Astronomical Sky Quality Near Eureka, in the Canadian High Arctic

TL;DR

This study reports on the sky brightness and transparency conditions near Eureka, Canada, demonstrating that the Arctic environment offers significant potential for astronomical observations during winter, with many clear and stable nights.

Contribution

First detailed measurement of Arctic sky brightness and transparency conditions near Eureka, providing valuable data for future Arctic astronomy site assessments.

Findings

Sky near zenith had a mean brightness of 19.7 mag/arcsec^2 during winter

Sky was clear and potentially usable for astronomy 86% of the time

Photometric conditions persisted for over 100 hours at a stretch

Abstract

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, on Ellesmere Island, Canada. Photometry of Polaris obtained in 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, October through March of 2008/09 and 2009/10, the sky near zenith had a mean surface brightness of 19.7 mag/square-arcsec when the sun was more than 12 deg below the horizon, reaching 20.7 mag/square-arcsec 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 hours 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.