You may have never heard of cinereal light, but if you like to enjoy the moon, you've probably seen it. The cinereous light is that faint glow that illuminates the dark side do Earth's natural satellite in the first nights of the Crescent phase and at the end of the waning phase.

For centuries astronomers searched for an explanation for this glow, but only in the XNUMXth century was the phenomenon explained by the genius Leonardo Da Vinci.

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Leonardo Da Vinci portrait attributed to Francesco Melzi
Portrait of Leonardo Da Vinci attributed to Francesco Melzi. Source: wikimedia.org

The Italian Leonardo da Vinci was, certainly, one of the greatest geniuses who ever went through this planet. In his 67 years of life (1452 – 1519), he distinguished himself as a mathematician, engineer, inventor, anatomist, painter, sculptor, architect, botanist, poet, musician and astronomer.

As an artist, he was one of the most important names in the Renaissance, author of works such as “Monalisa” and “The Last Supper”. He was someone way ahead of his time. Centuries in advance, he designed flying machines, like a prototype helicopter. He also designed battle tanks, a mechanical calculator, and idealized the use of solar energy. And as an astronomer, he helped to unravel an ancient astronomical enigma: the cinereal light.

Monalisa (left) and The Last Supper (right) two of Leonardo Da Vinci's most famous works
Monalisa (left) and The Last Supper (right) two of Leonardo Da Vinci's most famous works

It is impossible not to be enchanted by the beauty of the Moon in the nights close to its new phase, with that faint glow that completes its unlit side.

But for centuries, this glow has intrigued astronomers and philosophers, who searched in vain for an explanation for the phenomenon. Some suggested that the Moon had its own glow, a kind of fluorescence, while others said it was starlight.

Crescent Moon with Cinereous Light
Crescent moon with cinerea light. Photo: Marcelo Zurita

You can imagine the size of this challenge at a time when astronomy was done without telescopes, and most people didn't even know that the Earth orbited the Sun.

But with the domain he had in several areas of knowledge and the creativity that one of the greatest artists our world has ever had, Leonardo Da Vinci solved the problem.

In his book Codex Leicester, written around 1510, Da Vinci “traveled” to the moon and imagined what the night would be like there. He already knew that the Sun was the center of the Solar System and that the Moon functioned as a great reflector of sunlight. He imagined that, in the same way, the Earth must reflect a great amount of light from the Sun.

Pages from the Codex Leicester book, where Da Vinci explains cinematic light
Pages from the Codex Leicester book, where Da Vinci explains cinematic light. Reproduction: covecollective.org

Then, when the sun goes down, the moon darkens, but not completely, because there is still a source of light in the sky: the Earth. In the same way as the Full Moon illuminates the nights here, the cinereal light was nothing more than the light from the Sun reflected from the Earth illuminating the night on the Moon.

The intensity of the cinereous light varies depending on the cloud cover on our planet. Thus, its observation is an indirect way of measuring the amount of clouds that surround the Earth.

Furthermore, we can study the chemical properties of our atmosphere through spectral analysis of cinerean light, much the same way as we do today to look for indicators of life on exoplanets.

Cinereal light spectrum allows the study of the chemical characteristics of the Earth's atmosphere
Cinereal light spectrum allows the study of the chemical characteristics of the Earth's atmosphere. Graphic: ESO

Today, with our telescopes, cameras and all the technology developed over 500 years ago, we know that our own planet illuminates the lunar surface 50 times more than the Full Moon, producing this faint glow on the surface. But in the XNUMXth century, only Leonardo Da Vinci's creativity and genius could solve the enigma that has intrigued humanity for centuries.

In his honor, the cinereal light is also called “da vinci shine".

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