APOD: Lunar Farside (2011 Apr 09)

[emc]

I love the Moon. Our closest cosmic neighbor… not difficult to spot amongst the myriad of lights in the night sky… it’s a privilege to see such a clear view of the far side.

[deathbed rider]

I wonder what made the moon to lock one side to the Earth

[Chris Peterson]

I wonder what made the moon to lock one side to the Earth

Tidal locking, which eventually forces all orbiting rigid bodies to do this.

[bystander]

The FACT that no hues are applied, that scale is all stretched out past the boundaries of depth perception MEANS THIS PHOTO'S processing was never completed so anybody could see anything.

But what else is new? NASA doesn't expect to see anything, so they don't.

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'Brand-New' Moon Shines in NASA's Best Lunar Map Yet
Space.com | Science & Astronomy | Mike Wall | 2011 Apr 06

LOLA data from NASA's Lunar Reconnaissance Orbiter (LRO) shows three complementary views of the near side of the moon: the topography (left) along with new maps of the surface slope values (middle) and the roughness of the topography (right). All three views are centered on the relatively young impact crater Tycho, with the Orientale basin on the left side.

Credit: NASA/LRO/LOLA Science Team

[Brol2]

Hello,
I have often been puzzled by the fact that some pictures of a cratered surface sometimes give the impression that you see a kind of swellings, like blisters, instead of craters. Than, when you return the picture upside down, everything becomes all right: you see the craters. I invited several persons to look at the same images, and they generally have the same impression.
Now this picture of the moon's farside adds to the enigma: the left half looks like cratered, the right half like blistered! But then, if you flip the image around an horizontal axis, the left side becomes blistered, and the right cratered. And still more intriguine: if you rotate the image anti-clockwise, the lower half (ex-left) remains cratered, until... you look at the upper half and see it cratered also, and then look back at the lower half, which by then has become blistered !!? Finally, I looked from farther away, and was able to see the whole surface cratered... Is there any explanation of these optical effects?

[neufer]

I have often been puzzled by the fact that some pictures of a cratered surface sometimes give the impression that you see a kind of swellings, like blisters, instead of craters. Than, when you return the picture upside down, everything becomes all right: you see the craters. I invited several persons to look at the same images, and they generally have the same impression.
Now this picture of the moon's farside adds to the enigma: the left half looks like cratered, the right half like blistered! But then, if you flip the image around an horizontal axis, the left side becomes blistered, and the right cratered. And still more intriguine: if you rotate the image anti-clockwise, the lower half (ex-left) remains cratered, until... you look at the upper half and see it cratered also, and then look back at the lower half, which by then has become blistered !!? Finally, I looked from farther away, and was able to see the whole surface cratered... Is there any explanation of these optical effects?

One normally expects light sources to come from above and it is confusing when a light source comes from some other direction...especially from below (e.g., making a scary face with a flashlight from below). Typical telescopic photographs of a cratered quarter Moon have the lighting come from either the right or left and the mind can usually adjust in these simple nominal cases. However, the APOD confusingly simulates two quarter Moon shots that are artificially stitched together. Since the most prominent craters near the center just happen to be on the left side (with its simulated lighting from the left) your mind tries to assume that all the lighting is coming from the left (which is wrong for the right side). Hence, your mind makes mounds out of the craters on the right.

[Star*Hopper]

Is it just me, or does anyone else see a huge 'X' across the face?
And not as broad or prominent, but a vertical line as well, making it into an asterisk?

Ahh, you have discovered our logo, not yet complete. It's a part of our awareness program to generate interest
in the forum. Once it's complete, we plan to turn the Moon around so that what was the farside is facing Earth.

Well, you at least did 'catch' it.
Actually, I kinda suspected somethin' of the sort. A bit surprised, I might add, no 'Under Construction' signage was apparent
[Neuf slipping in his old age, or was he not privileged?]....but then on the other hand....'APOD propriety' & all that rot....

Carpe Noctem .... et tibi est!
~S*H

[NoelC]

if you ... left side becomes...

Perhaps you should have worded it "If I...", as not all of us see what you're describing.

Perhaps its my familiarity with viewing the moon, with working on astroimages, or just different coffee, but I don't see anything but craters in any orientation.

I don't doubt that you're perceiving what you say.

Understanding that people have different perceptions is part of being a successful artist.

-Noel

[RJGjr]

I wonder at times if the moon isn't just there to light up the night, but to protect us too! It seems evident by the blasting the darkside* has taken.

* Yes as in the Pink Floyd masterpiece, the "farside" is a comic strip!

