The luminosity of the famous red supergiant VY CMa ( L \sim 4 - 5 \times 10 ^ { 5 } L _ { \odot } ) is well-determined from its spectral energy distribution and distance , and places it near the empirical upper luminosity limit for cool hypergiants .
In contrast , its surface temperature is fundamentally ill-defined .
Both contradict a recent paper by Massey , Levesque and Plez ( 2006 ) .
Implications for its location on the HR Diagram and its apparent size are discussed .