From SpaceWeather.com:

Astronomers report that Comet Swan has suddenly increased in brightness 4-fold, from magnitude +6 to +4.5. This makes it a naked-eye object in dark skies and a lovely sight through backyard telescopes. The cause of the outburst: A new vein of volatile ice may have opened up in the comet’s nucleus. Solar heating transforms this freshly-exposed material into streams of bright, reflective gas and dust. Indeed, backyard telescopes seem to show new tendrils of gaseous material in the comet’s long tail.

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