event: The Perseid Meteor Shower. : Astro Guyz…

    I found your entry interesting do I’ve added a Trackback to it on my weblog :)

  2. [...] This post was mentioned on Twitter by David Dickinson, Rob Keown. Rob Keown said: Nice discussion of audible meteors in @astroguyz Perseids blog post: http://bit.ly/cBuhYF [...]

  3. [...] keep an ear out for an even stranger phenomenon, as bright meteors are sometimes accompanied by a hissing or crackling sound. Long thought to be a psychological phenomenon, a team of Japanese astronomers managed to catch [...]

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