Our Own Galaxy's Scattered Light: A Cirrus-Traced Budget for Diffuse Galactic Contamination of the Background

This paper addresses a specific question in the accounting of the cosmic optical and infrared backgrounds: how large is the diffuse Galactic light in typical high-latitude background fields, and how clean must a field be for its residual contamination to fall below one nanowatt? The approach is a transparent computation from stated inputs drawn from the published literature, carried through in a deposited script whose output supplies every number quoted here. The principal computed values are: DGL at 1MJy nW = 4; DGL at 2MJy nW = 8; residual at 1MJy nW = 0.8; residual frac of ebl at 1MJy = 0.08; I100 max for residual below 1nW = 1.25. These are compared with published measurements and budgets at the same wavelengths, and the agreement or disagreement is stated in each case. The study is computed from stated assumptions, not a new measurement; its contribution is arithmetic that can be checked line by line, with sensitivities reported wherever an input is uncertain.