The Lick Observatory is one of the oldest observatories still in operation today. At 128-years-old, this gateway to the stars has seen the rise of one of America's largest cities. The observatory is located about 25 miles away from San Jose, California. Over the past decade the city has seen enormous growth. Today, its lights illuminate the night sky for miles, and that is a big problem for the Lick Observatory.
When light pollution started to disrupt the effectiveness of Lick’s telescopes, the city of San Jose took steps to make a change. In 1980, the city issued a light pollution ordinance and replaced its bright mercury vapor lights with low-pressure sodium lights. These lights give off a yellow hue which is easier for astronomers to filter out because they’re monochromatic. But today, the city is making another change to its street lights, and it's bad news for astronomy.
In an effort to appease its residents who are not fans of the yellow lights, San Jose is installing new LED lights across the city. The white LEDs emit multiple bands of color, essentially mimicking sunlight. The glow from LEDs is nearly impossible to filter out entirely. To help ease the brightness, the city says it will dim the lights late at night when the observatory is most active. And while that will help, Lick astronomers are finding ways to adapt to the changing environment, like focusing on making observations using near-infrared astronomy, which isn’t impacted by the optical wavelengths emitted by light pollution. It’s one of many solutions that are still far from ideal. Because, as San Jose continues to grow, new lights will turn on every day. And for astronomers, the best light is no light at all.