Methods

The background due to the Solar System and the Galaxy at Spitzer is dominated by two sources: the zodiacal light and interstellar cirrus. At shorter wavelengths, and at low galactic latitudes, starlight is a potential contribution. For the present model, I will neglect starlight, because Spitzer will resolve and detect the vast majority of stars. I estimate the integrated light of undetectable stars to be less than 0.05 $\mu$Jy/pixel at $b=30^\circ$, so that starlight is negligible compared to zodiacal light except at latitudes $\vert b\vert<0.2^\circ$at $l>30^\circ$ (based on results presented by Leinert et al. 1998). It is unlikely that we could provide an accurate model of the inner galactic plane in any event; galactic plane observers will have to inspect their own ground-based observations or the MSX and 2MASS maps, which are beyond the present scope because they aren't available yet.