In late September, astronomers using a telescope in Russia spotted a new comet, now going by the name of C/2012 S1 (ISON). It's currently not visible without some fairly high-end hardware, but the preliminary calculations of its trajectory suggest that it's likely to pass close to both the Earth and Sun about a year from now, a path that has the potential to provide a once-in-a-lifetime show. According to a number of articles that appeared at about the same time, the comet's orbit is taking it nearly directly at the Sun, and will get within 1.4 million kilometers of the Sun's surface in November of next year, which should provide a lot of heat to melt the surface and expel gas from the comet. By January, it will be about 60 million kilometers from Earth.
That combination could, according to some estimates, leave the comet looking brighter than the full Moon, and could make it the brightest comet on record. But the actual brightness will depend heavily on details like the comet's composition and how much of its material gets ejected once it heats up. There have been some hotly anticipated comets that didn't live up to expectations, and a few that have turned out to be pleasant surprises. But if ISON is anywhere close to some of the higher estimates, we'll be in for quite a show.
Recently spotted comet may provide once-in-a-lifetime show | Ars Technica