What’s on the dark side of the moon?

What’s on the Dark Side of the Moon?NASAThere's a side of the moon that we don't get to see from Earth

  • China has launched the first mission to land a robotic craft on the far side of the Moon, Chinese media say.
  • The Chang'e-4 mission will see a static lander and rover touch down in Von Kármán crater, located on the side of the Moon which never faces Earth.
  • It blasted off from Xichang Satellite Launch Center on Saturday.
  • No space probe has ever reached that part of the moon's surface because of communication difficulties.

What’s on the Dark Side of the Moon?CNSAArtwork: The Chang'e-4 rover will explore a huge area on the far side of the moon

But in May this year China launched a satellite called Queqiao, or Magpie Bridge, to try and solve this problem.

The satellite will relay signals from the Chang'e-4 space probe on the far side of the moon back to scientists on Earth.

What is the 'dark side' of the moon?

  1. There's a part of the moon that we don't see from Earth as the moon always keeps the same side facing towards us.

  2. That side isn't actually always 'dark' but because not much is known about it, it's seen as a bit mysterious and that's why the name 'dark' is given.
  3. But a better name that is often used is the 'far side' of the moon.

What’s on the Dark Side of the Moon?NSSDCThis is one of the first pictures of the far side or 'dark' side of the moon.

In 1968, astronauts aboard the Apollo 8 spacecraft were the first humans to set eyes on the far side in person as they orbited the moon.

A few years earlier in 1959, the Luna 3 spacecraft returned the first pictures of the far side of the moon.

The Dark Side of the Moon – The National Space Centre – The National Space Centre

What’s on the Dark Side of the Moon?

View from the far side of the Moon. Credit: Apollo 8, NASA

What’s on the Dark Side of the Moon?

Water ice and volatiles at the lunar south pole. Credit: ESA

What’s on the Dark Side of the Moon?

Yutu-2 as images from Chang'e-4. Credit: CNSA / CLEP

The next images of the Moon’s far side were not taken until six years later in 1965 by the Soviet probe Zond 3. This mission captured much higher resolution images, revealing large chains of craters and a hemisphere that looked very different than the near 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.

Chinese rover reveals what lurks under the dark side of the moon

  • China’s Chang’e 4 lunar lander and Yutu-2 rover have used radar to see beneath the surface of the moon and reveal its hidden secrets.
  • China made history by becoming the first country to land a spacecraft on the far side of the moon, and now new data published to Science Advances reveals what is lurking beneath its surface.
  • After landing on the eastern floor of the Van Kármán crater near the Moon’s south pole on 3 January last year, Chang’e 4 (CE-4) deployed its Yutu-2 rover, which uses lunar penetrating radar (LPR) to open a window to an unexplored world.
  • “The subsurface at the CE-4 landing site is much more transparent to radio waves, and this qualitative observation suggests a totally different geological context for the two landing sites,” said the study’s author, Li Chunlai of the National Astronomical Observatories of the Chinese Academy of Sciences.

Li and his team used the LPR to send radio signals 40 metres deep into the surface of the moon. Using the high frequency channel of 500 MHz, the researchers were able to see three times deeper than the previous Chang’e 3 mission.

What’s on the Dark Side of the Moon?

The subsurface stratigraphy seen by Yutu-2 radar on the far side of the moon. Image: CLEP/CRAS/NAOC

An ‘unprecedented’ look

What’s on the Dark Side of the Moon?

Su Yan, a corresponding author of the study, added: “Despite the good quality of the radar image along the rover route at the distance of about 106 metres, the complexity of the spatial distribution and shape of the radar features make identification of the geological structures and events that generated such features quite difficult.”

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To get a better picture, the researchers combined radar images with tomographic data and quantitative analysis of the subsurface. This showed that the layer beneath the surface is made of highly porous granular materials embedding boulders of different sizes.

First quarter moon on February 12

Image above – first quarter moon – via Suzanne Murphy in Wisconsin. View full-sized image.

On February 12, 2019, the moon is at or near its first quarter phase, which means the portion of the moon we see from Earth is 50 percent illuminated by sunshine and 50 percent engulfed in the moon’s own shadow. It means that – for all of Earth – the moon rises around midday and sets around midnight.

