Diversions: Light Pollution and London
Nighttime skies in San Diego are less lit than in some other cities, but it's still a shock when you get outside the city at night and see the tapestry of stars overhead. There is a good piece on the subject in the current National Geographic, and it contains this fascinating observation:
For most of human history, the phrase "light pollution" would have made no sense. Imagine walking toward London on a moonlit night around 1800, when it was Earth's most populous city. Nearly a million people lived there, making do, as they always had, with candles and rushlights and torches and lanterns. Only a few houses were lit by gas, and there would be no public gaslights in the streets or squares for another seven years. From a few miles away, you would have been as likely to smell London as to see its dim collective glow.
More here.
