= Thermal eclipse depth
For <blackbody> star and planet, define the planet-star contrast
$$
r_\lambda=\frac{F_{p,\lambda}}{F_{*,\lambda}}=\left(\frac{R_p}{R_*}\right)^2\frac{B_\lambda(T_p)}{B_\lambda(T_*)}.
$$
A complete <exoplanet secondary eclipse> removes the planet's light from the combined out-of-eclipse light. Its exact normalized depth is $d_\lambda=r_\lambda/(1+r_\lambda)$. The common approximation $d_\lambda\simeq r_\lambda$ requires $r_\lambda\ll1$. This thermal model omits reflected light and spatial variations.
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