Blue clouds, also known as night-shining clouds or Noctilucent clouds, are a normal occurrence that happens during late November or early December, particularly in Antarctica. Yet, surprisingly, the appearance of these blue clouds came a bit early, making it a new phenomenon, according to NASA.

"Noctilucent clouds are a relatively new phenomenon. They were first seen in 1885,' about two years after the powerful eruption of Krakatoa in Indonesia, which hurled plumes of ash as high as 80 km into Earth's atmosphere," stated Professor Gary Thomas from the University of Colorado in his article written in 2003 on NASA's website.

These noctilucent clouds are wispy clouds that shine a bluish-white light from viewers on the ground. But up in space, these clouds portray an intense shade of blue. Approximately a decade ago, a satellite by NASA snapped photos of the ice crystals which had formed these clouds. Based on the data from then-taken photos, the phenomenon of blue clouds had appeared earlier than expected.

The first sighting of the blue clouds was recorded in the middle of November. Images shown on NASA's website state that the photos of the noctilucent clouds captured in Antarctica were dated November 17 and November 28.

Under NASA's Aeronomy of Ice in the Mesosphere (AIM), the space agency hopes to study the noctilucent clouds to better understand the behaviour, climate, and the weather of the mesosphere. The satellite under the AIM project was launched back in 2007 and is the ninetieth NASA exploration and research mission which is part of the Small Explorer Program (SMEX)

As where noctilucent clouds are concerned, the early appearance of these blue clouds is said to be caused by the presence of greenhouse gases. On this note, scientists believe that the clouds are a signal of global warming. On the other hand, a few claim that these blue clouds are simply space dust remnants in the atmosphere, which is one theory NASA supports.