SKYSURF: Preliminary ~0.2-1.7 μm Sky Surface Brightness Measurements with Hubble

Although the Hubble Space Telescope (HST) is well-known for its exquisite point source sensitivity and stability, the dim foreground and background light that makes up more than 95% of all the photons it receives remains poorly understood. This sky surface brightness (sky-SB) is a combination of Zodiacal Light, Diffuse Galactic Light, and Extragalactic Background Light (EBL), as well as stray light from the Earth, Sun, and Moon. Therefore, panchromatic sky-SB levels measured across the entire sky with HST can provide important insight into subjects ranging from solar-system objects (Zodiacal Dust/Kuiper Belt Objects) to the flux from distant galaxies (diffuse and integrated EBL). A recently approved HST Archival Legacy program — SKYSURF, the largest HST archive program to date — is measuring the ~0.2-1.7 μm sky-SB from over 220,000 HST images using its four main cameras. We describe sky-SB measurement algorithms designed for SKYSURF that are able to recover the true sky-SB levels to within 1%. In addition, these algorithms are able to identify and flag images that contain unreliable sky-SB measurements. In this work, we present our preliminary measurements of the sky-SB after running the most reliable algorithms on the entire SKYSURF database.