What is kinetic light?

It is called gray light or gray light to the weak illumination shown by the Moon in the not directly illuminated by sunlight. Thanks to the gray light, this part of the Moon can be seen with the naked eye from Earth, albeit faintly.

As we all know, the Moon does not emit its own light, it just reflects the light of the Sun. Gray light is also reflected light, but instead of being reflected directly from sunlight, it is the reflection of light from the Earth, light that the Earth reflects from the Sun.

Gray light is not only produced on the Moon, but also on any other satellite, planet or astronomical object that does not emit its own light. Thanks to the gray light, the Cassini spacecraft was able to image Saturn’s satellites when they were reflecting Saturn’s light and not direct sunlight.

The phenomenon can be seen most clearly a few days before and after the New Moon, when the Moon enters the crescent phase and the part of the Moon illuminated by the Sun is very small. Nowadays, almost the entire disk of the Earth pointing towards the Moon is illuminated by the Sun, it reflects this light to the Moon and the Moon reflects it back to the Earth.

Gray light is also produced on Earth that would be visible from space and whose effects we can experience on full moon nights.

If we move away from environments affected by urban lighting on nights with a full moon and clear skies, the sunlight that is reflected by the Moon towards Earth allows us to walk comfortably at night. Some of that light, in turn, would be reflected off the Earth and seen from space as gray light on the planet.

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Leonardo da Vinci already explained this phenomenon at the beginning of the 16th century when he realized that both the Earth and the Moon reflected the light of the Sun at the same time. Light is reflected by the Earth to the Moon and from the Moon back to the Earth.


On a crescent Moon, the dark part of the Moon’s near side is illuminated by indirect sunlight reflected from Earth. Drawing by Leonardo Da Vinci depicting the gray light of the Moon Gray light on Iapetus (Saturn’s satellite)

Gray light and the search for planets

Gray light and the detection of reflected light by planets orbiting stars is one of the main techniques used to search for extrasolar planets, for example in the mission NASA Earth Planet Finder (mission canceled in 2011), or the European Space Agency’s Darwin Project (cancelled in 2007).

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