Today, a comet approaches. The University of Houston's
College of Engineering presents this series about the
machines that make our civilization run, and the people
whose ingenuity created them.
Halley's Comet appeared in the sky
when Mark Twain was born in 1835. The comet moves in a
seventy-five or seventy-six-year orbit, and, as it neared
Earth once again, Twain said,
I came in with Halley's Comet... It is coming again
... and I expect to go out with it... The Almighty has
said, no doubt: 'Now here are these two unaccountable
freaks; they came in together, they must go out
together.'
Sure enough, he died on April 21, 1910, just as the comet
made its next pass within sight of Earth. And we hear
echoes of Shakespeare:
When beggars die, then are no comets seen:
The heavens themselves blaze forth the death of
princes.
But the orbit of Halley's comet specifically mocks the
human lifespan. I find a strange
song in an 1858 book of French songs:
"The Comet of 1832". Since that was three years before Halley's Comet,
the song-writer may've made a mistake. Or he may be
referring to a different, or even to a fictional, comet.
The song begins,
God is sending a comet against us
We shall not escape this great impact
I feel our planet crumbling already...
And it ends,
Go quickly to confession you timorous souls
Let us be done with it, the world is old enough
...
The world is old enough.
Halley's Comet was named after Edmund Halley, who
realized that several earlier comets were one and the
same. Then he calculated its narrow elliptical orbit. The
comet rides in from the outer fringe of the solar system,
makes a tight turn around the sun (inside the orbit of
Mercury), and then sling-shots back out, far beyond
Neptune. Halley predicted the comet's return in 1758, but
he didn't live to see it. Many older comets turned out to
be previous sightings of this one. It was seen just as
the Normans set out across the English Channel to conquer
England.
The nucleus of Halley's comet (like that of any comet) is
a ball of frozen gases and other matter -- only about six
miles in diameter. As it nears the sun, the material
warms and sublimates into gas. The result is a great tail
of ionized gas -- maybe a hundred million miles in
length. As it passes about the sun, the solar wind sweeps
the tail outward, so it points away from the sun. It
doesn't stream out behind the comet as we'd expect.
In fact, as we look at comets, we sometimes view them
along the line of their tails, even though they aren't
moving toward us. When that happens we see unlikely, and
sometimes ominous, shapes -- multiple tails or question
marks in the sky.
The strange brilliance of comets has always touched us
with awe. As a teacher, I especially like the way the
great biologist Carl Linnaeus used the metaphor when he
said of his students,
... the true discoverers are among them,
as
comets among the stars.
I'm John Lienhard, at the University of Houston, where
we're interested in the way inventive minds work.
(Theme music)
Rudaux, L., and de Vaucouleurs, G., Larousse
Encyclopedia of Astronomy. London: Paul Hamlyn, 1962.
Chapter 8.
Musique des Chansons de Béranger,
Septiéme Édition, Paris: Perrotin,
Libraire-Éditeur, MDCCCLVIII, p. 207.
Kenneth W. Burchell writes from the University of Idaho to
point out that there was a Comet of 1832. It was written
about by "Oliver Wendell, Holmes, Elijah Burritt, and most
competently by Gilbert Vale in his book COMETARIUM.."
For several closeup NASA photos of Halley's Comet, see:
this Halley's Comet site.
