Comet ISON is potentially the "comet of the
century" because around the time the comet makes its closest approach to
the Sun, on November 28, it may briefly become brighter than the full Moon.
Right now the comet is far below naked-eye visibility, and so Hubble was used
to snap the view of the approaching comet, which is presently hurtling toward
the Sun at approximately 47,000 miles per hour. When the Hubble picture was
taken on April 10, the comet was slightly closer than Jupiter's orbit at a
distance of 386 million miles from the Sun. Even at that great distance the Sun
is warming the comet enough to trigger outgassing from its frozen gases locked
up in the solid nucleus.