
Comet 17P/Holmes is in outburst! Two days ago this periodic comet some 2.4 AU away from the Sun and 1.6 AU from Earth, brightened unexpectedly by a MILLION fold from 16th magnitude to nearly 2.5! You can read more about it here.
The above image was obtained through the University of Arizona's Steward Observatory 2.3 meter telescope atop Kitt Peak. The large round outer coma is about 2 arcminutes in diameter as viewed from Earth - or nearly 87,000 miles across - the size of the planet Jupiter! Given that this shell of dust was generated two days ago (~50 hours) that works out to be a expansion rate of almost 870 miles per hour! Quite a bang!
Credit: University of Arizona - Paul Smith, Dennis Means, Dave Harvey.