COMETS
Reading edition
During the past century, many of these “tramps of the solar system” have been discovered and their orbits computed. The “head” may range from ten thousand to a million miles, or more, while its “tail” may stream across the heavens for millions of miles. These comets’ tails always point away from the sun; and for long the reason for this was not known. It is now believed that this is due to light-pressure; the energy of the sun’s rays press this delicate matter outwards into space. (This theory has been elaborated at considerable length by the Swedish astronomer and chemist, Arrhenius.)
Many readers of this little book will remember the excitement caused by Halley’s comet, which came relatively close to the earth in 1910, so that many persons thought there would be a collision, and were terrified accordingly! As a matter of fact, the tails of comets are usually of almost inconceivable tenuosity. Halley first observed this comet, computed its orbit and predicted the date of its return.
Some comets have tails: others do not. Not much is known concerning the origin and destination of comets; where they originated, or how. They travel at tremendous speed over many millions of miles of space, returning after a few years, or after a lapse of several centuries. They are very striking looking, even when observed by the naked eye. A number of comets have been noted. The following are a few of the more remarkable comets which were observed during the past century:
The Comet of 1811. This was visible for nearly a year and a half, and was carefully studied by William Herschel. Its tail was said to be nearly a hundred million miles long, and fifteen million miles broad.
Encke’s Comet (1819). This comet is of extreme interest because of its change of volume. Moulton says: “On October 28, 1828, it was 135,000,000 miles from the sun, and had a diameter of 312,000 miles. On December 24, its distance was 50,000,000 miles and its diameter was 14,000 miles; while at its perihelion passage of December 17, 1838, at a distance of 32,000,000 miles, its diameter was only 3,000 miles.”
Beila’s Comet (1826). This comet has a most interesting history. In 1846 it was again seen; and a month later it had divided into two parts. They traveled along parallel orbits, some 160,000 miles apart. In 1852, they were seen to be 1,500,000 miles apart. Since then they have never been seen. They have, apparently, vanished from the face of creation!
Donati’s Comet (1858). This comet was visible for more than nine months. Its tail was estimated as 54,000,000 miles long. Its period of revolution was more than 2,000 years.
The Great Comets of 1880 and 1882. The latter of these passed through some hundreds of thousands of miles of the sun’s corona. Its orbit was not appreciably changed, but, after emerging, it was seen to possess at least five nuclei—showing the effect upon the comet of the disruptive forces through which it had passed.