From the Ground Up II: Sky Glow and Near-Ground Artificial Light Propagation in Flagstaff, Arizona

We present panoramic sky brightness measures in the Johnson V V band made at the US Naval Observatory Flagstaff Station. We find that these measures show much less sky glow from Flagstaff than expected using the total light output and unshielded fraction determined recently by Luginbuhl et al. and Garstang’s 1991 modeling approach. We suggest the difference arises principally from the diminution of upward-directed light after emission from light fixtures and reflection from the ground due to interaction with structures and vegetation. This interaction not only reduces the effective albedo, it also disproportionately reduces flux emitted upward at angles near the horizontal. We explore the size and consequences of this factor in light pollution modeling, and propose a modified upward angular distribution function to account for this effect.