Glossary - Astronomy Magazine

Comet C/2011 L4 (PANSTARRS)

Comet C/2012 S1 (ISON)

Glossary

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zenith the point on the celestial sphere directly over the head of an observer
zenithal hourly rate the number of meteorites expected to be seen per hour when a meteor shower's radiant is at an observer's zenith; abbreviated ZHR
zodiac a band around the celestial sphere 18° in width and centered on the ecliptic
zodiacal light a faint, cone-shaped glow of light seen in the west after nightfall or in the east before dawn, caused by sunlight reflecting and scattering off interplanetary dust particles lying along the ecliptic plane

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