A robotic wide-angle hα survey of the southern sky

We have completed a robotic wide-angle imaging survey of the southern sky (delta = +15 degrees to -90 degrees) at 656.3 nm wavelength, the H alpha emission line of hydrogen. Each image of the resulting Southern H alpha Sky Survey Atlas (SHASSA) covers an area of the sky 13 degrees square at an angular resolution of approximately 0.'8 and reaches a sensitivity level of 2 R (1.2 x 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 muK at 30 GHz. Smoothing over several pixels allows features as faint as 0.5 R to be detected.