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.

2024 March 11
Several images of a full moon setting are superposed.
The moon images are nearly white near the top, but turn
orange and then are covered by low clouds near the horizon.
Unusually, the setting moon images line up almost vertically.
In the foreground is a beach with waves illuminated by
blue-glowing plankton.
Please see the explanation for more detailed information.

A Full Plankton Moon
Credit & Copyright: Petr Horálek / Institute of Physics in Opava

Explanation: What glows in the night? This night featured a combination of usual and unusual glows. Perhaps the most usual glow was from the Moon, a potentially familiar object. The full Moon's nearly vertical descent results from the observer being near Earth's equator. As the Moon sets, air and aerosols in Earth's atmosphere preferentially scatter out blue light, making the Sun-reflecting satellite appear reddish when near the horizon. Perhaps the most unusual glow was from the bioluminescent plankton, likely less familiar objects. These microscopic creatures glow blue, it is thought, primarily to surprise and deter predators. In this case, the glow was caused primarily by plankton-containing waves crashing onto the beach. The image was taken on Soneva Fushi Island, Maldives just over one month ago.

Your Sky Surprise: What picture did APOD feature on your birthday? (post 1995)
Tomorrow's picture: horizon spiral


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