Solar Elongation Dependence of Zodiacal Light Surface Brightness

This paper examines How rapidly zodiacal brightness rises toward the Sun, quantified as a gradient law in elongation. Using only published input values and transparent formulae, the calculation obtains the following headline results: brightness_S10_at_90deg = 90; brightness_S10_at_60deg_model = 107; brightness_S10_at_30deg_model = 206.8; ratio_30deg_to_90deg = 2.3; adopted_gradient_exponent = 1.2; brightness_S10_at_120deg_model = 107. Brightness at thirty degrees elongation exceeds that at ninety degrees by a factor of about 2.3 in the fitted law, a gradient that foreground models for wide-field surveys must reproduce. The method, inputs and limitations are stated in full so that any reader can reproduce or rescale every number from the deposited calculation script. Agreement and disagreement with independent published estimates are reported at their actual size, and the conclusions are limited to what the budget arithmetic supports.