Sky Roundup: August, 2007

Midnight Meteor Madness and the Eclipsed Moon

With Summer in full swing, families often look for astronomical activities to keep children entertained and engaged.  And individuals just wanting to contemplate the majesty of the night sky will get themselves outdoors to spend some quiet time under the stars.  Nature does its part by providing a couple of evening shows this month just right for the individual and for the whole family.  The date of August 12 marks the annual peak of the Perseid meteors, and, a total eclipse of the Moon will occur on August 28.

Shooting Star The annual Perseid meteor shower that peaks on August 12 often shows bright meteors with long tails that flash through the sky in an instant. (Image by Dirk Obudzinski.)

First, the Perseids.  Every year in mid-August the night sky lights up with nature’s own fireworks.  Bits of rock and dust collide at high speed with the upper atmosphere of the Earth, blazing across the sky in a fiery demise.  More than simply burning up in a flash due to friction with air molecules, a bit of rocky debris actually builds up a pocket of pressurized air in front of it as it rams into the atmosphere.  The pocket of air gets super-heated from the ram pressure against the debris, causing it to ionize and glow.  It is this glowing ionization consuming the rocky debris that we see as a bright trail across the night sky.

Often nicknamed a shooting star, of course meteors are not stars at all; rather, they are the detritus from the wake of a comet whose tail has passed through the plane of the Earth’s orbit.  As the Earth moves through this field of debris, the detritus rains down through our atmosphere, sparking a flurry of shooting stars, which astronomers call a meteor shower.

The comet that gives rise to the Perseid shower is known as Swift-Tuttle, named for its two discoverers who last viewed the comet in 1862.  Astronomers speculate that the comet orbits the Sun approximately every 130 years, with some drift in its orbital position.  Its last approach near Earth was in 1992; its next approach won’t occur until 2126.  Astronomers speculate that the comet enriches its past trails of debris as it passes near Earth, giving us scores more meteors to watch as the debris collides with the Earth.  It is on these occasions when meteor showers become more like meteor storms, and the sky is thick with shooting stars.

The name of the shower, as with any meteor shower, comes from the point of perspective from which the meteors appear to radiate.  In the case of the Perseids, the radiant, or the vanishing point from which meteors emanate, appears within the constellation Perseus, the Hero.  Though Perseus itself hasn’t risen yet for most observers in the early evening hours that the shower commences, it is indeed the radiant for the Perseids; most meteors leaving a long, smoky tail across the sky can generally be traced back to the relative location of Perseus still below the horizon.

In times past, comets and meteors were regarded as omens.  At one time, the appearance of a comet was thought of as unlucky, as a harbinger of impending doom; in other times, a comet was seen as the soul of a fallen leader migrating to an afterlife.  Meteors, too, shared both good luck and ill fortune.  Meteors were regarded as lucky if one could make a wish while the shooting star was still seen streaking across the sky; too, meteors were thought to represent one’s spirit passing to a next life or the birth of new life somewhere in the world. 

In several accounts linked to historical events thousands of years ago, the appearance of bright comets or of intense meteor storms may have given rise to widespread panic and raving madness, destructive thoughts and utter ruin.  It is very unlikely that the meteor shower this month will result in the apocalyptic collapse of civilization.

The Perseids build for a few weeks prior to their peak on August 12.  Observers can spot the occasional Perseid as early as July 23.  As days near to the peak, the number of meteors seen per hour increases for later hours of evening.  Approximately 50 to 80 meteors per hour may be observed during the shower’s peak. 

In 2007, the peak will occur late in the evening of August 12 through the wee hours of the morning of August 13, as after midnight the Earth plows into the bulk of the comet debris.  For this year, observers will have no interference from the light of the Moon as New Moon phase occurs on the same day as the peak.  For observing the most meteors, observers should venture to the countryside, away from city lights, and watch nature’s own nighttime spectacle. 

Deep Red Moon This is how the Moon can appear during a total lunar eclipse.  How will it appear on August 28?  Watch for it over Cleveland and see for yourself. (Image by Steve Rismiller.)

And that’s not all.  Nature also provides another grand display near the end of the month, namely, a total lunar eclipse.  The Earth will cast its shadow across the face of the Full Moon in the early morning of August 28.  The light of the Full Moon will diminish, and then be blotted out entirely.  This particular event will show the Moon centrally deep in Earth’s shadow, which may result in a very dark red, perhaps even blackened, appearance of the Moon in eclipse.  Most of North America will be able to witness some portion of the eclipse.  For those observers in the Cleveland area, the best time to observe, weather permitting, is just before dawn as the Moon will set in total eclipse.  Astronomers from the Cleveland Museum of Natural History will be on hand with telescopes set up on the grassy expanse of Wade Oval at 4 a.m. to view the eclipse.

Meteor showers and lunar eclipses are completely safe to watch and fascinating for all to view.  Stay out late enough, and if it’s not cloudy, you could experience a little midnight meteor madness at mid-month and see a total lunar eclipse near the month’s end.

Sky Roundup Almanac for Cleveland, August, 2007

August   5: Moon at Last Quarter
August  6: Waning crescent Moon just over 1° north of the Pleiades
August 12: New Moon; Perseid meteor shower at its peak
August 15: Mercury at superior conjunction, which means it’s hidden by the glare of the Sun
August 17: Venus at inferior conjunction, which, in this case, is hidden by the Sun’s glare
August 18: Spica, brightest star in the constellation Virgo, 2° north of waxing crescent Moon
August 20: Moon at First Quarter
August 21: Antares, brightest star in the constellation Scorpius, less than 1° north of Moon
August 28: Full Moon, total lunar eclipse

Questions or comments?
Please contact:  Roy Kaelin at 216.231.4600, x3405, or rkaelin@cmnh.org