Wish I may, wish I might…see a shooting star tonight. If increasing your chances for wishing on a falling star sounds appealing, then circle the nights of August 11th and 12th on your calendar and make a big list of wishes – for this is the peak of the Perseid meteor shower, when it’s possible to see a hundred meteors an hour. In fact, for 2016, a meteor “outburst” is predicted, which means that if you’re able to watch after moonset, from midnight till dawn on August 12, you could see as many as 200 meteors an hour.
Give yourself at least an hour of observing time, for these meteors in meteor showers come in spurts and are interspersed with lulls. Remember, your eyes can take as long as 20 minutes to adapt to the darkness of night. So do not rush the process. - Bruce McClure and Deborah Byrd, EarthSky
“Meteor” is Greek for “thing in the air.” Ancient Greeks used it to describe rain, sleet, hail, lightning and thunder; hence the term meteorology for the study of weather. Today, “meteor” refers only to shooting stars.
Meteors are the result of interplanetary debris meeting our outer atmosphere. Amazingly enough, the debris for most meteors we observe is about the size of a grain of sand. Entering the atmosphere at speeds of 260,000 km per hour, the particle is rapidly heated by friction. Though friction heats up the debris, it is not the source of the light. As the particle heats up, excitation of electrons releases photons of light, causing the momentary bright streak in the sky. If the particle is big enough, the streak becomes a train of light and we can observe a direction of travel for the meteor. Meteors that appear brighter than the brightest planets are called fireballs. Spectacular fireballs are produced by particles not much larger than the size of a marble.
Even fireballs usually vaporize completely before they strike earth. The vaporized debris condenses as dust and settles slowly, adding an estimated 10,000 tons of mass to earth each year. The occasional meteor that is large enough to strike earth still intact is renamed a meteorite. A few thousand meteorites have been found, yielding information about the origins of our solar system.
On a given night, a careful observer might see 10 meteors an hour, but at predictable times of year, meteor showers produce many more. Imagine placing a large elliptical hula hoop at right angles around a smaller circular one. The big ellipse is a comet orbit, while the small circle is the orbit of earth, with the sun as the focus for both. At one point, the comet path crosses the path of earth’s orbit. As the comet nears the sun, fragments break away. These cometary fragments follow along the orbital path of the parent comet, dispersing around the entire orbit over many millennia. Now the big ellipse has a haze of cometary debris that the earth must pass through once every year. Thus the annual prediction of meteor showers.
The Perseid meteor shower, seen best every August 12 or 13, is from the comet Swift-Tuttle. They are called the Perseids because they seem to originate from the constellation Perseus. Other good meteor showers are the Orionids in October, the Geminids in December, and the Quadrantids in January.
From Bill Cooke, head of NASA’s Meteoroid Environment Office:
Every time Swift-Tuttle goes around the sun, it deposits a trail of particles which we call a meteor stream. Over time, the gravitational influence of Jupiter and other giant planets (but mainly Jupiter) changes the particle orbits, and as a result, their close approach distances to Earth will vary. If the change for a given stream is towards Earth’s orbit, we may see greater than normal activity when our planet passes the trail's nodal crossing. This year Jupiter’s influence has moved the 1079, 1479, and 1862 [meteor] streams closer to Earth, so all forecasters are projecting a Perseid outburst with double normal rates on the night of August 11-12 [evening of August 11, morning of August 12].
Take yourself to an open area away from interfering light, gather your family and friends, lie back and keep your eyes open. You won’t have long to wait for nature’s magical fireworks display – and you may even have a wish come true.
"Field Notes" is produced by the Montana Natural History Center.
(Broadcast: "Fieldnotes," 8/7/16 and 8/12/16. You can hear the program on the radio Sundays at 12:55 p.m., Tuesdays at 4:54 p.m., and Fridays at 4:54 p.m., or listen via podcast.)
