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Credit: J. Aasland,
Norway
Explanation:
Does a comet's dust tail always orbit behind
it? Since comets rotate, they shed gas and dust
in all directions equally. Small ice and dust
particles expelled by the comet, however, are literally pushed
around by sunlight. The smaller the particle, the greater the
effect. When the comet
is headed inward, sunlight slows down small particles so they
orbit behind the comet. When the comet is headed back out
though, sunlight speeds them up, so small particles orbit in front
of the comet. Comet Hale-Bopp
itself is too big to have its orbit affected by the momentum of
sunlight. Therefore, since Comet Hale-Bopp
started back out to the outer Solar System two days ago, we can
expect the dramatic dust tail shown above
to shift in front in the coming days. 
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NASA Web Site Statements, Warnings, and Disclaimers
NASA Official: Jay Norris. Specific rights apply.
A service of: LHEA at NASA / GSFC
& Michigan Tech. U.
Based on Astronomy Picture
Of the Day