The temperature structure of the outer disk of HD 100546. Overplotted are the radial τ = 1 surface in the optical (solid thick line) as well the vertical τ = 1 surfaces of the continuum at 24, 33 and 69 μm (dotted, dashed, dot-dashed). Note that the vertical τ = 1 surface is calculated from above, meaning that regions with higher optical depth lie below it. The 69 μm surface lies below the disk midplane, meaning that the disk is close to getting optically thin at these wavelengths.