On March 25, 2002 IAUC 7859 included the first announcement about the discovery of a light echo around V838 Mon using the USNO Flagstaff Station 1.0-m telescope. AAVSO Council Member Arne Henden (Universities Space Research Association and U.S. Naval Observatory (USNO)) along with U. Munari (Padova) and M. Schwartz (Tenagra Observatory) announced that a light echo was first detected on February 17 and had continued to grow in size as the object faded. This light echo would go on to prove one of the most interesting (and beautiful) traits of a very enigmatic star. The only previous nova light echoes were detected in 1901 and 1936.

The light echo is caused by energy from the eruption interacting with dust surrounding the star. The interaction scatters the light, making it very bright in the cooler wavelengths. In fact, at its peak V838 Mon would have been visible in the daytime sky if your eyes could see into the infrared. It is believed that the dust surrounding the star exists as slowly expanding shells shed during the star's (or a companion's) earlier life. As the energy from the outburst reaches each shell, its brightness changes based on the density and geometry of the shell and the outburst energy. Measuring the growth rate of the echo gives us an estimated distance from Earth of around 7500 light years.