Comet ISON Preview (Video) S&T senior editor Alan MacRobert tells you what you need to know to get ready for Comet ISON. When amateur astronomers discovered Comet ISON in September 2012, its unusual brightness caused some to hail it as the “Comet of the Century,” on a perilous course to graze the Sun in late 2013. However, the most recent observations indicate ISON (C/2012 S1) is on track to produce a somewhat less spectacular display, hopefully (but not definitely) reaching naked-eye visibility in the night sky in December 2013. To S&T senior editor Alan MacRobert, that doesn’t make the opportunity to see it any less meaningful. MacRobert explains just why it’s so tricky to predict how bright ISON will be, and previews what you’ll need to know to spot it as it approaches the Sun for its close encounter. Take a look: Follow MacRobert's updates on ISON. And if you're in a speculative frame of mind, tell us your prediction for how well Comet ISON will perform come December.