A Robotic Wide‐Angle Hα Survey of the Southern Sky

We have completed a robotic wide‐angle imaging survey of the southern sky (δ = +15° to −90°) at 656.3 nm wavelength, the Hα emission line of hydrogen. Each image of the resulting Southern Hα Sky Survey Atlas (SHASSA) covers an area of the sky 13° square at an angular resolution of approximately 0 8 and reaches a sensitivity level of 2 R (1.2 × 10 -17 ergs cm −2 s −1 arcsec −2 ) pixel −1 , corresponding to an emission measure of 4 cm −6 pc and to a brightness temperature for microwave free‐free emission of 12 μK at 30 GHz. Smoothing over several pixels allows features as faint as 0.5 R to be detected.