SKYSURF-4: Panchromatic Hubble Space Telescope All-Sky Surface-brightness Measurement Methods and Results

The diffuse, unresolved sky provides most of the photons that Hubble Space Telescope (HST) receives, yet remains poorly understood. HST Archival Legacy program SKYSURF aims to measure 0.2-1.6 $\mu$m surface brightness (sky-SB) from over 140,000 images. We describe a sky-SB measurement algorithm designed for is able recover input simulated images within 1% uncertainty. present our measurements estimated using this on entire database. Comparing spectral energy distribution (SED) literature shows general agreements. Our SED also reveals possible dependence Sun angle, indicating either non-isotropic scattering solar off interplanetary dust or an additional component Zodiacal Light. Finally, we update Diffuse Light limits in near-IR based methods Carleton et al. (2022), with values 0.009 MJy sr$^{-1}$ (22 nW m$^{-2}$ sr$^{-1}$) at 1.25 $\mu$m, 0.015 (32 1.4 and 0.013 (25 1.6 $\mu$m. These estimates provide stringent all-sky constraints date wavelength range. are made public official website will be used constrain future papers.