By Amanda Barnett, CNN
A rare treat for sky watchers is hovering overhead.
Comet Pan-STARRS is now visible on the western horizon in the Northern Hemisphere and viewers in the United States may be able to see it with the naked eye.
The comet has been visible through telescopes in the Southern Hemisphere for a while and amateur photographers are now posting sightings online from the Northern Hemisphere.
Scientists estimate that naked-eye comets happen only once every five to 10 years, according to the Jet Propulsion Laboratory.
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