Night sky brightness is a major source of noise both for Cherenkov telescopes
as well as for wide-angle Cherenkov detectors. Therefore, it is important to
know the level of night sky brightness at potential sites for future
experiments. The measurements of night sky brightness presented here were
carried out at Fowler's Gap, a research station in New South Wales, Australia,
which is a potential site for the proposed TenTen Cherenkov telescope system
and the planned wide-angle Cherenkov detector system HiSCORE.
A portable instrument was developed and measurements of the night sky
brightness were taken in February and August 2010. Brightness levels were
measured for a range of different sky regions and in various spectral bands.
The night sky brightness in the relevant wavelength regime for
photomultipliers was found to be at the same level as measured in similar
campaigns at the established Cherenkov telescope sites of Khomas, Namibia, and
at La Palma. The brightness of dark regions in the sky is about 2 x 10^12
photons/(s sr m^2) between 300 nm and 650 nm, and up to four times brighter in
bright regions of the sky towards the galactic plane. The brightness in V band
is 21.6 magnitudes per arcsec^2 in the dark regions. All brightness levels are
averaged over the field of view of the instrument of about 1.3 x 10^(-3) sr.
The spectrum of the night sky brightness was found to be dominated by longer
wavelengths, which allows to apply filters to separate the night sky brightness
from the blue Cherenkov light. The possible gain in the signal to noise ratio
was found to be up to 1.2, assuming an ideal low-pass filter.Comment: 9 pages, 9 figures. Accepted for publication in Advances in Space
Research as Proc to COSPAR 201
