Tuesday , April 20 2021

What is the dark side of the Moon?



Our House Know-It-Alls responds
questions about interactions with technology.

Q: What is the "dark side" of the Moon?

A: The short answer? It's a wrong name. A bad sound name! But a wrong name. Assuming I'm not talking about Pink Floyd or the French mockup, people who say "the dark side of the moon" almost always refer to the moon far away lateral – which, despite being constantly directed to those on the planet, actually sees as much light as the sun as the side that heads to Earth.

Maybe you already knew that. But! Did you also know that the lateral strides of the moonlight moon are constantly looking into sight? Or that some lunar regions are in fact shrouded in permanent darkness?

To understand why, you first need to understand why a part of the Moon is always pointing to Earth. For those here on the ground, the natural satellite of our planet seems never to return. But it actually returns all the time – it just rotates on its axis and the loops around our planet at the same rate: once every 27 days or so. When a cosmic body revolves around its parent and its axis at the same speed, astronomers say it is "tidal blocked."

Our moon was not born this way. Astronomers believe that, like many natural satellites, their lives began at a very different rate. (In our moon, astronomers believe they once turned around its axis faster.) But, over time, gravity on our planet exerted a couple on the coasts of the lunar surface, forcing its rotation in sync with orbital period. This phenomenon is actually quite common: Many of Saturn's and Jupiter's satellites are late in their mother planet.

The tide lock is the reason why I had no idea what the distant month of the month looked like until 1959 when the Luna 3 Soviet space probe broke the first photos of the landscape crater loaded. I looked better from: In 1968, astronauts from NASA's Apollo 8 mission became the first to look at the month's moon. NASA's Lunar Reconnaissance Orbiter mapped the entire monthly surface in high resolution in 2009. And in the first few days of 2019, China became the first country to make a soft landing of a spacecraft and launch a rover on the ever hidden face of the Moon . Chang Chang's 4 lander and Jade Rabbit 2 rover will give mankind his thoughtful looks at this distant lunar landscape.

But the truth is: you do not need a space ship to take a look at the side of the moon. While you can only see about 50% of the lunar disc at a time, the bonus smashes on its surface are constantly revealing to some careful observers. In fact, over a monthly cycle, up to 59% of the surface of the moon becomes visible to skygazers on Earth – assuming they know what to look for.

Check out this record from NASA's Science Visualization Studio. It was made using satellite images captured by the Lunar Reconnaissance Orbiter. The phase changes that you know undoubtedly: as the moon's position varies with the sun and the Earth, the darkness envelops itself and moves away from the face that is stuck with our planet (as it retracts and revolves from girl). But this animation – which condenses two and a half moon cycles in a single gif of 13 seconds – illustrates something about the moon that you have not seen before: The moon … is spinning.

Astronomers call these oscillations and are caused by the orientation of the moon's axis and the elliptical shape of its orbit. The inclination of its axis to Earth makes the moon appear as if the planet is a slow and gentle swallow, allowing observers to take a quick look at the Northern and Southern poles. Also, the eccentricity of the moon's orbit gives the face a slight inclination, allowing those on Earth to look on the eastern and western edges while spinning back and forth, unlike the party parrot: in Slack. (Its irregular orbit also explains the apparent changes in size due to its varying distance from Earth.)

And the incline of the moon's axis produces another interesting phenomenon: lunar surface specks that are really, always dark:

NASA / GSFC / Arizona State University

The above image is a map of the south pole illumination of the moon. It's a picture of over 1,700 photos captured by the Lunar Reconnaissance Orbiter over a six-month period. The regions of the pole that did not see the light at that time seem black; those who see the constant light appear white; the gray regions saw something between them. As a point of reference, the black circle near the center of the image is Crater Shackleton, a 13-mile impact crater with a rim that casts a long and perpetual shadow on the inside.

All this means: "The dark part of the Moon" may not exist technically, but "the craters of the eternal darkness" – which seems even cooler – is certainly certain.


Robbie Gonzalez is a senior writer for the WIRED science office. His fascination with the moon is due to his childhood, when at the age of 4 he first looked at him through a telescope. (Still holding that telescope.)

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