DENVER (CBS NEWS) – Social media speculation was sky high over the weekend after a line of flashing lights was seen above the Denver area. At first glance, many saw a convoy of flashing lights lined up in a straight formation.

On Twitter, some speculated the line of lights were part of UFOs. Others were curious if they were drones.

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According to a military spokesperson, the lights actually belonged to a convoy of C-17 aircraft that were involved in an exercise. CBS Denver was told the planes were headed from South Carolina to Nevada and back.

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Aviation expert Steve Cowell says the planes were flying in a formation that is commonly seen in military exercises.

“That was the echelon formation. In other words, they were all lined up in a row,” Cowell said. “It is not uncommon to have these types of planes in formation, especially at night. Often times, you will see them doing this, especially when they are doing training flights, or standard cross country procedure.”

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