Sky brightness at the Kitt Peak National Observatory

Abstract

We report results of a program to determine the brightness of the night sky at Kitt Peak during the recent solar minimum. Well-calibrated photometry in B and V suggests that the average brightness of the night sky during this period was approximately V = 21.9, B = 23.0 in magnitudes per square arc second but that variations of a few tenths of a magnitude can occur from night to night, or even during a single night. Since 1987 the sky has already brightened considerably, probably due to the increase in solar activity as the Sun moves toward sunspot maximum in 1991.

The spectrum of the Kitt Peak night sky

“…On 1988 February 18 the zenith sky varied by a few tenths of a magnitude/arc sec 2 ; such fluctuations are also found in the data of Pilachowski et al (1989) andWalker (1988). On this night it was indeed "darkest before the dawn", at least at the zenith.…”

“…Walker (1988) found a good correlation of zenith sky brightness with solar activity where the latter was measured by the "decorrected" Ottawa 10-cm flux (e.g., not referred to 1 AU but to the Earth's actual distance from the Sun) as determined on the previous UT day. Pilachowski et al (1989) found a similarly excellent correlation for their measurements. We show in Figure 2 from the Solar-Geophysical Data prompt reports (1988).…”

“…During the next decade the distribution of light among these three sources may well change as Tucson and Pima County convert to LPS lighting and 4000 4500 5000 5500 6000 6500 Wavelength (A) The sky brightness increases by a few tenths going from the zenith to a zenith distance of 60°. On some of the 12 nights of data used by Pilachowski et al (1989) the change in sky brightness with respect to zenith distance was steeper than that; on other nights it was flatter. It is interesting to note from our data in Table 2 that the flux in each set of emission lines tracks well with the increase in continuum level (e.g., the relative contribution to the sky brightness remains nearly constant with respect to zenith Figure la we can see that the Hg lines are somewhat stronger relative to the continuum at a zenith distance of 60° than at the zenith, but the effect is quite small.…”

“…This question is of timely importance given the plans for construction of new4-m class telescopes on the mountain. Pilachowski et al (1989) have recently published the results of photoelectric photometry of the KPNO night sky. These observations were made near solar minimum (which occurred in 1986) and should therefore reflect the best the site can currently offer.…”

Night-sky brightness monitoring in Hong Kong

“…On the other hand, this figure does present a characteristic level of night-sky brightness in Hong Kong as the survey covered a wide variety of locations and a wide range of time frames under diverse natural and artificial conditions. The current level is significantly brighter than the natural NSB level of 21.6 mag arcsec −2 (a 5.5-mag arcsec −2 difference, or 160 times brighter in flux) recommended by the International Astronomical Union for conducting astronomical observations (Smith 1979), not to say the darker skies of 21.7-22.0 mag arcsec −2 measured at research observatory locations (Pedani 2009;Patat 2008;Sanchez et al 2007;Krisciunas et al 2007;Pilachowski et al 1989). On the other hand, the darkest sites in Hong Kong at 20.8 mag arcsec −2 remain to be reasonably good sites for public enjoyment on the starry night and for astronomy work despite the heavy urbanization in many parts of the city and it is essential that efforts should be made for these locations to remain so as discussed in "Introduction".…”