Arizona became a center for astronomy in the early 20th century because of its clear, dark skies. The cities were small, remote mountaintops were plentiful, and clouds were rare. The state boasted up to nine months a year of near-perfect conditions for astronomy.

In part four of Collecting Light: An Exploration of Arizona Astronomy, we look at efforts to preserve Arizona’s dark skies, even as light pollution from the state’s metropolitan areas expands into even the most remote areas.

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Today, rapid population growth in Phoenix and Tucson is blotting out the darkness. “Light domes” over both metro areas now affect telescopes more than 100 miles away.

Headlight blinders to protect telescopes
Cars at Kitt Peak National Observatory are assigned headlight blinders to reduce light pollution around the sensitive telescopes. (Photo: Mark Duggan)

In response, astronomers have begun building the next generation of large telescopes in Chile.

The Atacama Desert, high-elevation and mostly-uninhabited, provides the same ideal viewing conditions today that Arizona did a century ago. It’s considered to be the driest place on earth.

And from a scientific perspective, it also lets astronomers make detailed observations from the Southern Hemisphere.

While Phoenix and Tucson continue to boom, creating more light pollution, another city is moving in the opposite direction. Flagstaff was one of the first certified “International Dark Sky” cities, which is remarkable considering that it’s a community of about 70,000 people. But Flagstaff enacted specific lighting ordinances to protect area observatories. The sky over the northern Arizona city lacks the light dome that similar-sized cities project skyward.

Tucson skyline at dusk
The Tucson skyline from the Mt. Lemmon Highway. Kitt Peak National Observatory is on a mountaintop in the background, less than 40 miles from the city. Light pollution is increasingly affecting observations at telescopes on both Kitt Peak and Mt. Lemmon. (Photo: Mark Duggan)

International Dark Sky certification comes from the Tucson-based International Dark Sky Association. They work with states, communities, and even lighting manufacturers to preserve dark skies.

But it’s sometimes an uphill battle, as some communities resist efforts to reduce lighting out of safety concerns. And making the argument that light pollution makes it harder for astronomers to see a galaxy billions of light-years away can be a tough sell.

Collecting Light: An Exploration of Arizona Astronomy is an audio documentary series looking at the past, present, and future of both professional and amateur stargazing in the state.

See a gallery of photos from the series here. Listen to the other episodes now:

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