Humans are not nocturnal creatures. Our eyes have adapted to living in the light, and over the last few hundred years, we have slowly brightened the night so we can inhabit it more freely. Half the world is haloed in networks of light that shine so brightly they can be seen in space, but while they may look beautiful from above, there are consequences. Badly-designed lighting often shines light in all directions instead of just where it’s wanted, and this extra light washes out the darkness and pollutes the sky with brightness, altering natural light levels. Because light is such a powerful biological force, this messes with the rhythms animals including ourselves have adapted to—for example, birds migrating at night become disoriented by unnatural light, and are especially apt to collide with brilliantly-lit buildings. The vacant orange haze that light pollution casts across the sky also empties it of stars. This is why most observatories are located in isolated places, which is sad because the average person can no longer lift their eyes to see the universe above—the infinite canvas of stars and planets and galaxies is unknown to them. Remedying this pollution is relatively simple: altering the design of light installations can immediately block wasted light, helping to save energy and reduce carbon dioxide emissions. Flagstaff, Arizona, made one of the earliest efforts to minimise light pollution to protect the nearby Lowell Observatory, and it became the first International Dark Sky City in 2001. Many other places have made the same efforts and have become Dark Sky Preserves—sanctuaries free from artificial light, where the darkness is kept so pristine that the universe soars above.