Stargazers could enjoy a "once in a lifetime" spectacle as a bright comet swings into the Northern Hemisphere.

The icy mass, called C/2011 L4 Pan-Starrs, should be visible with binoculars or a telescope from 8 March.

But in the following days, it will become even brighter and could be seen with the naked eye.

Astronomers in the Southern Hemisphere have already been treated to a fly past, with reports that the body was as bright as stars in the Plough.

Science reporter Rebecca Morelle explained to the BBC's Stephen Sackur why the comet is particularly unusual.