[Star*Hopper]

"Yes as in the Pink Floyd masterpiece, the "farside" is a comic strip!"

Now there's ya some dark humour!
~S*H

[neufer]

Farcide = Farce + cide
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Farce, v. t. [F. Farcir, L. farcire; akin to Gr. to fence in, stop up. Cf. Force to stuff.]

1. To stuff with forcemeat; hence, to fill with mingled ingredients; to fill full; to stuff.
................................................
Farce, n. [F. farce, from L. farsus. See Farce, v. t.]

1. (Cookery) Stuffing, or mixture of viands, like that used on dressing a fowl; forcemeat.

2. A dramatic composition, originally exhibited by charlatans or buffoons, in the open street, for the amusement of the crowd, but now introduced upon the stage (& internet). It is written without regularity, and filled with ludicrous conceits. The dialogue is usually low, the persons of inferior rank, and the fable or action trivial or ridiculous.
................................................
sui-cide, n. [L. sui of one's self + caedere to slay, to kill.]
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[StarCuriousAero]

Seems odd to refer to it as the "farside" rather than the "darkside" of the moon a la Pink Floyd's 1972 masterpiece.

Darkside refers to the half of the moon that is not illuminated by the sun, not to the farside.

In other words, the dark side of the moon is simply the side opposite the sun, which to the earth observer is known as a new moon. The far side is only the dark side when we have a full moon.

[neufer]

In other words, the dark side of the moon is simply the side opposite the sun, which to the earth observer is known as a new moon.
The far side is only the dark side when we have a full moon.

It sort of depends on your definition of "dark."
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Dark, a. [OE. dark, derk, deork, AS. dearc, deorc; cf. Gael. & Ir. dorch, dorcha, dark, black, dusky.]

1. Not receiving, reflecting, or radiating light.

2. Not clear to the understanding; not easily through; obscure; mysterious; hidden.
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Of course:

1. The near side is never really "dark" when we have a new moon because it has a full earth.

2. And the far side is no longer obscure; mysterious; hidden.

<<There are two different meanings for the phrase “the dark side of the moon.” In the technical sense, astronomers use it to refer to the side of the moon which is not illuminated by the sun. The location of the dark side of the moon changes depending on where the moon is in its orbit. The confusion between the dark side of the moon and the far side of the moon is common. Many people use the term poetically to describe extreme isolation, in which case “dark” tends to scan better than “far.” Astronomers greatly appreciate it when people use the terms correctly, since they do in fact refer to different things.>>

[Withany]

The craters/dimples problem seems to me to be an artifact of NASA's processing. Exactly one half (the right side) of the image is somehow inverted. When the image is enlarged, you can see that in some caes, half (or at least a portion) of a crater is visually inverted, so that one the left side of teh half-way line, the crater appears, well, like a crater, while on the other side of the line, the crater appears like a dome. Perhaps whoever did the processing of the imagry flipped the switch the wrong way and inverted the right hand half of the image. I rather hope that NASA clears it up and provides a new, correct version for what is a very impressive image. And it would be nice if APOD posts the new one rather than merely going in and replacing the older, defective image in its archives.

[NoelC]

Exactly one half (the right side) of the image is somehow inverted.

It's interesting that you perceive it that way. It's just lit from the opposite direction.

-Noel

[Imagineer]

If I'm not mistaken, various seismometers have been placed on the Moon over time. Assuming such devices are operable and sensitive enough, is it possible to analyze such seismic readings in order to substantiate the theory that the far side crust is thicker? Would the LCROSS impact at the South Pole on 9-Oct-09 be useful? Even if such data exist to confirm the relative thickness of the near and far side lunar crust, they may not be sufficient to explain why.

[neufer]

If I'm not mistaken, various seismometers have been placed on the Moon over time. Assuming such devices are operable and sensitive enough, is it possible to analyze such seismic readings in order to substantiate the theory that the far side crust is thicker? Would the LCROSS impact at the South Pole on 9-Oct-09 be useful? Even if such data exist to confirm the relative thickness of the near and far side lunar crust, they may not be sufficient to explain why.

NASA Science News: Moonquakes

Buzz Aldrin deploys a seismometer.


Lunar seismograms from Apollo 16 station.

<<Between 1969 and 1972, Apollo astronauts placed seismometers at their landing sites around the moon. The Apollo 12, 14, 15, and 16 instruments faithfully radioed data back to Earth until they were switched off in 1977.

