Discovery of Leonid Meteoric Cloud
KOBE UNIV (JAPAN)
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A meteoric cloud is a faint glow of sunlight scattered by the small meteoroids in the trail along a parent comets orbit. Here we report the first detection of the meteoric cloud associated with the Leonid meteor stream. Our photometric observations, performed on Mauna Kea, Hawaii, reveal the cloud as a local enhancement in sky brightness during the meteor shower in 1998. The radius of the trail, deduced from the spatial extent of the cloud, is approximately 0.01 astronomical unit and is consistent with the duration of the meteor stream activities. The brightness of the cloud is approximately 2-3 percent of the background zodiacal light and cannot be explained by the simple model calculations based on the zenith hourly rate and population index of the meteor stream activities in 1998. If the typical size of the cloud particles in 10 urn and the albedo is 0.1,the brightness is transformed into a number density of 1.5e.16cm3.