On January 6, 2002, an unknown star flared up in Monoceros, the Unicorn. Being instantly one of the largest known red variable stars, it was designated V838 Monocerotis, about 20,000 light years from the Sun.The initial light curve resembled that of a nova, an eruption that occurs when enough hydrogen gas has accumulated on the surface of a white dwarf from its close binary companion. V838 Monocerotis reached maximum visual magnitude on February 6, 2002 after which it started to dim rapidly, as expected. However, in early March the star started to brighten again, this time mostly in infrared wavelengths. Yet another brightening in infrared occurred in early April after which the star returned to near its original brightness before the eruption, magnitude 15.6. The lightcurve produced by the eruption is unlike anything previously seen.
Rapidly brightening objects like novae and supernovae are known to produce a phenomenon known as light echo, where the light that travels directly from the object arrives first. If there are clouds of interstellar matter around the star, some light is reflected from the clouds. Because of the longer path, the reflected light arrives later producing a vision of expanding rings of light around the erupted object. In addition, the rings appear to travel faster than the speed of light.