On Cerro Paranal, the 2600-metre-high mountain in Chile’s Atacama Desert, home to the European Southern Observatory (ESO) Very Large Telescope, the atmospheric conditions are so exceptional that fleeting events such as the green flash near the setting sun are not that uncommon. Now, however, ESO Photo Ambassador Gerhard Hüdepohl has captured a rare sight: a green flash seen near the moon. The photographs are likely the best ever taken of a green flash visible from Earth, as seen on the edge of the moon.
Hüdepohl was surprised and delighted to catch the stunning green flash in this series of photographs of the setting full moon crossing the horizon, taken on a clear early morning from the Paranal Residencia. Hüdepohl is a renowned landscape photographer who likes to incorporate the night sky into his work.
The Earth’s atmosphere bends light — rather like a giant prism. The effect is greater in the lower, denser layers of the atmosphere, so rays of light from the sun or moon are curved slightly downwards. Shorter wavelengths of light are bent more than longer wavelengths; therefore, green light from the sun or moon appears to be coming from a slightly higher position than the orange and red light, from an observer’s point of view. When the conditions are just right — with an additional mirage effect due to the temperature gradient in the atmosphere — the elusive green flash is briefly visible at the upper edge of the solar or lunar disc when it is close to the horizon.
Summary: ESO Photo Ambassador Gerhard Hüdepohl, who works at the Paranal Observatory in Chile, has captured what may be the best image ever taken of a green flash visible from Earth, as seen on the edge of the moon.
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