Comet 46P/Wirtanen will make its closest approach to the sun on December 16, and can be seen with the naked eye as it will be only 11.7 million km away from Earth and will be much brighter than it normally is. 

According to Joe Rao, FiOS 1 News meteorologist and Space.com skywatching columnist, "It will become as bright as third magnitude, which is about as bright as the faintest star in the Big Dipper. So, if you know where to look in the sky, it will be against the winter constellations of Taurus the bull, near the Pleiades and Hyades star clusters." (via Space.com)

Comet 21P/Giacobini-Zinner, or simply "21P," will make its closest approach to Earth on September 10th. A good pair of binoculars or a small telescope should be enough to see it, and be sure to look eastward after midnight to the constellation Auriga.

You can still spot the comet for several nights before and after this close approach, but how long it will stay in sight depends on how powerful your skywatching equipment is. To pinpoint Comet 21P's exact coordinates when observed from any given location or time, check out NASA's ephemeris calculator. (via Space.com)