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Can you see the Milky Way in the night sky where you live? There’s a good chance you cannot. Artificial lighting—from homes, streetlamps, cars, and other sources—pollutes 80% of the night sky across the globe, leaving one third of our population unable to see this majestic band of stars that stretches across our night sky. The problem is only getting worse: light pollution is increasing in North America and Europe by 6% each year. Fortunately, TEMPO, a new space-based instrument from the Center for Astrophysics | Harvard and Smithsonian, is monitoring how different types of light pollution are impacting our environment and our lives.

The Human and Environmental Impact of Light Pollution

Common pollutants, such as single-use plastics and chemical exhaust from factories, start as useful products like coffee cups and gasoline. It’s just when these products and their byproducts end up in the wrong place and begin damaging the environment that we start calling them pollutants. Similarly, light is not only useful, but life would not exist without it. But even light can become a pollutant if it’s shining in the wrong place at the wrong time. Not only does it disrupt our natural sleep-wake cycle, but it also disrupts the behaviors of wildlife that depend on light to navigate.

Light in cities and on coasts impacts several marine and land-based species. For instance, migrating birds that are normally guided by moonlight are attracted to artificial light; it causes them to fly in the wrong direction. Birds who follow trails of artificial light end up stopping in densely populated areas where higher levels of air pollutants damage their health. Also, when sea turtles hatch, they navigate in a seaward direction using natural light: the refection of celestial objects on the ocean’s surface guides them towards a safe habitat. But artificial light on coasts attracts sea turtles towards land where they become exposed to predators. Finally, the larvae of organisms such as marine worms, barnacles, and corals also use light to navigate towards habitats where they can settle and grow and, like with birds and sea turtles, these organisms can find themselves in the wrong place and their populations suffer as a result.

Artificial light also disrupts sleep in humans. Our brains use sunlight to determine when we should be awake, and the light from streetlamps interferes with these rhythms (not to mention the light emanating from our televisions and phones). Specifically, this light causes the brain to produce less melatonin, the brain chemical that makes us sleepy, leading people to sleep poorly and feel tired during the day. Research suggests that these effects can happen even with low levels of light—lower than the light produced by streetlamps. In fact, animal studies suggest that chronic exposure to dim light could weaken one’s immune system, but more research needs to be done to determine the effects of dim light on humans. In the meantime, artificial light makes it hard to even begin some scientific research.

If you live in a populated area, you’ll have trouble seeing stars in the sky due to skyglow, the light that forms when artificial light scatters in the atmosphere. For most of us, this just means the sky isn’t as pretty at night, but for astronomers, this means their job is more challenging than it used to be. In fact, a study published in late 2022 found that two thirds of ground-based telescopes are impacted by light pollution. That’s why astronomers today must build ground-based telescopes in remote regions of the planet, where there is minimal skyglow. For example, the Center for Astrophysics is currently building the Giant Magellan Telescope, the most powerful ground-based telescope ever constructed, in a remote part of the Atacama Desert in Chile, about 70 miles from the nearest city.

Why is the Center for Astrophysics Using TEMPO to Track Light?

TEMPO’s primary purpose is to track the origin, movement, and effects of all the major chemical pollutants in the air created by human activity and natural disasters to inform policy that improves public health. But given its impact on our environment and wellbeing, scientists will also track artificial light. Measurements of light will serve as a marker of human activity; TEMPO can also be used to monitor energy conservation efforts and compliance with outdoor lighting standards designed to reduce light pollution.

Currently, 19 states plus Washington, D.C. and Puerto Rico have passed laws with this objective. For example, many states require that outdoor lights be shielded to prevent light trespass, or light that shines where it is unneeded or unwanted. Other states require that light fixtures only emit as much light as necessary to cut down on energy waste and glare, the excessive light that hurts peoples’ eyes. Finally, some states like Florida passed laws to protect specific species such as sea turtles from artificial light, while others like New Hampshire have passed laws to preserve dark skies in rural areas. The Center for Astrophysics will make their data freely available to the scientific community and to government authorities, making it easier to track compliance with these laws to reduce energy costs, improve human wellbeing, and protect natural habitats.

TEMPO is the only space-based instrument that can distinguish between different lighting types across North America. For example, it can see the difference between mercury vapor, high- and low- pressure sodium vapor, and incandescent light, along with higher-efficiency LED lighting. It can also be used to help analyze lighting patterns in different regions and track the origins of the lights. It will give government authorities at the local, regional, state, and federal levels the information they need to understand the impact of light pollution within individual neighborhoods. Authorities can use these data to address specific concerns regarding individual buildings, properties, parks, or towns, or they can address light pollution at a broader scale to discover efficient and effective solutions that can impact the entire continent. Overall, TEMPO will enable scientists to study light pollution in new ways and discover pathways to clear and effective solutions that protect the environment and our own wellbeing.