You gotta love comets. OK, except when they fizzle. But outside of that, they can be tremendous fun to watch. That's so true of Comet PanSTARRS (C/2017 S3), which is now undergoing a second outburst just two weeks after its first. This latest explosion has pumped enough life into the vagabond to see it in a pair of binoculars. No kidding. I spotted with ease in my 10×50s on July 16.20 UT. Nothing fancy, just a small blob, but at magnitude ~8.2 it was obvious.
With a Frankensteinian jolt, C/2017 S3 first came to life on or about June 30th, sitting straight up at magnitude 9.5 after a three magnitude outburst. The explosion released a significant amount of C2 or diatomic carbon gas, which gives comet comas their characteristic aqua-green hue. Swan Band filters capitalize on this fact by transmitting only a few narrow slivers of light, including C2emissions, to provide clearer and contrastier views of "gassy" comets.
Days later, C/2017 S3's cor...