Night Sky Brightness at Cerro Pachon

A Sky Brightness Primer

The natural night-sky brightness is made up from several components. From Benn & Ellison, La Palma report 114, and for the V band at zenith:

The calculation of the amount of light pollution at a given site has been treated by Garstang (PASP 101, 306, 1989a) and the evolution with time discussed by Garstang (ARAA, 27,19, 1989b). Here we show (Figure 1) an example the contributions from direct light, scattering by aerosols, and Rayleigh scattering by molecules vary as a function of zenith distance, calculated by Garstang (1989) for Mt. Graham.

Figure 1

It is often not appreciated that the brightness of the night sky varies around the solar cycle, with a B or V-band peak-peak of over half a magnitude, This is well shown (Figure 2) by Krisciunus (PASP, 109, 1181, 1997) for Mauna Kea.

Figure 2

Predicted man-made contributions for several observatories that have strong light pollution are shown in Figure 3, from Garstang (1989b). Note that the solar cycle modulation of 0.6 mag amplitude has been removed. The pollution growth models are based on population estimates and assume that no attempts are made to reduce the light output per person by installation of environmentally friendly light fixtures, etc.

Figure 3