Comet Holmes, 17P/Holmes, during it's remarkable 2007 outburst.
10 November, 2007. CAO, Thornbury, ON, Canada. This periodic comet, discovered by Edwin Holmes in 1892 with an orbital period of 6.8 yrs, underwent a highly unusual outburst of activity during its' 2007 return. The outburst caused the comet to brighten 500,000X and swell briefly to the largest object in the solar system (slightly larger than our Sun). This is the largest such outburst known. This image is a stack of 10x60 sec exposures with a 127mm refractor, and the images were stacked using the comet head as the registration point. Thus, the comet is in sharp focus and the stars appear as small streaks due to the motion of the comet.