UBVRItwilight sky brightness at ESO-Paranal

Abstract

Context. Twilight studies have proved to be important tools for analyzing the atmospheric structure with interesting consequences on the characterization of astronomical sites. Active discussions of this topic have started again recently in connection with the evaluation of Dome C, Antarctica, as a potential astronomical site and several site-testing experiments, including twilight brightness measurements, are being prepared. Aims. The present work provides the first absolute photometric measurements of twilight sky brightness for ESO-Paranal (Chile). They are meant both as a contribution to the site monitoring and as reference values in the analysis of other sites, including Dome C. Methods. The UBVRI twilight sky brightness was estimated on more than 2000 FORS1 archival images, which include both flats and standard star observations taken in twilight and covering a Sun zenith distance range 94• -112• . Results. The comparison with a low-altitude site shows that Paranal V twilight sky brightness is about 30% lower, implying that some fraction of multiple scattering has to take place at an altitude of a few km above sea level.

Airglow and Aurorae from Dome A, Antarctica

“…Figure 14 shows the flux versus ζ ⊙ for a single wavelength. A visual comparison with similar data and models presented in Patat et al (2006) reveal that the sky does indeed darken faster at Dome A, supporting the idea that multiple scattering is less effective for sites on the Antarctic plateau. The amount of annual dark time and solar zenith distance at which twilight ends, ζ D , as a function of wavelength, is given in Figure 15.…”

“…The formal definition of astronomical night time is when the solar zenith distance, ζ ⊙ , reaches 108°, which, for some observing locations, suffices as an adequate description. For more exceptional sites, such as La Silla Paranal Observatory in the Atacama desert in Chile, a definition of ζ ⊙ ¼ 105°is more appropriate (Patat et al 2006). At high latitudes, where the amount of usable dark time is critically dependent on this value (e.g., Zou et al 2010), it is important that this point is defined accurately.…”

Contributions of artificial lighting sources on light pollution in Hong Kong measured through a night sky brightness monitoring network

“…However, based on actual measurements of the sky brightness taken near summer and winter solstices, it was concluded the conditions could be slightly relaxed to 70 minutes after sunset and 70 minutes before sunrise, due to obstructed near-horizon sightlines reaching the light sensors. While these sunlight-affected entries, making up 40% of all collected, would be excluded for NSB studies, they could potentially be used in the future for studies of atmospheric optical properties through changes in the sky brightness level during twilight (Patat et al 2006;Rozenberg 1966;Hulburt 1953).…”

Detection of Leonids meteoric dust in the upper atmosphere by polarization measurements of the twilight sky

“…It will also give more information about the altitude distribution of meteoric dust. Since the sky brightness during the dark twilight is basically contributed by troposphere multiple scattering and depends on the altitude of the observation place (Patat et al, 2006), the observations are better to conduct in the mountain sites, where this background is lower. …”