In 1888, Vincent van Gogh wrote to his brother, Theo, “For my part I know nothing with any certainty, but the sight of the stars makes me dream, in the same simple way as I dream about the black dots representing towns and villages on a map. Why, I ask myself, should the shining dots in the sky be any less accessible to us than the black dots on the map of France?”
Van Gogh was lucky enough to witness a majestic night sky that people today can rarely experience. According to the journal Science, 83% of the world’s people live under skies polluted with light, creating a “skyglow” that hides the stars. In the United States, that number is 99%.
Today, there is so much light in the Cambridge area that we see only a fraction of the stars in the night sky and we usually cannot see our own galaxy, the Milky Way. On cloudy nights when artificial lights are reflected back toward earth, our skies are hundreds or thousands of times brighter than they were merely 200 years ago. (This probably explains why I can walk around my house in the middle of the night without turning on lights.) Can you imagine what van Gogh’s “The Starry Night” would have looked like if he saw only a fraction of the stars in the sky?
The artificial brilliance of the night sky is problematic for more than just artists. All life on earth relies on the natural cycle of light and dark, which occurs when the sun sets and the moon and stars become visible. This light-dark cycle has evolved over billions of years to optimize the health of living organisms, including reproduction, sleep, food availability, and protection from predators.
But humans, going back to the Moors in Spain who used oil lamps to illuminate their streets, have altered this natural process, affecting the natural world.
Take moths. At night, moths fly from flower to flower feeding on nectar, much like bees do during the day. Moths pollinate about one-third of our flowering plants. In fact, moths are faster pollinators than bees, and they pollinate some flowers that bees do not even visit. Moths evolved to use the moon to orient themselves when flying at night. When they encounter a porch light, for example, they think the bulb is up. They turn their backs toward this light and fly in circles around the bulb in an attempt to stay level. But just the opposite happens: By keeping their back oriented toward the light, they fly in erratic circles until exhausted, leaving flowers unpollinated.
Like moths, about 70% of mammals are nocturnal, evolving roughly 225 million years ago into tiny shrew-like creatures that did their best to elude the giant, day-dwelling dinosaurs. Most mammals today are still small nocturnal creatures. And artificial light inhibits their behavior as well.
For example, small mammals such as mice eat less food in areas lit by artificial light (presumably to avoid predators). Artificial light affects the circadian rhythm, the internal 24-hour clock of both nocturnal and diurnal mammals, suppressing melatonin production, resulting in poor sleep, increased stress, more cardiovascular problems, and an increased chance of tumors.
Artificial light also affects amphibians, reptiles and marine life. Frogs and toads croak at night as their mating call. Artificial light disrupts the frequency of these calls, interfering with their reproduction. Sea turtle hatchlings head toward the brightest light, which used to be the moonlit ocean. But now white, bright lights from beachfront properties pull them in the wrong direction. Heading toward these lights leads them into the path of predators, causes dehydration and even death. Fish rely on lunar cycles to migrate and spawn. Artificial light near bodies of water alters their migration timing and reproductive success.
Despite being nocturnal animals, bats and owls need low-light levels to locate and capture prey. The bright glow of artificial lights confuses their sensory cues, disrupting their ability to find food. Lights at night can also cause fireflies, which use their flashes to find mates, to fail to reproduce.
Our use of artificial lights has increased over the last century, leading millions of migrating birds to travel off course, fly into buildings, or migrate too early or too late. For hundreds of years people noticed that migratory songbirds, such as red-eyed vireos, palm warblers, and hermit thrushes, were attracted to the lights beaming out of lighthouses, especially on foggy nights. Today, palm warblers are one of the most frequently killed at lighted towers across the United States. One TV tower in Florida killed more the 44,000 birds in a 29-year period, including 2,305 palm warblers.
Artificial lights cause harm in all these ways and more. But we can do something about this. The Cambridge city council has recognized that thoughtful lighting policy protects public health, conserves energy, and preserves the natural environment. It has declared April 13–20, 2026, to be International Dark Sky Week.
Observing Dark Sky Week could involve limiting the nighttime use of lights so as not to disorient insects and birds during their spring migration. We can close our blinds or curtains at night to prevents stray light from spilling out. We can use motion detector lights when possible, so lights are on only when needed. We can cover outdoor lights so they shine downward and not upward. Focused light attracts fewer insects. We can also work to encourage governments to adopt responsible lighting practices.
By restoring natural lighting conditions, we can help preserve our nocturnal ecosystems and protect species that depend on darkness. And maybe give rise to a future Van Gogh’s own star-inspired work of art.
A stronger
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