2023-12-18 21:44:16
“What if we were wrong? What if the Earth was the Moon and the Moon was the Earth?”
The previous reflection is a gregería by Don Ramón Gómez de la Serna. Thus, if we looked at the “sky” from the Moon, we would get more than one surprise, starting with the majestic view of our planet.
But if a lunatic poet sang to eyes as blue as the sky, he would be a fraud… Because on the Moon he would not have found that blue inspiration that the sky offers us here.
These blue days. And red. And grey.
But what do we call heaven?
In colloquial terms, we refer to that vault that sheds an intense blue on us, which transmits optimism and which we associate with happy moments. Paradise Lost by Antonio Machado, who wrote that about “These blue days and this childhood sun…”.
But it’s not always blue. The Granada modernist Isaac Muñoz He described a sky red “like the blood of a God.”
And what happens on cloudy days? The sky looks white. Or grey.
And at night? Black. Or with red reflections if there are clouds and if the night is not too deep.
But that color palette that artists have reflected since prehistory has no place on our satellite.
Dawn on the Moon
astronauts on the mission NASA’s Artemis will set foot on the Moon again. If they stayed there long enough to see a sunrise (28 days, no less), they would miss that fire that on Earth compensates for early mornings.
From the Moon, as the Sun ascends, the only thing that differentiates it from other stars is its size and its blinding luminosity. Its light will be a white that is nothing like the yellowish one we see from Earth.
The bluish, whitish, grayish dome or combination of all of the above that the sky gives us on Earth does not exist on the Moon. Except for some optical effect if we take photographs, beyond the solar disk everything will be darkness speckled with stars as we move our view away from the Sun.
The Sun from the lunar surface. Image taken by the Apollo 12 mission in November 1969.
NASA, CC BY
Too small to have sky
Why don’t we see a colorful sky from the Moon?
The answer is simple: because it has no atmosphere. And why doesn’t it have an atmosphere? Because its mass is small and its weak gravitational force could not retain or attract gases after its traumatic separation from our planet. Without atmosphere there is no celestial vault, in the same way that without whys science does not progress.
In reality, the fact that the sky presents one color or another in different circumstances is due to two fundamental facts: the light of the Sun is composed of radiation of different colors (some invisible to us), and smaller atmospheric molecules and particles do not reflect them. They treat everyone equally. These particles scatter the blue lights in all directions as if from a game of pinball it was about. That game of pinball between air and blue light is called spreading. Blue light seems to come from everywhere in a cloudless sky.
When the Sun is low and its rays have to pass through a greater thickness of air, the spread of blue light is so high that the rays that reach us are almost exclusively red.
If there are many clouds, the sky looks white because the water droplets they contain disperse all the light equally without overshadowing the blue.
The master touch of our eyes
To the above we must add that our visual system perceives some colors better than others and that our brain deceives us: “it makes a pack” and assigns a single color to the lights we see, even if they are the sum of many. The final color that we perceive, although the purple is spread more, is blue.
On the Moon you cannot see a celestial vault because it does not have an atmosphere with particles, nor raindrops, nor clouds that play with the light to bathe us with the color that best suits it on each occasion.
And if there were a sea on the Moon, would it also be black like that sky that is not a sky? Well no.
If there were seas on the Moon like those on Earth, they would have color during the day. Impossible! You may think. But the sea is blue because it reflects the sky! The Greeks said it, they were never wrong, right? Well, they were wrong about that, although we forgive them for the beauty of the explanation.
What color would the lunar seas be? No one will be able to verify it, but here is my hypothesis: the water surface that received direct sunlight would have a strong bluish or whitish reflection and its surroundings would have a bluish tone that would fade as its angle with the solar disk increased.
In the words of Gómez de la Serna: “The sea likes impunity, and that is why it erases every trace on the beach.” And also the color of it.
#Moon #sky