The photo above shows the moon rising over Maine's Casco Bay on July 10, 2017. The satellite took on a rectangular appearance, a mirage scientists say was caused by cold air.

(Courtesy of John Stetson/Southern Maine Community College)

At a Glance

A rising moon looked like a giant block of ice as it appeared in the sky over Casco Bay in Maine. Scientists say the phenomenon was caused by cold air.

A rising full moon shocked skywatchers when it appeared as a rectangleabove Casco Bay in Maine on Monday evening.

",” skywatcher and Southern Maine Community College adjunct instructor John Stetson told Spaceweather.com. “Faint and shaped like a giant block of ice.”

The phenomenon sparked rumors of alien activity, but scientists determined that cold air is the culprit behind the mirage.

A closer view of the "rectangular" moon that appeared over Maine's Casco Bay on July 10, 2017.

(Courtesy of John Stetson/Southern Maine Community College)

(MORE:)

At the time of the moon rising around 8:30 p.m., the ocean’s temperature was at 58 degrees Fahrenheit, while the surrounding air was 75 degrees, according to weather.com meteorologist Jonathan Belles.

“The cold sea offshore of Maine cooled the air above it,” atmospherics optics expert Les Cowley told Spaceweather. “Above that was warmer air, atemperature inversionand the stuff of mock-mirages. The moon's rays passing through it bend and twist into several moon images, some upright some inverted. They combine together into the rectangular 'iceberg.’”

In August, the will appear in the sky over parts of America. For roughly two minutes, the moon will completely block the sun and turn the daytime into an eery, dark twilight.

MORE ON WEATHER.COM: Full Moons