How did they know there was a 'dark side of the moon'?
In Disney's Mulan, Shang sings "I'll Make a Man Out of You" during the training montage, in which are the lyrics:
[You must be] mysterious as the dark side of the moon.
How did he know that there was a dark (far) side of the moon that never faced towards the earth? Or was he merely referring to the part of the moon without sunlight reflecting off it?
Best Answer
Making it into an answer as @Steve-O suggested.
It is possible that they already know that there is a Dark Side to the moon since they always see the same side. That is why they consider the Dark Side mysterious. They never saw it. China already have, AFAIK, a good knowledge of astronomy.
China, way before the Mulan story events, already had deep knowledge and were able to predict eclipses. In 120AD they were already able to tell that how the moon phases worked, so it was only a matter of noticing that there is another side to what they always see.
The sun is like fire and the moon like water. The fire gives out light and the water reflects it. Thus the moon's brightness is produced from the radiance of the sun, and the moon's darkness (pho) is due to (the light of) the sun being obstructed (pi). The side which faces the sun is fully lit, and the side which is away from it is dark. The planets (as well as the moon) have the nature of water and reflect light. The light pouring forth from the sun (tang jih chih chhung kuang) does not always reach the moon owing to the obstruction (pi) of the earth itself—this is called 'an-hsü', a lunar eclipse. When (a similar effect) happens with a planet (we call it) an occulation (hsing wei); when the moon passes across (kuo) (the sun's path) then there is a solar eclipse (shih).
Source: Chinese Astronomy
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How did we see the dark side of the Moon?
The US Lunar Orbiter programme then undertook the first detailed mapping of the far side of the Moon, but it was not until 1968 that the far side was first seen directly by human eyes, on the Apollo 8 mission.Is there an actual dark side of the Moon?
We always see the same side of the moon from Earth At the bottom right corner, the animation also tracks the boundary of sunlight falling across the moon as it rotates. So, half of the moon is in darkness at any given time. It's just that the darkness is always moving. There is no permanently dark side.Is the dark side of the Moon ever lit up?
The phenomenon of the Moon's darkened side being lit-up only happens in the last and first few days of the Moon's orbit of Earth.Nobody's Gonna Know... They're Gonna Know TikTok Compilation | How Would They Know?
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Answer 2
Obviously, it's just a song lyric, but it's not indefensible.
The dark side of the moon is not called "dark" because anyone thought it literally lacked sunlight. "Dark" in this expression means mysterious and unknown, as in "darkest Africa" -- somewhere where the light of understanding does not shine.
Chinese astronomers by the 5th Century AD certainly understood that the Moon was a spherical object phase-locked to the Earth, and therefore had a side that would never be visible from here. Whatever they called it could be translated as "the dark side of the Moon".
There is another question about whether a low-ranking army officer would have used that phrase when talking to (or singing to) a group of recruits, but hey, it's a movie.
"There is no dark side of the Moon. It's all dark."
-- Roger Waters
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