These noctilucent clouds, or polar mesospheric clouds (PMCs), form in the summer, when ice crystals come together on tiny meteor particles in the mesosphere. The result is long blue and white clouds, visible just after the sun sets.

Using a giant balloon equipped with seven imaging systems, NASA collected 6 million high-resolution photos of this natural phenomenon. The PMC Turbo balloon left Sweden in early July and landed in Canada five days later, but the photos are just now being publicly released.

By observing polar mesospheric clouds, NASA’s PMC Turbo mission is helping scientists better understand turbulence in Earth’s upper atmosphere: https://t.co/7BtELvKnvP pic.twitter.com/zrSb9RMFJ9

— NASA Goddard (@NASAGoddard) September 20, 2018

While the clouds are beautiful, NASA’s scientists are more interested in the forces that shape them. Uplifting air masses, such as when air is pushed up by mountains, transfer energy from the lower atmosphere to the mesosphere. They’re known as gravity waves, and understanding their movement can help scientists better model the turbulence of oceans, lakes, and other planetary atmospheres. It could also aid weather forecasting.

“From what we’ve seen so far, we expect to have a really spectacular dataset from this mission,” said Dave Fritts, principal investigator of the PMC Turbo mission, in a statement. “This is the first time we’ve been able to visualize the flow of energy from larger gravity waves to smaller flow instabilities and turbulence in the upper atmosphere.”

“At these altitudes you can literally see the gravity waves breaking—like ocean waves on the beach—and cascading to turbulence,” he added.

In addition to the images, the PMC Turbo mission used a lidar, or laser radar, to measure the clouds’ altitudes and the temperature changes in the gravity waves above and below them, aiding in determining the structure of the waves.