Using a physical theory of meteors and on the basis of the results of double-station photographic observations of meteors in Dushanbe (Tajikistan), Kiev, and Odessa (Ukraine), the mean mineralogical and bulk densities of meteoroids belonging to nine meteoroid streams and sporadic background are determined. The mean mineralogical densities δ m of meteoroids range from 2.2 g cm −3 (Perseids) to 3.4 g cm −3 (Quadrantids, δ-Aquarids, and α-Capricornids). The meteoroid bulk densities δ, which were determined according to the theory of quasi-continuous fragmentation of meteoroids in the Earth's atmosphere, vary from 0.4 g cm −3 (Leonids) to 2.9 g cm −3(Geminids). Using the relation between bulk density and mineralogical density the porosity of meteoroids was estimated. The Geminid meteoroids are found to have the lowest porosity, while the Leonid and Draconid meteoroids have the most porous structure (83%). These results confirm the porous-structure nature of meteoroids' parent bodies i.e. comets and asteroids.

Abstract. The phenomenon of meteoroid fragmentation in the Earth's atmosphere was recorded repeatedly by means of different methods and especially using the photographic technique of instantaneous exposure. Among the four principal forms of fragmentation, the quasi-continuous fragmentation, i.e. a gradual release of the smallest fragments from the surface of a parent meteoroid and their subsequent evaporation, is most common. The analysis of photographic observations shows that a substantial fraction of meteoroids is exposed to this type of fragmentation. According to the theory of quasi-continuous fragmentation and on the basis of light curves of meteors photographed in Dushanbe (Tajikistan), the mean bulk densities of meteoroids belonging to six meteoroid streams and the sporadic background have been determined, which vary in the range from 0.4 g cm −3 (Leonids) to 2.9 g cm −3 (Geminids).

The dynamical evolution of meteoroid streams associated with comets Encke, Halley, Machholz 1986 VIII and asteroid Phaethon is discussed. It is shown that the planetary perturbations can greatly increase the streams thickness and each stream may produce several couples of meteor showers active in different seasons of the year. The theoretical and observed data are in a satisfactory accordance.

Abstract.Observed meteor showers associated with some Near-Earth asteroids (NEAs) is one of the few criteria that such asteroids may be considered to be candidate extinct cometary nuclei. In order to reveal new NEAmeteor shower associations, we calculated the secular variations of the orbital elements of 17 Taurid Complex asteroids with allowance for perturbations from six planets (Mercury-Saturn) over one cycle of variation of perihelia arguments. The Earth-crossing class of these NEAs and theoretical geocentric radiants and velocities of their meteor showers were determined and compared with available observational data. It turns out that each Taurid Complex asteroid is associated with four meteor showers. This is evidence for the cometary origin of these asteroids.