Observational Cosmology Seminar

Launched in March 2025, the SPHEREx mission aims to survey the full sky in near-infrared (NIR) between 0.75 – 5.0um. SPHEREx operates from a low-Earth, sun-synchronous polar orbit, where NIR airglow, particularly from HeI λ10830, OI λ8446, and OI λ11287, is present in most SPHEREx observations. In this talk, I will show how the airglow emission appears in SPHEREx observations and our analytical framework to extract atmospheric emission lines in the presence of astrophysical backgrounds including stars, resolved galaxies, and the diffuse Zodiacal light. I will present the resulting global measurements using eight months of survey data, which reveal temporal variability over the survey period and systematic dependencies on geographic location. These measurements are obtained along upward looking lines of sight as part of the astrophysical survey, in contrast to conventional nadir-viewing Earth remote sensing, which probes the behavior of low-density material in the thermo- and exosphere. I will then discuss our interpretation of these variations in the context of variable Solar illumination, seasonal effects, and the SPHEREx mission survey plan. SPHEREx, an astrophysical space observatory, is demonstrated to be a promising new platform for monitoring NIR airglow and investigating its coupling to Solar activity and global geophysical processes.