Let’s lay our cards on the table at the outset: No one really knows how bright Comet ISON (C/2012 S1) will get. Lots of people think they know how this comet will perform as it plunges toward the Sun this month. Optimists tout numbers that have many amateur astronomers giddy with excitement. If they’re right, the comet could rival the Full Moon when it passes closest to the Sun at perihelion November 28 and remain as bright as the planet Jupiter for several days around then.
NASA/ESA/The Hubble Heritage Team (STScI/AURA)