A composite figure of the Andromeda galaxy (M31) highlights the extremely large field of view of NASA's upcoming Wide Field Infrared Survey Telescope (WFIRST). The background consists of ground-based imagery of the main disk of the Andromeda galaxy from the Digitized Sky Survey (DSS). A photo of the full Moon from NASA's Lunar Reconnaissance Orbiter is provided for scale: Andromeda has a diameter of about 3 degrees on the sky, while the Moon is about 0.5 degrees across. (In reality, the Moon is much smaller than Andromeda, but it is also a lot closer.) Outlined in teal is the region of Andromeda covered by the Panchromatic Hubble Andromeda Treasury (PHAT) mosaic, the largest Hubble mosaic ever created. Overlaid on the PHAT region and outlined in white is the footprint of the 18 square detectors that make up WFIRST's Wide Field Instrument (WFI). The entire footprint covers about 1? times the area of the full Moon and represents the area captured in a single shot by WFIRST (0.28 square degrees of the sky). The PHAT, which covers a 61,000-light-year swath of Andromeda, consists of more than 400 composite images collected over more than 650 hours of infrared observing time between 2010 and 2013. WFIRST could cover the entire PHAT, at the same resolution, with just two pointings in less than half an hour.
Background image: Digitized Sky Survey and R. Gendler, Moon image: NASA, GSFC, and Arizona State University, WFIRST simulation: NASA, STScI, and B. F. Williams (University of Washington)