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Astronomy Picture of the Day

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

A distant sunset is seen between an orange sky and dark clouds. A close look at the Sun shows it is topped with several green strips, each known as a green flash. Please see the explanation for more detailed information.

A Multiple Green Flash Sunset

Explanation: Yes, but can your green flash do this? A green flash at sunset is a rare event that many Sun watchers pride themselves on having seen. Once thought to be a myth , a green flash is now understood to occur when the Earth's atmosphere acts like both a prism and a lens. Different atmospheric layers create altitude-variable refraction that takes light from the top of the Sun and disperses its colors, creates two images, and magnifies it in just the right way to make a thin sliver appear green just before it disappears. Pictured , though, is an even more unusual sunset. From the high-altitude Cerro Tololo Inter-American Observatory in Chile one day last April, the Sun was captured setting beyond an atmosphere with multiple distinct thermal layers, creating several mock images of the Sun . This time and from this location, many of those layers produced a green flash simultaneously. Just seconds after this multiple-green-flash event was caught by two well-surprised astrophotographers , the Sun set below the clouds.

Date March 28, 2023
Credit Image Credit & Copyright: T. Slovinský & P. Horálek ( IoP Opava ); CTIO , NOIRLab , NSF , AURA
Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (UMCP)
A service of: ASD at NASA / GSFC,
NASA Science Activation & Michigan Tech. U.