It has long been observed that the nuclei of periodic comets are depleted, with every turn they glow weaker. Not once was there a division of cometary nuclei into two parts or more. This destruction produced or solar tides, or collisions with a meteor shower. The comet, discovered by the Czech scientists Bilim (Biloy) in 1772 was observed with repeated returns with the seven-year period. In 1846 its core collapsed, and it turned into two weak comets, which after 1852 was not observed. When in 1872, according to the calculations, the missing comet should pass near the Earth, there was rain of “falling stars”. Since November 27 this phenomenon is repeated every year, though less effectively. Small solid particles of the disintegrated nucleus of a former comet Bilogo stretched along its orbit, and when the Earth crosses the stream, they fly in the atmosphere and evaporate. A number of other meteor showers.
Meteoroids — the remains of comets, visible only at the time of evaporation are called meteors. The width of meteor showers is much greater than the size of the generated nuclei.
Photographing the path of the same meteor in the starry sky, as he is projected to observers, separated from each other by 20-30 km, determine the altitude at which the meteor appeared. Most meteoroids begin to glow at heights of 100 to 120 km and has already completely evaporated at a height of 80 km . Visible in their spectra bright lines of iron, calcium, silicon, etc. Photographing the flight of a meteor camera, objectivation is covered by the rotating shutter, get intermittent trace showing the inhibition of meteor air. Hence determine the density of the meteoroids. She is only about 0.1 g/cm3. Probably meteoroids is porous particles, the pores of which are filled with comet ice, which vaporizes the first. According to calculations, the mass of meteoroids is of the order of milligrams, and the size — fractions of a millimeter.
The hot gases leave the meteor body, form a luminous trail, which is also ionized the air. This provided the opportunity to apply for the study of meteors radar. Unable to determine the speed of meteors. Meteoroids, catching up with Earth, are the speed with which they fly in the atmosphere, no more than 11 km/sec, and flying towards Earth with the speed of about 60-70 km/h.
Meteors sometimes seem to be departing from any of the constellations, from the sky, called the radiant of a meteor shower. This is a perspective effect. The path of meteors flying on parallel tracks being pursued, seem to be converging, as the rails of the railway. The radiant is in the sky in the direction from which flying meteoroids. Radiant has a definite position among the constellations and participates in the daily rotation of the sky. Astronomy, indicating the days when meteor showers occur with the Earth, reduces the risk of meetings with them and allows to take them into account when scheduling space flights. Meteors flying 10-12 August from the constellation Perseus, the Perseids are called.