2.4 Forming of meteor currents
By fragmentation of comet nucleus it is possible to explain the shaping not only of the cometary’s tails but also of the meteor currents.
As before mentioned, in 1866 the comet Biela completely disintegrated and arouse a cloud of meteorites that seemed originating from the constellation Andromeda. E. Weis calculated that the Earth will pass in close proximity to the orbit of the late comet on November 1872. Indeed on November 27, 1872, fragments of the comet Biela appeared like a swarm of falling stars of an extension and intensity rarely seen from the Earth. At Moncaliery (Italy), four observers counted up to 33400 falling stars in six hours and a half; at Göttingen (Germany) 7651 falling stars were counted in less than three hours.
Later on, other relations were established among nuclei of certain comets and meteor currents. Lyrids (from the constellation Lyra) were associated to the comet 1861 I. Leonids (from the constellation Leo) were associated to the comet 1866 I.
The comet Halley has already produced two swarms: Eta Aquarids, between April 30 and May 11, appearing in May, and Orionids, in October 15-26.
D. Kirkwood was the first to formulate (in 1861) the hypothesis of the cometary’s origin of the meteorites. Later on G. Schiapparely (1871) and L. Picart (1892) enunciated that the spreading of fragments and particles resulted from the nucleus of a comet along the orbit of this comet is possible only by the Sun’s differentiated pull applied to the swarm of fragments and particles. Of course, this is the solution of the problem, but it is contradictory to the present theories of gravitation, which do not admit the dispersion of the cometary’s cloud. According to the Newtonian theory and even to the general relativity, the particles resulting from the comet fragmentation should rotate on the same orbit as of the comet itself.
The distribution of the particles of a meteor current along the mother orbit is not uniform; here and there appear some accumulation of particles. This explains "the rains of falling stars", more or less intense, when the Earth crosses the orbit of a current. The distribution of the particles on the initial orbit gets so much more uniform as the current seems older, and on this basis it is possible to calculate the "age" of the current. The lack of uniformity of the meteor’s current it explained in vortex theory by two mechanisms:
- different acceleration of particle separated form comet’s nucleus;
- modification of parameters of comet’s orbit after a revolution in case of periodic comets
As to the breadth of the meteor currents, it is proportional to the duration of activity of the respective radiant. Thus the radiant activity of the Perseids (current proceeding from the comet 1892 II) was observed by Hoffmeister from July 20 to August 19, 1948. Thereby was obtained the conclusion that the breadth of this current was of 0,5a.u., approximately 75,000,000 km. The distribution of the particles along the current was almost uniform. According to E. Ahmert-Rohlfs, the age of this current may be of 80,000 years.
By the hourly frequency of the meteors it is also possible to evaluate the spatial density of the current, precisely the mean distance among its particles. There are very dense currents (Leonid, observed in 1833), where the measured mean distances among particles are of 15-30 km, and there are currents where distances are of 1,000 to 2,000 km, and more. Of course, in the evolution of the meteor fragments, under the action of the differentiated motion, there is a moment when the width of the meteor current is so large that the current itself loses its individuality and diffuses throughout the fluid environment.