Comets

celestial bodies that come from space, pass around the sun and disappear in space again. They are accompanied by trails of light, hence the name which is derived from a Greek word meaning hair. Over eight hundred comets have been studied and listed. Some return with regularity. Others are not expected again. Encke's comet was rediscovered September 12, 1904, at a distance of 107,000,000 miles from the earth. It swept around the sun at the rate of 1,250,000 miles a day, and disappeared in space. Some comets are visible for a week or two, others for months. One has been seen for two years. Some are bright enough to be seen in the day-time; others are visible only at night and by means of a telescope.

Tycho Brahe discovered that comets are celestial bodies outside of our atmosphere. Newton demonstrated that the force which keeps the planets in their orbits controls also the comets. Halley first proved that comets return at regular intervals, or have, as astronomers say, periodicity. Of these, Halley's comet has a period of about 75 years; Encke's 1,204 days; that of Biela, 6 3/4 years; that of Faye, 7 1/2 years.

Planets move from west to east; but comets move from east to west. The orbits or paths of planets are elliptical; those of comets take various forms of ellipses or parabolas, usually the latter.

A comet consists of a head, containing usually a more or less condensed portion called a nucleus, and a luminous wisp which always points away from the sun. When approaching the sun, the train streams out behind like hair. When the comet is receding the same imposing light streams out in advance, suggesting a swarm of luminous star dust, repelled by electricity in a direction opposite to that of the sun. The tail is seldom less than 5,000,000 miles long, and in some comets attains a length of 100,000,000 miles.

Comets have been regarded as dread portents of war and pestilence and famine. Milton speaks of a live comet that

Shakespeare says:

Astronomers also have felt what now seems needless alarm lest one of these brilliant travelers should collide with the earth. It now appears that no more harm is to be apprehended from the tail of a comet than from the northern lights, while the chance of running into a nucleus is remote, and is unlikely to be attended with serious result. Very possibly a shower of shooting stars would be the only noticeable phenomenon. The density of a comet does not exceed that of the residuum of air left in a first class air pump.

Professor Young answers the question of how it is possible for so light a body to make headway in space, by saying that space is a perfect vacuum offering no resistance to the passage of bodies. He adds the striking statement that if the earth were annihilated save a single feather, that feather would continue to move in the earth's present orbit at a rate of eighteen and one half miles a second.

See Meteor; Star