1 2 2 3 3 4 5 1 2 3 4 5 ρ t ρ ∼ 0.537 ρ ∼ 0.5 ρ t ρ ∼ 0.5 ρ ∼ 0.5 1 Introduction: The outburst of V838 Mon and its ”echo” The unusual eruption activity of V838 Mon after its discovery in early January 2002 (Brown N. J. [2002]) was a subject of numerous papers and communications during the last two years (e.g., see Munari U. et al. [2002], Banerjee D.P.K. et al. [2002], Goranskij V.P. et al. [2002], Wisniewski J.P. et al. [2003] and the references there). Briefly speaking, this 16-mag star underwent at least 3 outbursts, the second of which, reaching maximum of V ≈ 6.5 on Feb. 6, 2002, was the biggest and the ”sharpest” one. A circular light echo around the central object was observed during a dozen days after this maximum Henden A. et al. [2002]. Considered to be Nova or Nova-like, V838 Mon has demonstrated a peculiar behavior and has converted into an extremely red cool object. Besides the unusual spectral evolution, the light echo´ s rapid development is what poses additional puzzles. The astrophysical echo is an extremely rare event — only 2 ÷ 3 ”Nova” — and 5 ÷ 6 ”Supernova”–echoes are known. It is rather a tool for studying the circumstellar and interstellar matter, but it can provide a reasonable estimate for the distance in certain cases. The crucial estimate when studying the event V838 Mon is the evaluation of the distance d to the object because the final Bulgarian Astronomical Journal 9, 2007