In this Hubble Space Telescope composite image taken in April 2013, the sun-approaching Comet ISON floats against a seemingly infinite backdrop of numerous galaxies and a handful of foreground stars.

The icy visitor, with its long gossamer tail, appears to be swimming like a tadpole through a deep pond of celestial wonders.

In reality, the comet is much, much closer. The nearest star to the Sun is over 60,000 times farther away, and the nearest large galaxy to the Milky Way is over thirty billion times more distant.

These vast dimensions are lost in this deep space Hubble exposure that visually combines our view of the universe from the very nearby to the extraordinarily far away.

CLICK FOR LARGER IMAGE. This photo is one of the original images featured on ISONblog, a new online source offering unique analysis of Comet ISON by Hubble Space Telescope astronomers and staff at the Space Telescope Science Institute in Baltimore, Md.

"Is ISON unique?" asked Mike A'Hearn at the meeting of comet observers and scientists at the Johns Hopkins University Applied Physics Laboratory.

The answer: sungrazing comets are commmon. Fresh-from-the-Oort-cloud comets are common. Comets detected more than 6 times farther out than the Earth's orbit? Not so much. The combination of all three is very rare.

Also, read the fascinating Finding ISON by Josh Sokol.