May 30, 2020
You are a way for the cosmos to know itself, Carl Sagan once said. On your birthday, the cosmos got to know itself a little better.
Green Flashes: Sun, Moon, Venus, Mercury
Birthday · May 30, 2020
A little universe, just for you
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APOD published May 30, 2020. Credit: Marcella Giulia Pace. A publication-date match, not a photo taken on your date. Independent of NASA.
Follow a sunset on a clear day against a distant horizon and you might glimpse green just as the Sun disappears from view. The green flash is caused by refraction of light rays traveling to the eye over a long path through the atmosphere. Shorter wavelengths refract more strongly than longer redder wavelengths and the separation of colors lends a green hue to the last visible vestige of the solar disk. It's harder to see a green flash from the Moon, not to mention the diminutive disks of Venus and Mercury. But a telescope or telephoto lens and camera can help catch this tantalizing result of atmospheric refraction when the celestial bodies are near the horizon. From Sicily, the top panels were recorded on March 18, 2019 for the Sun and May 8, 2020 for the Moon. Also from the Mediterranean island, the bottom panels were shot during the twilight apparition of Venus and Mercury near the western horizon on May 24.
Image credit: Marcella Giulia Pace