Comet Pan-STARRS is seen over the western horizon and just above Mount Taylor, from Albuquerque, N.M., Tuesday evening, March 12, 2013. The comet passed within 100 million miles of Earth last week. (AP Photo/Albuquerque Journal, Morgan Petroski)
Photo: Associated Press

Comet Pan-STARRS is seen over the tower on the left as a one-day day waxing crescent moon is seen setting in the western sky on Tuesday, March 12, 2013. The dark side of the moon is lit by reflected light from the Earth, and is called Earthshine. (AP Photo/Dr. Scott M. Lieberman) Photo: Ap/getty

TOPSHOTS Comet PanSTARRS (L) is seen with a one-day old crescent moon as both set over the Very Large Array radio telescope antenna dishes Tuesday, March 12, 2013, near Magdalena, N.M. The comet, now just faintly visible in the northern hemisphere, was discovered in June 2011 by the Panoramic Survey Telescope and Rapid Response System (PanSTARRS) in Hawaii. (STAN HONDA/AFP/Getty Images) Photo: Ap/getty

Comet Pan-STARRS is seen about 40 minutes after Sunset in the Western sky from Tyler, Texas on Tuesday, March 12, 2013. Photo: A

Comet PanSTARRS sets over the Very Large Array radio telescope antenna dishes Tuesday, March 12, 2013 near Magdalena, N.M. The comet, now just faintly visible in the northern hemisphere, was discovered in June 2011 by the Panoramic Survey Telescope and Rapid Response System (PanSTARRS) in Hawaii. ( STAN HONDA/AFP/Getty Images) Photo: Ap/getty

 The comet PanSTARRS, above and to the left, passes over the Stratosphere Casino Hotel along with a waxing crescent moon at twilight over the Spring Mountains range on Tuesday,  March 12, 2013, in Las Vegas, Nev.  (Photo by Ethan Miller/Getty Images) Photo: Ethan Miller, Ap/getty

 The comet PanSTARRS, above and to the right, passes over the Stratosphere Casino Hotel along with a waxing crescent moon over the Spring Mountains range on Tuesday, March 12, 2013, in Las Vegas, Nev. (Photo by Ethan Miller/Getty Images) Photo: Ethan Miller, Ap/getty

The comet PanSTARRS passes over the Stratosphere Casino Hotel on Tuesday, March 12, 2013 in Las Vegas, Nev. (Photo by Ethan Miller/Getty Images) Photo: Ethan Miller, Ap/getty

Comet PanSTARRS (L) is seen with a one-day old crescent moon as both set over the Very Large Array radio telescope antenna dishes March 12, 2013 near Magdalena, New Mexico. The comet, now just faintly visible in the northern hemisphere, was discovered in June 2011 by the Panoramic Survey Telescope and Rapid Response System (PanSTARRS) in Hawaii. AFP PHOTO/Stan HONDA (Photo credit should read STAN HONDA/AFP/Getty Images) Photo: Ap/getty

In this Sunday, March 10, 2013 photo taken with a 600-millimeter telephoto lens, comet Pan-STARRS appears between the clouds low in the western sky as seen from Harrells, N.C. The comet, which was closest to the sun on Sunday, is expected to become more easily visible to observers in the Northern Hemisphere this week. (AP Photo/The Fayetteville Observer, Johnny Horne) Photo: Ap/getty

The comet Pan-STARRS, left, is visible next to a crescent moon in the western sky after sunset over Westminster, Md. Tuesday, March 12, 2013. The comet's name is actually an acronym for the telescope in Hawaii used to discover it two years ago: the Panoramic Survey Telescope and Rapid Response System. It will be visible in the Northern Hemisphere for weeks to come. (AP Photo/The Carroll County Times, Dylan Slagle) Photo: Ap/getty

Comet PanSTARRS (left) appears to the left of a slim crescent moon in Tuesday March 12, 2013 evening's western sky. The comet rounded the sun on Sunday and is now visible low in the western evening sky. This picture was made shortly after sunset near Harrells, NC. (AP Photo/The Fayetteville Obsever- Johnny Horne) Photo: Ap/getty

Comet Pan-STARRS is seen about 40 minutes after sunset in the western sky from Tyler, Texas, on Tuesday, March 12, 2013. (AP Photo/Dr. Scott M. Lieberman) Photo: Ap/getty

This image provided by NASA shoaws the comet PANSTARRS as seen from Mount Dale, Western Australia on March 5, 2013.  (AP Photo/NASA) Photo: Ap/getty

This March 2, 2013 photo made available by spaceweather.com shows the comet, Pan-STARRS, seen from Queenstown, New Zealand. (AP Photo/spaceweather.com, Minoru Yoneto) Photo: Ap/getty