A Shower of Comet Dust: Get Ready for the Perseids

August 2016  :  Dave Huestis

Some events by their nature require advance planning. Weddings, anniversary celebrations and vacations are just a handful of activities everyone has had to prepare for well ahead of the scheduled date. Well, astronomers have very unique sky events that we are aware of years or even decades in advance that we may wish to observe.

One of those spectacular events will occur just over a year from now on August 21, 2017. It is being dubbed The Great American Eclipse of 2017. This total solar eclipse will be visible along a 2,500 mile long track, at maximum only 68 miles wide, that extends diagonally across the United States from Oregon to coastal South Carolina. (See the following website for an interactive map: http://eclipse.gsfc.nasa.gov/SEgoogle/SEgoogle2001/SE2017Aug21Tgoogle.html.) The maximum duration of totality will be two minutes and forty seconds. I’ve known about this eclipse since I first became interested in astronomy, and like many of my associates, will make every effort to be within the path of totality.

Millions of people will have the opportunity to observe one of Mother Nature’s most beautiful astronomical events as the Moon completely covers the Sun and reveals our star’s ghostly corona and magnificent red prominences of hydrogen. Unfortunately here in Rhode Island we are quite far from the path of totality and will only see about two-thirds of the Sun covered by the Moon. So if you have a strong desire to be a part of this great experience, you must plan now, otherwise you’ll be sleeping in your car in a parking lot. Hotels within totality’s path are already booked, and rumor has it that some establishments are price gouging. I’ll be writing a lot more about this eclipse as we get closer to the date.

While the 2017 solar eclipse is a special event, perhaps once-in-a-lifetime for some people, there are many other sky happenings that appear with clockwork regularity. And though I do not have psychic abilities, I can predict what many amateur astronomers and casual stargazers alike will be doing on the night of August 11-12, 2016. If the skies are clear, sky enthusiasts will be looking towards the heavens to see shooting stars associated with the Perseid meteor shower blaze across the sky.

The Perseid meteor shower is the most widely observed meteor shower of the year. This ranking is because families are spending more time outdoors during the summer season, enjoying cookouts, camping, or any other assortment of late evening activities. And years ago when there were still a few drive-in theaters around southern New England, you could always glimpse quite a few Perseids while watching the movie screen.

Though the December Geminids are the more productive shower of the year for us in the northern hemisphere, locally colder temperatures tend to keep all but the die-hards inside warm homes. Too bad, because I’d rather try to stay warm than constantly swat at mosquitoes!

While much of the literature on meteor showers often states that the Perseids are fairly consistent, I beg to differ. More often than not it seems the Perseids fail to deliver a good display of shooting stars at the predicted time. It’s very frustrating for me. When I provide you the shower specifics in this column I have checked more than half a dozen sources before publishing a suggested time to maximize your chances in observing as many meteors as possible. (For most meteor showers that I write about I do try to spend a few hours observing them as well. One, because I never tire of watching them—and two, because I want to see how well the predictions come to fruition.)

However, though I am occasionally discouraged, if the weather cooperates you can be assured I will be out under the heavens scanning the sky for the annual shooting stars of August to perform well. Here’s what you can expect.

For 2016 the Perseids peak on a Thursday night (11th) thru the pre-dawn hours of Friday (12th). Unfortunately we will have to contend with a waxing gibbous Moon (first quarter on the 10th) that will set just after midnight. This situation is not entirely horrible, as the Moon and the radiant for the shower will be at opposite sides of the sky. Besides that point, the Perseids are usually best after midnight anyway.

The Perseids are so named because they appear to radiate from an area of sky, called the radiant point, in the constellation Perseus. Perseus is well up in the northeast sky after midnight. (See accompanying finder chart.) If you can locate a pattern of stars that looks like a sideways “M” or “W” (that’s Cassiopeia), Perseus is below it so you’re looking in the correct direction. You know you’ve seen a Perseid if you can trace the path of a meteor back to the radiant point.

Most of the Perseids one observes are no larger than a thumbnail as they plunge into our atmosphere at 134,222 miles per hour (37 miles per second) and disintegrate. The August Perseids, which occur around the same time each year, are the remnants of Comet 109P/Swift-Tuttle that were stripped off the comet’s surface and deposited in “streams” throughout its orbit about the Sun. When the Earth passes through a stream we experience a display of shooting stars.

You can expect to observe 60+ shooting stars per hour in a light pollution-free sky once the Moon sets, so choose your viewing location carefully. I expect the best viewing opportunity will occur between moonset and dawn’s early light, which begins around 4:15 a.m. EDT. For fun, and to stay alert, keep a mental, written or recorded count of meteors per hour. You should note an increase as the morning progresses. Also take note of the colors of the shooting stars. They are usually green, red or orange, and a few may become brilliant exploding meteors called fireballs. See a video of a fireball over Maine on May 17, 2016: http://www.golocalprov.com/news/huestis-fireball-over-new-england-tuesday-morning-was-bright-one.

If the weather does not cooperate or you are unable to observe on peak night, try your luck on the nights before and after. You won’t see 60 meteors per hour, but you may catch a couple of dozen or so. The best time to observe will still be between midnight and dawn’s early light.

Cross your fingers that the sky gods favor us with a decent display of meteors for the 2016 Perseid meteor shower. And if you happen to see a stationary meteor (think about it—it’s headed directly at you), don’t forget to duck!

While you do not require a telescope to observe a meteor shower, don’t forget to explore astronomical objects far beyond our protective atmosphere at each of the following facilities. Seagrave Memorial Observatory in North Scituate is open every clear Saturday night. Ladd Observatory in Providence is open every clear Tuesday night. The Margaret M. Jacoby Observatory at the CCRI Knight Campus in Warwick is open every clear Wednesday night. Frosty Drew Observatory in Charlestown is open every clear Friday night. Check the respective websites for open times.

Good luck and keep your eyes to the skies.