Chaco is the 13th park in the U.S., Hungary, England and Scotland to receive the designation from the International Dark-Sky Association. The organization also recognizes reserves and communities that protect the night sky.
The Albuquerque Astronomy Society last year nominated Chaco for the designation. At the time, Dee Friesen was president of the group.
"It's an opportunity for Chaco to show off its night sky," he said of the designation after he set up a telescope for stargazing near Chaco's amphitheater on Thursday night.
He was accompanied by other members of the group, including Gordon Schaefering, who moved to Santa Fe last year from New York.
"I think people miss the beauty of what's out there," Schaefering said, commenting that many people never see the Milky Way galaxy or planets like Saturn or Jupiter.
Aesthetics aside, the dark sky is important because of its effect on ecosystem and human health, said Nathan Ament, coordinator for the Colorado Plateau Dark Skies Cooperative. He said studies on women who work night shifts have shown the late-night hours can lead to an increased rate of breast cancer.
In addition to health, the night sky has been important to Chaco since the time the kivas were first built in A.D. 900 and 1150.
"What we're doing tonight is maintaining a very ancient tradition," said Great Bear Cornucopia, an interpreter at Chaco.
Cornucopia said the sky influenced the Chacoans, and people who visit the park today to see the stars connect with the area's history.
"We have a direct link from the world we live in to the world the Chacoans lived in," Cornucopia said.
Tyler Nordgren, a professor at University of Redlands in California, approached Cornucopia in 2007 about documenting the night sky in Chaco. Since then, Nordgren has traveled to many national parks to observe both the stars and light pollution. He authored "Stars Above, Earth Below" about the night skies in the parks.
Nordgren, who is also a member of the board of directors of the International Dark Sky Association, spoke at Chaco's dedication ceremony at dusk on Thursday.
Prior to working as a professor in California, Nordgren worked at an observatory in Flagstaff, Ariz., where he first encountered truly dark skies. After moving to Los Angeles, he recalled his first night in the populated city. When the sun set, the familiar stars were not visible.
"It's like the sky I knew had just disappeared," he said.
Seven years later, Nordgren took a sabbatical from work. While many astronomers spend their sabbaticals at observatories and writing papers, Nordgren opted to document the night skies of the national parks.
Nordgren told the audience on Thursday that most people today can no longer see the natural night skies.
"The Milky Way had become a symbol of something different, like grizzlies and glaciers and granite cliffs," he said.
But, he said, there is a lot that people can learn from the stars, including the Milky Way Galaxy. He described the galaxy as 100 billion stars crammed into a giant pinwheel.
"We live inside that great, big pinwheel," he said.
By observing the stars, astronomers determined the Earth is not located at the center of the galaxy. Because of this, the Milky Way is most visible during the summer when the earth is looking toward Sagittarius at the center of the galaxy. In the winter, the earth looks toward Orion and away from the center.
Nordgren also spoke about ancient astronomy at Chaco.
"Our ideas of time and location and direction all come from the stars," Nordgren said.
As an example, he pointed to the kivas in Chaco that align with true north. He said the kivas were likely built by looking at where the shadows point when the sun is at its highest point in the sky.
Nordgren explained the sun was also important to Chacoan culture because it helped them decide when to plant. One petroglyph at Chaco has even been interpreted as depicting a solar eclipse.
The sky still remains an important aspect of Chaco Culture National Historical Park, But, Nordgren said, light pollution from cities like Albuquerque, Gallup and Grants is starting to encroach on the night sky.
Other national parks have already lost their night skies, Nordgren said. He showed a picture of Arches National Park in Moab, Utah, at night with the light from the city reflecting off of the rock formations.
"We've banished darkness from this park," he said.
Nordgren said light pollution can be stopped almost instantly by taking a few steps, such as modifying street lamps. With a typical street lamp, 50 percent of light is reflected up into the sky and another 10 percent is reflected horizontally. Nordgren said this light is wasted electricity and adds to the carbon footprint.
If cities replace their street lights, he said, they should consider putting shades on the lights, to direct the light downward. These types of lights are sold in stores as good neighbor lights for people wanting to modify their house lights.
"We can get our stars back," Nordgren said.