March 15, 2006: "NASA astronauts are going back to the moon and when they get there they may need quake-proof housing. Any habitat would have to be built of materials that are somewhat flexible," so no air-leaking cracks would develop. "We'd also need to know the fatigue threshold of building materials," that is, how much repeated bending and shaking they could withstand.

That's the surprising conclusion of Clive R. Neal, associate professor of civil engineering and geological sciences at the University of Notre Dame after he and a team of 15 other planetary scientists reexamined Apollo data from the 1970s. "The moon is seismically active," he told a gathering of scientists at NASA's Lunar Exploration Analysis Group (LEAG) meeting in League City, Texas, last October.

There are at least four different kinds of moonquakes:

• (1) deep moonquakes about 700 km below the surface, probably caused by tides;
  (2) vibrations from the impact of meteorites;
  (3) thermal quakes caused by the expansion of the frigid crust when first illuminated by the morning sun after two weeks of deep-freeze lunar night; and
  (4) shallow moonquakes only 20 or 30 kilometers below the surface.

The first three were generally mild and harmless. Shallow moonquakes on the other hand were doozies. Between 1972 and 1977, the Apollo seismic network saw twenty-eight of them; a few "registered up to 5.5 on the Richter scale," says Neal. A magnitude 5 quake on Earth is energetic enough to move heavy furniture and crack plaster. Furthermore, shallow moonquakes lasted a remarkably long time. Once they got going, all continued more than 10 minutes. "The moon was ringing like a bell," Neal says.

On Earth, vibrations from quakes usually die away in only half a minute. The reason has to do with chemical weathering, Neal explains: "Water weakens stone, expanding the structure of different minerals. When energy propagates across such a compressible structure, it acts like a foam sponge—it deadens the vibrations." Even the biggest earthquakes stop shaking in less than 2 minutes.

The moon, however, is dry, cool and mostly rigid, like a chunk of stone or iron. So moonquakes set it vibrating like a tuning fork. Even if a moonquake isn't intense, "it just keeps going and going," Neal says. And for a lunar habitat, that persistence could be more significant than a moonquake's magnitude.

What causes the shallow moonquakes? And where do they occur? "We're not sure," he says. "The Apollo seismometers were all in one relatively small region on the front side of the moon, so we can't pinpoint [the exact locations of these quakes]." He and his colleagues do have some good ideas, among them being the rims of large and relatively young craters that may occasionally slump. "We're especially ignorant of the lunar poles," Neal continues. That's important, because one candidate location for a lunar base is on a permanently sunlit region on the rim of Shackleton Crater at the Moon's south pole.

Neal and his colleagues are developing a proposal to deploy a network of 10 to 12 seismometers around the entire moon, to gather data for at least three to five years. This kind of work is necessary, Neal believes, to find the safest spots for permanent lunar bases. And that's just the beginning, he says. Other planets may be shaking, too: "The moon is a technology test bed for establishing such networks on Mars and beyond."

[JohnD]

Imagineer,
The Apollo seismometer network is still providing data:
Quote "two impacts clearly identified as far side highland sites possess a considerably thicker crust of 55–60 km."
http://w3admin.ipgp.jussieu.fr/docs/rec ... al2006.pdf
H. Chenet, Ph. Lognonné, M. Wieczorek, H. Mizutani. Lateral variations of lunar crustal thickness from the Apollo seismic data set. Earth and Planetary Science Letters 243 (2006)

John

[neufer]

A small, fresh crater on the lunar farside found in a MoonZoo survey by user JFincannon. Latitude: 34.2 Longitude: 228.25 between farside craters Charlier & Kovalevskaya. Credit: NASA / GSFC / ASU

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The Planetary Society Blog: Lovely crater turns up in MoonZoo
By Emily Lakdawalla | Apr. 18, 2011

<<Here's a very pretty picture to start off the week: a really gorgeous fresh crater on the lunar farside. There's nothing particularly unusual about this crater; it's just recent and fresh so there's a mesmerizing amount of detail in the feathery patterns of the ejecta that fans outward from it. This crater was turned up by a citizen scientist participating in the MoonZoo project, in which users are asked to trawl through the vast Lunar Reconnaissance Orbiter image data set to mark and classify small craters and other interesting features. Lunar Reconnaissance Orbiter should map nearly all of the Moon at a scale so much finer than any previous mission has managed, so it's revealing lovely features that were previously invsible, and turning up new detail in unappreciated spots, like this one.>>

[Star*Hopper]

Very interesting info there, Neufer....provides insights I've wondered about from time to time. Thanks for posting it!
~S*H

[Imagineer]

Thank you Art Neuendorffer and JohnD for your replies and helpful references.