Comet C/2011 L4 (PANSTARRS) has brightened dramatically over the past week and is now visible with the naked eye from the Southern Hemisphere. Pan-STARRS is moving north rapidly and will become visible across Europe, North America and Asia from Thursday 7 March onward. The comet is expected to reach its peak brightness around the time of its closest approach to the Sun (called the perihelion) on Sunday 10 March. It may or may not lose brightness quickly afterwards, so you want to catch this comet as soon as possible!
I plotted the visibility of Pan-STARRS in the video below. Green/yellow areas in the animation indicate parts of the world where the comet will be above the horizon (and the Sun at least six degrees below the horizon). The movie shows that Pan-STARRS is only visible shortly after sunset, when it is located low above the Western horizon.