Astronomical Sky Quality Near Eureka, in the Canadian High Arctic

Nighttime visible-light sky brightness and transparency are reported for the Polar Environment Research Laboratory (PEARL), located on a 610 m high ridge near the Eureka research station at 80° latitude, on Ellesmere Island, Canada. Photometry of Polaris obtained in the V band with the PEARL All Sky Imager (PASI) over two winters is supported by standard meteorological measurements and visual estimates of sky conditions from sea level. These data show that during the period of the study, 2008/2009 and 2009/2010 October through March, the sky near zenith had a mean surface brightness of 19.7 mag arcsec^-2 when the Sun was more than 12° below the horizon, reaching 20.7 mag arcsec^-2 during astronomical darkness with no Moon. Skies were without thick cloud and potentially usable for astronomy 86% of the time (extinction < 2 mag). Up to 68% of the time was spectroscopic (≤ 0.5 mag), attenuated by ice crystals, or clear with stable atmospheric transparency. Those conditions can persist for over 100 hr at a time. Further analysis suggests the sky was entirely free of ice crystals (truly photometric) 48 ± 3% of the time at PEARL in winter and that a higher elevation location nearby may be better.