Why the Night Sky is Not Inky Black (Sorry, Poets)
Atmospheric scattering sheds light on a variety of strange phenomena
On the night of the new moon* I awoke around midnight to assure myself that I was seeing things. I was.
On the darkest night of the month, with no moonlight, I could still see black silhouettes of trees on the horizon. I took in grassy fields distinctly less dark than the trees. I saw a gray sky, even paler than the grass. The sky wasn’t black at all.
Hawaii has regulated and reduced light pollution to preserve conditions so that mountaintop observatories can continue to explore the cosmos. When I moved to the Big Island two years ago, friends told me to expect to be impressed by the darkness of the night skies.
I was struck by the opposite. Hawaiian night skies don’t plunge you into blackness, they bathe you in a special light. Zillions of stars are visible, but the pinpricks of light don’t seep through a backdrop of inky black, or ebony, or obsidian. The sky is a not-particularly-dark gray. Except for a few nights each month, several hours before sunrise I can safely walk or run on rural roads devoid of any streetlights.
It wasn’t until my recent trip to view a solar total eclipse that it dawned on me how important atmospheric scattering is…
