Just before the sun dips below the horizon, sometimes a brilliant green or blue flash appears at the edge of the fiery ball. To see it, you have to be somewhere with an unobstructed view of the sun and a very stable atmosphere.

Image courtesy and copyright Stéphane Guisard, www.astrosurf.com/sguisard

The perfect spot is the Cerro Paranal Observatory in Chile, perched on a 2,635-meter (8,645-foot) mountain in the Atacama Desert, where they get an average of 300 cloudless days per year. Check out these images, as well as another solar phenomenon called a “Gegenschein.”

The observatory, which is operated by the 13-nation European Organisation for Astronomical Research in the Southern Hemisphere (ESO), is home to the Very Large Telescope (yes, that’s the official name), which ESO describes as the world’s most advanced optical instrument.

The green and blue flashes happen when Earth’s atmosphere acts as a giant prism, refracting certain colors from the setting sun’s rays. It’s a tradition at Paranal for the staff to gather at sunset every day to watch for the flashes before settling down for a night of astronomical observations, according to the ESO Web site.

But kids, don’t try this at home - at least not without proper eye protection. The ESO site emphasizes that looking at the sun with the naked eye is dangerous, and looking at it through a camera, binoculars, or telescope is even worse. “Do not attempt to observe the Sun unless you know what you are doing,” the site warns repeatedly.

–Kate King, Writer, cnn.com