Every year, as the Earth traces its path around the Sun, our planet encounters several distinct clouds of orbiting debris, mostly small objects the size of pebbles, that enter our atmosphere and burn spectacularly – even a grain of sand glows brilliantly as it incinerates from the friction, and is brightly visible in the night sky, at least in areas isolated from urban light pollution.
These regular events are known as “meteor showers”, and when they occur the meteors will emanate, seemingly out of nowhere, from a patch of sky occupied by one or another of the constellations drawn within our culture’s astrological connect-the-dots consensus. The showers thus bear the names of their associated constellations; those that issue from the sky around Leo are the “Leonids”, those from Gemini are the “Geminids”, and so on. The relative intensity of the showers varies from year to year, depending upon the density of the debris clouds that are encountered, and some are more reliably spectacular than others. Those that plunge each summer from the direction of the constellation Perseus are among the most consistently impressive. The peak of this year’s Perseid meteor showers occurred just a couple of days ago.
I’d been hoping to catch a glimpse of them this year, but low cloud cover, and the intense 24/7 glow of a nearby Irving gas station, got in the way. Apparently, the availability of gasoline at every one of these ubiquitous outlets rates a light show akin to something you’d see on the Las Vegas strip:
Never mind. Various posts on YouTube captured the display. This’ll give you an idea, and the narration is hilarious:
In ancient times, meteor showers were viewed with both wonder and trepidation. They’re mentioned fearfully in the Bible, at least according to my interpretation, being described as celestial fire thrown earthward by the “beasts” of Revelation. This is from the famous passage at Revelation 13:
Then I saw a second beast, coming out of the earth. It had two horns like a lamb, but it spoke like a dragon…And it performed great signs, even causing fire to come down from heaven to the earth in full view of the people.
As seen from our vantage point, “beasts” – the animals that compose most of the constellations of the Zodiac – do rise up from the ground, cresting the horizon and rotating into view as the evening progresses, and many of them do indeed regularly cause fire to come down from heaven in full view of the people. It’s my belief that the mysterious authors of this very mysterious book of the New Testament were describing observed astronomical phenomena throughout, and the meteoric fire cast down by the beasts in the sky seems to have struck them as particularly portentous.
I wrote a whole book about all this, actually:
To us, meteor showers are merely beautiful, and we might ascribe the anxieties of our presumably primitive forebears to superstition and ignorance, but here’s the thing: the ancients may well have been on to something, and there’s a very good reason to view meteor showers with a mixture of wonder and dread. We now know, moreover, that none is more worthy of our darkest fears than the annual Perseids.
The various clouds of debris that the Earth encounters in its orbits aren’t just benign cosmic rubbish that happens to be laying around up there. They’re the detritus cast off by comets as they follow their own paths around the Sun, and if the Earth encounters these trails of cometary refuse, it can only be because our path intersects with theirs – they belong to the category of “Earth-crossers”. The Perseids are the remains of a comet now identified as “Swift-Tuttle” (comets are named after the stargazers who discover them), a very large object that follows an elliptical trajectory that takes it out past Pluto before it plunges back in towards the Sun, making a full a circuit roughly every 133 years.
Swift-Tuttle is often described as “the most dangerous object in the Universe”. All Earth-crossers pose a theoretical risk to the Earth, in that our planet might eventually find itself in the same place, at the same time, as any comet in an orbit that intersects ours, but it’s a very big solar system, and the odds of this happening are generally vanishingly small. Swift-Tuttle is different. It tends to cross our path at uncomfortably close proximity, and it’s so big, at 26 km across, and so fast, whipping by at relative speeds calculated to peak at something between about 40-60 km per second, over 150,000-216,000 km per hour, that were it ever to strike us it would surely cause a global extinction event the like of which we haven’t seen since a similar object wiped out the Dinosaurs 66 million years ago. The relevant Wikipedia article asserts that Swift-Tuttle would hit the Earth with 27 times the energy of the impact that we think ended the Cretaceous Period:
The exact trajectories of long period comets, which are basically great balls of ice mixed with rocks, are notoriously difficult to predict. Not only are they observed infrequently, forcing astronomers to scour historical accounts to try to piece the evidence together, but their paths are affected by the tremendous energy of the Sun, which pounds them with the particles of the Solar Wind and causes them to both heat and erode, spewing out particulates and geysers of gas at velocities that can produce enough thrust to cause their courses to alter. This is why comets have “tails”, which don’t always trail the objects, but point away from the Sun regardless of the direction of travel.
It’s thus impossible to be absolutely sure how close Swift-Tuttle will be coming to us during its next few orbits. It was reckoned a few years ago that it might actually hit us as early as a century from now, in 2126, but subsequent recalculations provide assurance that we’ll make it through that year’s close encounter unscathed. Current projections have us living safely for at least another few thousand years.
One day though, as things stand, we will make our rendezvous with this interplanetary weapon of mass destruction. Swift-Tuttle is an extinction missile on a course to wipe out most of the complex multi-cellular life forms on our little planet, and the Perseids, so pretty in the Northern skies each summer, are the calling card of an implacable, remorseless angel of death, content for the moment to be biding its time. When we stare up in appreciation of those little streaks of brilliant light, we are, in effect, finding footprints in our garden, left by an assassin as he cased the premises and planned the best way to sneak in to murder us in our sleep.
So it goes in a Cosmos indifferent not just to life, but to itself. In the meantime, I suppose we may as well sit back and enjoy the show. Maybe next summer I’ll find some field in a dark corner of the province, set up a lawn chair, and try to think happy thoughts, as usual. Here’s one: it’s quite possible that future generations will have the wherewithal to alter the orbits of comets and asteroids that threaten life on Earth. There will, after all, be plenty of advance warning. Maybe, for once, we can respond rationally to a scientific prediction of looming calamity.