The summer of 2017 was pretty special for lots of people living in North America. On August 21st, a total solar eclipse was visible across a huge swath of the United States, and anticipation for the event was huge not only among the general public but also in the scientific community. Now, researchers are revealing that they observed something that happened during the eclipse that had never been detected before, and it’s incredibly interesting.

As the moon’s shadow blotted out the Sun’s rays on that midsummer day, thousands of sensors picked up some odd behavior in the atmosphere. The moon’s shadow, speeding across the Earth’s surface, actually created ripples in Earth’s atmosphere like a boat moving through water.

Scientists from the United States and Norway utilized data on satellite positions to show that the Earth’s atmosphere rippled like a pond as the eclipse passed over the planet. That bizarre effect has been attributed to the heat energy bombarding the atmosphere from the Sun, rapidly cooling and then heating up again as the moon’s shadow passed over it. The research was published in Geophysical Research Letters.

“During solar eclipses, the moon’s shadow causes a large reduction in atmospheric energy input, including not only the stratosphere but also the thermosphere and ionosphere,” the study explains. “The eclipse shadow has a supersonic motion which is theoretically expected to generate atmospheric bow-waves, similar to a fast-moving river boat, with waves starting in the lower atmosphere and propagating into the ionosphere.”

This behavior was vaguely theorized in the past but never adequately measured or demonstrated via hard data, until now.