24Oct2015

When Rocks First Fell From The Sky

View Post Imagine a rock falling from the sky … and not knowing that it’s a meteorite.

On November 7, 1492, people around the Alsatian city of Ensisheim heard an explosion, accompanied by crashes of thunder.

The air lit up with fire as fear and terror reigned. A smoky flash streaked, screaming, through the sky, hurtling toward Earth at a sharp angle. The source of the chaos — a celestial stone — finally slammed into a wheat field on the outskirts of the town.

The only direct eyewitness to this unusual event, it seems, was a young boy. He proceeded to lead the stunned residents of Ensisheim to the charred-but-shiny rock, an object whose impact had carved a hole in the ground that was more than three feet deep.

The people assumed it had been sent from God. They also assumed it might be an omen. The Austrian emperor Maximilian I, who happened to be in Ensisheim at the time — adding, no doubt, to the superstitions — ordered residents to expose the rock at the local church. Chaining the object on holy ground, it was thought, would mitigate any evil it might bestow on the town.

We were not so confused by the meteorite that hit Russia this morning. We knew what it was — for the most part — and knew what it meant (also for the most part). We recorded its impact through our Digital Age version of word-of-mouth: smartphones and blog posts and tweets and videos and gifs. And yet the chaos in Russia this morning — the chaos that comes from a flaming space-stone, falling from the sky — was perfectly presaged by the chaos experienced in Ensisheim.

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Meteorites have always been objects of fascination.Bettmann/Corbis

In his History of Siena, the Italian priest Sigismondo Tizio pieced together accounts of the meteorite from Ensisheim residents, accounts sent through both pamphlets and word-of-mouth. This is how he described the scene [pdf] that played out in the meteorite’s wake — a scene that was strikingly different from, and yet strikingly similar to, the one that played out in the Ural Mountains this morning:

At this point there has to be mention of the immense portent which was seen this year in Germany: for on the seventh day of November [1492], near the city of Ensisheim and the village of Bauenheim above Basel, a great stone fell out of the sky, triangular in shape, charred, the color of metallic ore, and accompanied by crashing thunder and lightning. When it had fallen to earth it split into several pieces, for it had traveled at an oblique angle; to the amazement of all, indeed, it flattened the earth when it struck.

Other contemporary accounts of the meteorite — a small one, fortunately for the people of Ensisheim — would describe the thing, rather appropriately, as a “thunderstone.” They would also describe the “gruesome thunderbolt and long lasting roar” of the object as it hurtled through the sky, marveling at the crater it produced in the earth — one “half a man length” deep. The Swiss humanist Johann Bergmann von Olpe would claim that the sound of the meteorite’s screaming path could be heard as far away as Switzerland.

And in retrospect, the stone would seem to be sent from the heavens not merely as a kind of cosmic gift, but also as an omen of a changing world. Following the arrival of the thunderstone, Tizio would notice [pdf], Columbus would arrive in the Americas. Italy would be invaded by France. Europe would be struck by an outbreak of syphilis. Tizio reported the Ensisheim event, the scholar Ingrid Rowland notes, “knowing already than invasion, war, and disease followed its arrival.”

So the people of Ensisheim did what most of us would do in the presence of a spectacular object: They tried to take some of it for themselves. They began to chip off pieces of the stone — celestial souvenirs — until the local magistrate stopped them. Officials, wanting to get the rock to the local church, gathered a group of strong men, got a cart, and transported the thunderstone to Ensisheim.

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What remains of the Ensisheim meteorite today (Wikimedia Commons)

Today, though, we benefit from the crowd’s frenzy: Fragments of the Ensisheim stone have now found their way to museums around the world. The primary rock, however, just over 120 pounds in weight and now a flat gray in color, remains in Ensisheim — a permanent resident of the Regency Palace, built by Ferdinand of Austria in 1535. The thunderstone, so mysterious and terrifying to the people who saw it fall from the sky, is now encased in glass. Source: The Atlantic

How high up are meteors when they begin to glow?

Meteors are usually dust particles left behind by comets – bits of debris that enter Earth’s atmosphere from space. At what altitude do these meteors – sometimes called “shooting stars” or “falling stars” – become incandescent and begin to glow? That can vary.

Meteors become incandescent – or glow – almost as soon as they hit Earth’s atmosphere. Some meteors such as the Perseids in August burn up in the atmosphere at about 100 kilometers – or 60 miles – above Earth’s surface.

Other meteors such as the Draconids in October fall to 70 kilometers – or about 40 miles – before they heat up enough to glow and vaporize.

The difference is that the Draconids are much slower meteors than the Perseids. So the height in the atmosphere at which a meteor begins to glow depends on its arrival speed.

There are a dozen major meteor showers every year – and many more minor ones. Here are some meteor arrival speeds:

Leonids: 71 kilometers per second
Perseids: 61 kilometers per second
Orionids: 67 kilometers per second
Lyrids: 48 kilometers per second
Geminids: 35 kilometers per second
Fall Taurids: 30 kilometers per second
Delta Leonids: 23 kilometers per second
Draconids: 23 kilometers per second

By the way, the length of a meteor’s path across the sky doesn’t depend entirely on the meteor’s arrival speeds. It depends mostly on the angle at which the particle of dust slices through the atmosphere.

If the particle arrives at a low angle, it enters the atmosphere more gradually, heats up more slowly, and cuts a longer swath across the sky than if it barrels in at a steep angle.

The size, composition, and density of the dust particle probably also affect the length of the path – but scientists still aren’t sure exactly how. Source: Earth and Sky

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