Multiple Green Flashes at Sunset: Chilean Mountaintop View

Multiple Green Flashes at Sunset: Chilean Mountaintop View

From the high altitude of the Cerro Tololo Inter-American Observatory (CTIO) in Chile (2,200 meters or 7,200 feet), two astrophotographers captured the elusive sunset phenomenon known as the green flash. This stunning trick of light occurs at sunset and sunrise when light from the Sun travels through the thickest part of Earth’s atmosphere. Acting like a prism, Earth's atmosphere bends, or refracts, the light and separates it into its component wavelengths. Blue and violet light are scattered by the atmosphere, while red, orange and yellow are refracted below the solar disk below the horizon, leaving the green light the most visible during the few seconds that the Sun disappears below the horizon. 

Here, though, is another uncommon phenomenon. Distinct thermal layers above the Pacific Ocean led to a Fata Morgana mirage displaying several green flashes.

A Fata Morgana is a complex form of mirage visible in a narrow band right above the horizon. The term Fata Morgana is the Italian translation of "Morgan the Fairy" (Morgan le Fay of Arthurian legend). These mirages are often seen in the Italian Strait of Messina, and were described as fairy castles in the air or false land conjured by her magic. Fata Morgana mirages significantly distort the object or objects they are based on, often so that the object is completely unrecognizable. A Fata Morgana may be seen at sea or on land, in polar regions, or in deserts. It may involve almost any kind of distant object, including boats, islands, and the coastline. Often, a Fata Morgana changes rapidly. The mirage is made up of several inverted (upside down) and upright images stacked on top of one another. Fata Morgana mirages also show alternating compressed and stretched zones.

Mirages are optical illusions caused by the refraction of light rays through layers of air with varying temperatures and densities. They commonly occur in hot environments, such as deserts or over bodies of water, where the air near the ground is significantly warmer than the air above it.

Credit: CTIO/NOIRLab/NSF/AURA/T. Slovinský & P. Horálek (IoP Opava)
Release Date: March 28, 2023

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