Astronomers report that nearly a fifth of the world's population cannot see the Milky Way band thanks to light pollution. While the condition may seem to simply be a loss of nocturnal aesthetics, researchers believe it actually affects human health by disturbing the circadian rhythms that drive sleep patterns. Some studies have even linked unnatural levels of light affecting hormone levels (specifically in conjunction with rates of breast cancer). Regarding the light pollution itself, even bouncing just 3% of city's lights into the sky can increase observable sky glow by up to 10% from 100km away. Cities that reflect 10% of their light skyward increase that same sky glow by 570%.