“Once in a Civilization” Comet to Zip past Earth Next Year | Observations, Scientific American Blog Network: “After it loops around the Sun and forms this tail, the comet should then pass relatively close to Earth—not near enough to cause any worry, but close enough to put on a great show. Viewers in the Northern Hemisphere will get the best view as the comet blooms in the weeks approaching Christmas 2013. The comet could grow as bright as the full moon.“
Comet brightness predictions sometimes exceed their performance. Amateur astronomers of a certain age may remember the Comet Kohoutek hype of 1973 – not quite the ‘damp squib’ it has been portrayed, since it reached naked eye visibility! Even if C/2012 S1 takes on the same light curve as Kohoutek it is certain to be spectacular, quite possibly a once-in-a-civilisation’s-lifetime event.