The Night Sky Fell

The Night Sky Fell

Watching the sky on a clear, flawless night, one should see a "shooting star" about every ten to fifteen minutes. The shooting star is really a fragment of comet dust that, upon entering our atmosphere, encounters friction, causing it to burn up. For the most part these individual particles of meteoric dust were once part of a comet.

The nucleus of a comet is not really complex. It consists mainly of frozen gases with many bits of solid matter, all of which are weakly bound together. Because the binding is quite weak, a comet is easily pulled apart when approaching a large celestial body. Since most known comets have an orbit that stretches from one end of the solar system to a point close to the sun, their life span is, astronomically speaking, short.

When a comet approaches the sun, many pieces of the comet are torn away by the gravitational influence of the greater celestial body. These pieces continue to move along the path of the mother comet's orbit. An entire comet may in fact eventually be destroyed in this manner, but the remnant comet dust particles, which could number in the billions, continue to move through space in the original orbit. When the earth passes through one of these dusty trails, the comet debris enters our atmosphere and a meteor shower results.

The Biela Comet, discovered in 1827, had a very predictable periodic orbit that crossed the path of the earth quite punctually ever six— and three—quarters years. When the comet came into view in 1846, scientists were astonished to find that it had split in two. The two halves traveled like celestial sisters, each with head, nucleus, and tail. They reappeared for the last time in 1852, and since they were not seen again the Biela Comet was presumed lost.

The comet had apparently come too close to the sun, which initially caused it to split in two. Thereafter the gravitational pull of the sun was so great that both halves fragmented. The countless particles of what was once the Biela Comet continued along the same orbit. This was a trail of celestial dust that crossed the orbit of the earth on November 27, 1872, at about 7:00 P.M.

As the cloud of particles enveloped the earth, friction with the atmosphere produced the most spectacular meteor shower on record. The sky was crisscrossed with bright crackling streaks that "fell like snow." It was estimated roughly that more than 160,000 shooting stars flashed across the sky that night. To the superstitious it must have seemed indeed that the sky was falling.

From the book: 
Our Fascinating Earth