Star V838 Mon's light echo seen from the Hubble Space Telescope

Star V838 Monocerotis's (V838 Mon) light echo, which is about six light years in diameter, is seen from the Hubble Space Telescope in this February 2004 handout photo released by NASA on December 4, 2011. Light from the flash is reflected by successively more distant rings in the ambient interstellar dust that already surrounded the star. V838 Mon lies about 20,000 light years away toward the constellation of Monoceros the unicorn. It became the brightest star in the Milky Way Galaxy in January 2002 when its outer surface greatly expanded suddenly.