Comet 17P/Holmes was the second surprise comet of 2007. The first was Comet 2006/P1 (McNaught), which brightened rapidly and spectacularly in early January 2007. By midmonth, Comet McNaught had achieved magnitude –5.5 and was visible in broad daylight for several days. Southern Hemisphere observers then got to see the brightest comet in 40 years sporting a 35°-long tail that fanned across the evening sky.
Stephen James O’Meara’s secret sky: Remembering 2007’s comet double feature
May 2008: Although Comet Holmes did not rival Comet McNaught in brightness or develop a spectacular tail, it did flare nearly half a million times in brightness.