Towards a data-driven model of the sky from low Earth orbit as observed by the Hubble Space Telescope

Abstract

The sky observed by space telescopes in Low Earth Orbit (LEO) can be dominated by stray light from multiple sources including the Earth, Sun and Moon. This stray light presents a significant challenge to missions that aim to make a secure measurement of the Extragalactic Background Light (EBL). In this work we quantify the impact of stray light on sky observations made by the Hubble Space Telescope (HST) Advanced Camera for Surveys. By selecting on orbital parameters we successfully isolate images with sky that contain minimal and high levels of Earthshine. In addition, we find weather observations from CERES satellites correlates with the observed HST sky surface brightness indicating the value of incorporating such data to characterise the sky. Finally we present a machine learning model of the sky trained on the data used in this work to predict the total observed sky surface brightness. We demonstrate that our initial model is able to predict the total sky brightness under a range of conditions to within 3.9% of the true measured sky. Moreover, we find that the model matches the stray light-free observations better than current physical Zodiacal light models.

Modeling the Extragalactic Background Light and the Cosmic Star Formation History

“…The night sky is dominated by emission from the atmosphere, the solar system (zodiacal light emitted by interplanetary dust mostly within the orbit of Jupiter; e.g., Wright 2001;Rowan-Robinson & May 2013;Korngut et al 2022), and the Milky Way (e.g., Seon et al 2011;Brandt & Draine 2012;Chellew et al 2022), all of which are brighter than the EBL. Telescopes above the atmosphere can measure the EBL without the contaminating atmospheric foreground (e.g., Hauser et al 1998;Bernstein et al 2002;Mattila 2003;Bernstein 2007), although these can still suffer from contamination from stray light from the Eath, Moon, or Sun outside the field of view of the instrument (Caddy et al 2022). Spacecraft beyond the orbit of Jupiter have made measurements of the EBL with minimal contamination from the zodiacal light (Toller 1983;Edelstein et al 2000;Matsuoka et al 2011;Zemcov et al 2017;Lauer et al 2021Lauer et al , 2022.…”