V838 Mon is an unusual variable star located in Monoceros (07h 04m 04.80s, -03d 50' 51.0"). It was discovered in early 2002 and was initially thought to be a classical nova. Subsequent observations indicated that this nova outburst was different than that of a classical nova. There have been several theories put forth to explain this object. A possible collision of two stars, a star engulfing its giant planets or a thermonuclear event within a massive supergiant star are some of the leading theories. There have been two other similar objects observed and these types of variables are sometimes called "red novae" due to the prodigious amount of infrared light they emit following their outbursts. V838 Mon was V magnitude 15 or 16 prior to its outburst and brightened to 6.7 at its peak. This star was also notable for the light echo that was visible around the star later in 2002. HST imaged this light echo in remarkable detail from 2002 to 2006. The star faded to magnitude 15.8V by late 2002 but in recent years has slowly brightened to 14.2V.
The image above show the appearance of V838 Mon in October, 2002 in V and I filters. Note the smoke ring shaped light echo as well as the fact that V838 Mon is much brighter in the I band than V.
The light curve above from the AAVSO shows the brightness of V838 Mon from 2002-2013. Note the slow brightening trend since 2003. Click on image for a larger version.
The light curve above from the AAVSO shows the brightness of V838 Mon from 2002-2003. Note the three distinct peaks in brightness in early 2002. Click on image for a larger version.