Connection between Meteors and Comets.
305. Shooting-Stars.—On watching the heavens any clear night, we frequently see an appearance as of a star shooting rapidly through a short space in the sky, and then suddenly disappearing. Three or four such shooting-stars may, on the average, be observed in the course of an hour. They are usually seen only a second or two; but they sometimes move slowly, and are visible much longer. These stars begin to be visible at an average height of about seventy-five miles, and they disappear at an average height of about fifty miles. They are occasionally seen as high as a hundred and fifty miles, and continue to be visible till within thirty miles of the earth. Their visible paths vary from ten to a hundred miles in length, though they are occasionally two hundred or three hundred miles long. Their average velocity, relatively to the earth's surface, varies from ten to forty-five miles a second.
The average number of shooting-stars visible to the naked eye at any one place is estimated at about a thousand an hour; and the average number large enough to be visible to the naked eye, that traverse the atmosphere daily, is estimated at over eight millions. The number of telescopic shooting-stars would of course be much greater.
Occasionally, shooting-stars leave behind them a trail of light which lasts for several seconds. These trails are sometimes straight, as shown in Fig. 344, and sometimes curved, as in Figs. 345 and 346. They often disappear like trails of smoke, as shown in Fig. 347.
Fig. 344.
Fig. 345.
Fig. 346.