The illuminated side of the February 12 first quarter moon will be pointing right at the red planet Mars. With binoculars, Mars and Uranus can be seen to occupy a single field of view. See the chart below.

What’s on the Dark Side of the Moon?

On February 12, 2019, the lit side of the moon points right at Mars and Uranus. Despite the moonlit glare, binoculars may enable you to see the Mars/Uranus conjunction in a single binocular field.

Click here for a sky chart via Sky & Telescope, keeping in mind that Uranus will be dimmer than Mars and the star Omicron Piscium (not shown).

Fortunately, Uranus appears as a dim “star” quite close to Mars, whereas the star Omicron Piscium is noticeably farther distant from the red planet.

EarthSky lunar calendars are cool! They make great gifts. Order now.

For the whole Earth, the moon reaches its exact first quarter phase on February 12, 2019, at 22:26 UTC; translate UTC to your time. At U.S. time zones, that is 5:26 p.m. EDT, 4:26 p.m. CDT, 3:26 p.m. MDT, 2:26 p.m. PDT, 1:26 p.m. Alaskan Time and 12:26 p.m. Hawaiian Time.

It’s good to remember that half the moon is always illuminated in space. In other words, the moon has a day side and a night side, just as Earth does.

At first quarter moon, we’re seeing about equal portions of the moon’s day side and night sides.

Because a first quarter moon is a waxing moon, we’re bound to see more of its day side each evening for another week or so, culminating with full moon on February 19.

The part of the moon that isn’t in sunlight is often called the moon’s dark side. Just realize that all of the moon undergoes day and night, just as Earth does. Any given lunar location experiences night for about two weeks, followed by about two weeks of daylight. So there’s a permanent far side of the moon, but no permanent dark side.

The moon does rotate on its axis. But billions of years of Earth’s strong gravitational pull have slowed it down such that today the moon takes as long to rotate as it does to orbit once around Earth. Astronomers would say that the moon is tidally locked with Earth. For that reason, one side of the moon always faces Earth.

Incidentally, the moon’s gravitational effects on Earth are much smaller, but – given billions of years of time – the Earth will slow down and keep one face always toward the moon.

Bottom line: The moon reaches its exact first quarter phase on February 12, 2019, at 22:26 UTC; translate UTC to your time. For the whole Earth, a first quarter moon rises around midday and sets around midnight.

Read more: Year’s biggest full moon on February 19

What’s on the Dark Side of the Moon?

Chinese Probe Uncovers New Mystery on the Dark Side of the Moon

What’s on the Dark Side of the Moon?

China far side moon lander

(Image: © CLEP/CNSA)

The “dark” side of the moon isn't really darker than the “light” side of the moon. But that far side does appear to get colder at night.

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Earth's moon is tidally locked to the planet, meaning that the same side of the moon faces us at all times. But the moon is still spinning in order to constantly point one face at us, so it experiences days and nights from the varying sunlight. These periods are about two Earth-weeks long.

Data from the Apollo missions had already revealed that the moon's sunlit surface can climb to 260 degrees Fahrenheit (127 degrees Celsius) during the day, and drop to minus 280 F (minus 173 C) at night. But all of that data comes from the side of the moon that faces Earth. The new Chinese mission that landed on the “dark” (read: far) side of the moon on Jan.

3 has recorded even colder temperatures during the long lunar night.

The Chinese lander Chang'e 4 and its rover, Yutu 2 (Jade Rabbit 2), woke from dormant, power-saving modes at the end of January and beamed back data suggesting that temperatures there had plummeted to minus 310 F (minus 190 C), according to an Agence France-Presse report. [Photos from the Moon's Far Side]

The difference between Chang'e 4's reading and the Apollo missions' is “probably due to the difference in lunar soil composition between the two sides of the moon. We still need more careful analysis,” Zhang He, executive director of the Chang'e 4 probe project, told Xinhua.

In other words, something about the lunar dirt where Chang'e 4 sits is probably causing the soil to retain less heat overnight than the Apollo landing sites did. But researchers still aren't sure what that something is.

Chang'e 4 and Yutu 2 are the first probes to explore the far side of our nearest neighbor, so the data they return will be one of a kind. It may be a long time before researchers have a firm answer to the temperature-difference question.

Originally published on Live Science.

