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Meteors
 

A meteor is an object from space that becomes glowing hot when it passes through the Earth's atmosphere. Consider a piece of rock or a clot of cosmic dust that travels through space. The Earth is exposed to a continuous bombardment by such objects of varying sizes. During their interaction with the Earth's atmosphere, the objects' temperature increases drastically. As a result, small celestial bodies that enter the Earth's atmosphere usually burn up or evaporate before they reach the Earth's surface, leaving behind a bright trace of light. The velocity of small celestial bodies entering the Earth's atmosphere usually ranges from 11 to 75 km/s.

The rate of appearance of meteors in proximity to the Earth and their celestial distribution are not always uniform. Star showers are frequently observed in approximately the same regions of the sky during at a given period of time (usually, for several consecutive nights). If we trace these occurrences, they will converge at a single point known as the star shower radiant. Many star showers are periodical, occurring only once each year. Their names are associated with constellations where their radiants lie. Thus, an annual star shower that is observed approximately from July 20 to August 20 is called Perseids because its radiant is in Perseus constellation. Star showers Lyrids (mid-April) and Leonids (mid-November) were named after Lyra and Leo constellations, respectively.

The intensity of star showers differs from year to year. There are years when the number of meteors in a shower is very small, while relatively strong star showers occur in different years. The years of intensive meteor showers repeat in a certain pattern. Variable activity of star showers is explained by uneven distribution of meteors along the elliptic orbit of their travel through space, which crosses the Earth's orbit. On average, about 50 meteors per hour may be seen during a star shower.

If the orbit of a comet crosses the Earth's orbit, star showers are annually observed when the Earth arrives at the point of intersection. Showers increase in magnitude if the Earth and a comet's remnants approach a given point simultaneously. If no increase magnitude is observed, it is assumed that the comet's substance has been scattered along the orbit more or less evenly, and the comet itself completely ceased to exist as a celestial body.

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