MCAS Practice Test 7

“Reclaiming the Dark” by Beatriz Calloway

¹Step outside on a clear night in most American towns and look up. You will probably see the moon, a scattering of bright stars, perhaps a planet. What you almost certainly will not see is the Milky Way—the faint, glowing band of our own galaxy that stretched across the sky for nearly every human generation until about a century ago. For many people alive today, it is something seen only in photographs.

²The cause is light pollution: artificial light that spills beyond where it is needed and into the sky. Streetlights, parking-lot fixtures, illuminated signs, and the glow of windows add up. Light scattered by particles in the atmosphere creates “skyglow,” a dull orange or gray dome that can be seen from many miles away. A 2016 atlas of night-sky brightness estimated that the Milky Way is hidden from more than a third of humanity, including nearly 80 percent of North Americans.

³And the problem appears to be growing. Satellite instruments have trouble detecting some kinds of modern lighting, so researchers have turned to ordinary people for help. In one long-running project, volunteers around the world step outside, compare the stars they can see with a set of charts, and report the faintest ones visible. After analyzing tens of thousands of these reports, scientists estimated in 2023 that the night sky had been brightening by nearly 10 percent a year. At that rate, the sky's brightness would double in less than eight years.

⁴Losing the stars might sound like a concern only for stargazers, but researchers say the effects reach much further. Many animals depend on darkness. Sea turtle hatchlings find the ocean by crawling toward the brighter horizon over the water; near brightly lit beaches, they may crawl inland instead. Migrating birds, many of which travel at night, can be drawn toward illuminated buildings, where they circle until exhausted or collide with glass. Insects swarm around outdoor lights by the millions, a pattern some scientists suspect contributes to declines in insect populations.

⁵Humans may be affected too. Our bodies keep time partly by responding to light and dark, and exposure to bright light at night can disrupt sleep. “We evolved under a sky that was dark for half of every day,” says Harlan Duquette, an astronomer who has studied skyglow for two decades. “We've changed that in about four generations. It would be surprising if that had no consequences.”

⁶Unlike many environmental problems, though, light pollution can be reduced quickly. Light does not linger in the environment the way chemicals or plastic do. Switch off a fixture, and its contribution to skyglow ends instantly. That fact gives dark-sky advocates an unusual kind of optimism. “This is one of the few problems where the solution is literally at our fingertips,” Duquette says.

⁷The solutions are not complicated. The first is shielding: fixtures designed to point light downward, toward the ground where people need it, rather than sideways and up. The second is using only as much light as a task requires, since many parking lots and signs are lit far more brightly than safety demands. The third is timing. Lights on motion sensors or timers shine when someone is present and switch off when no one is. Finally, color matters. Many cities have replaced older streetlights with energy-efficient LEDs, which saves money and electricity. But some early LEDs gave off a harsh blue-white light, which scatters more in the atmosphere and is more disruptive to wildlife than the warmer, amber-toned light that newer fixtures can produce.

⁸A few communities have built their identities around protecting the dark. An international organization certifies “dark-sky places”—parks, reserves, and towns that adopt strict lighting rules and teach residents about night skies. Some of these places now draw visitors who travel hundreds of miles to see the Milky Way for the first time. Jolene Kaminski, who helped lead her small town's effort to earn the designation, recalls the first public stargazing night after new streetlights were installed. “A man in his sixties stood next to me and said, ‘I haven't seen that since I was a boy,’” she says. “Then he just stood there, looking up, for a long time.”

⁹Change is not always easy. Some residents worry that dimmer streets will be less safe, and business owners may fear that customers will not notice shops that are not brightly lit. Researchers say the relationship between lighting and safety is more complicated than it seems: glare from poorly designed lights can create deep shadows and actually make it harder to see. Well-shielded lighting, they argue, can improve visibility while sending less light into the sky. Still, advocates admit that persuading people to accept less light requires patience and evidence, not just enthusiasm.

¹⁰Kaminski thinks the hardest part is that most people do not know what they are missing. “You can't miss a sky you've never seen,” she says. “Once people see it, the argument mostly makes itself.”