The comet is called C/2011 L4 PANSTARRS, and it’s a frozen ball of dirt with a long tail made of debris. PANSTARRS isn’t coming very close to our planet –the closest it gets is 170 million kilometers, more than 400 times the distance between the Earth and the Moon. But the comet’s tail is roughly ten times longer than the Earth is wide, and as it passes through our neighborhood all that ice and dust reflects light, so the comet shines bright in the night sky.
…PANSTARRS will remain in our night sky through the end of the month.
Nasa has this helpful graphic in their ScienceCasts: A Naked-Eye Comet so that you might catch a glimpse before the view grows dim.
via Wired Science.