V838 Monocerotis (V838 Mon) is a variable star in the constellation Monoceros about 20,000 light years (6 kpc) from the Sun. The star experienced a major outburst in early 2002. Originally believed to be a typical nova eruption, it was then realized to be something completely different. The reason for the outburst is still uncertain, but several theories have been put forward, including an eruption related to stellar death processes and a merger of a binary star or planets. In this case of V838 Monocerotis, the light echo produced was unprecedented and is well documented in images taken by the Hubble Space Telescope.