Exploring the Lunar Far Side

We've all heard the term “dark side of the Moon” as a description for the far side of our planet's satellite.

It's actually quite a mistaken idea based on a misconception that if we can't see the other side of the Moon, it must be dark.

It doesn't help that the idea crops up in popular music (the Dark Side of the Moon by Pink Floyd is one good example) and in poetry.

The far side of the Moon as seen and photographed by the Apollo 16 astronauts.
NASA 

In ancient times, people really did believe that one side of the Moon was always dark. Of course, we now know that the Moon orbits Earth, and they both orbit the Sun. The “dark” side is merely a trick of perspective.

The Apollo astronauts who went to the Moon saw the other side and actually basked in the sunlight there. As it turns out, different parts of the Moon are sunlit during different parts of each month, and not just one side.

This image shows the phases of the Moon and why they happen. The center ring shows the Moon as it orbits around the Earth, as seen from above the north pole. Sunlight illuminates half the Earth and half the moon at all times. But as the Moon orbits around the Earth, at some points in its orbit the sunlit part of the Moon can be seen from the Earth. At other points, we can only see the parts of the Moon that are in shadow. The outer ring shows what we see on the Earth during each corresponding part of the moon's orbit.
NASA

Its shape seems to change, which is what we call the phases of the Moon. Interestingly, “New Moon,” which is the time when the Sun and Moon are on the same side of Earth, is when the face we see from Earth actually IS dark and the far side is brightly lit by the Sun. So, calling the part that faces away from us as the “dark side” really IS a mistake. 

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So, what do we call that part of the Moon we don't see each month? The better term to use is the “far side.” It makes perfect sense since it is the side farthest away from us.

To understand, let's look more closely at its relationship to Earth.

The Moon orbits in such a way that one rotation takes just about the same length of time as it takes for it to orbit around Earth.

That is, the Moon spins on its own axis once during its orbit around our planet. That leaves one side is facing us during its orbit. The technical name for this spin-orbit lock is “tidal locking.”

Earth and the Moon as seen from a passing spacecraft.
NASA

Of course, there is literally a dark side of the Moon, but it's not always the same side. What is darkened depends on which phase of the Moon we see. During a new moon, the Moon lies between Earth and the Sun.

So, the side we normally see from here on Earth that's normally lit by the Sun is in its shadow. Only when the Moon is opposite from the Sun do we see that part of the surface lit up.

At that point, the far side is shadowed and is truly dark. 

The far side of the Moon was once mysterious and hidden. But that all changed when the first images of its cratered surface were sent back by the USSR's Luna 3 mission in 1959. 

Now that the Moon (including its far side) has been explored by humans and spacecraft from several countries since the mid-1960s, we know much more about it.

We know, for example, that the lunar far side is cratered, and has a few large basins (called maria), as well as mountains. One of the largest known craters in the solar system sits at its south pole, called the South Pole-Aitken Basin.

That area is also known to have water ice hidden away on permanently shadowed crater walls and in regions just below the surface.

A Clementine view of the south pole/Aitkin Basin region. This is where the Chang'e 4 lander from China landed.
 NASA

It turns out that a small sliver of the far side can be seen on Earth due to a phenomenon called libration in which the moon oscillates each month, revealing a tiny bit of the Moon we'd otherwise not see. Think of libration as a little side-to-side shake that the Moon experiences. It's not a lot, but enough to reveal a bit more of the lunar surface than we normally see from Earth.

The most recent exploration of the far side has been undertaken by the Chinese space agency and its Chang'e 4 spacecraft. It's a robotic mission with a rover to study the lunar surface. Ultimately, China is interested in sending humans to study the moon personally.

Because the far side is shielded from radio frequency interference from Earth, it's a perfect place to put radio telescopes and astronomers have long discussed the option of placing observatories there.

Other countries (including China) are talking about locating permanent colonies and bases there. In addition, space tourists could find themselves exploring all over the Moon, both near and far side.

Who knows? As we learn to live and work on all sides of the moon, maybe one day we'll find human colonies on the far side of the moon. 

  • The term “dark side of the Moon” is really a misnomer for the “far side”.
  • Each side of the Moon is dark for 14 earth days each month.
  • The far side of the Moon has been explored by the United States, Russia, and China.

Updated and edited by Carolyn Collins Petersen.

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