SOUTHWEST, Stock Photographs

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This Week's Photograph - 1 December 2013<br />
Comet Ison, the Comet of the Century may be a bust, but here is Hale-Bopp for consolation.<br />
Comet Hale-Bopp races through the desert sky above a saguaro cactus silhouette near Tucson, Az on March 19, 1997.<br />
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Comets are mysterious and inspire awe. They were looked upon as foreboding heavenly messengers, harbingers of doom, foretelling disasters and misfortune. That is until the scientific revolution proved a more sound explanation. A comet's nucleus is composed of ice and dust. As it nears the Sun during its orbit, some of the ice evaporates as its surface is heated. This gas becomes ionized and is drawn outwards by the solar wind to form a tail which points away from the Sun. The released dust may also form a second tail as it is pushed by radiation pressure.<br />
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Hale-Bopp Facts: Hale-Bopp is as old as our sun, 4.5 billion years and takes 2,392 Earth years to complete its orbit. It could be seen for 19 months, from May 1996 to November 1997. It was discovered by Alan Hale and Thomas Bopp on July 23, 1995