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Earth's Libration Visualized For the First Time Above the Moon's Far Side

Posted by timothy on from the can-you-see-your-house-from-there dept.

StartsWithABang writes Thanks to the fact that the Moon is tidally locked, we can only see 50% of its surface on any given night. Over time, the fact that the Moon's orbit is elliptical, and that it moves faster at perigee and slower at apogee means that up to another 9% is visible over the course of many years. The observed "rocking" and growing/shrinking of the Moon over time is known as lunar libration, an incredibly interesting phenomenon. But now, for the first time, we've been able to visualize how the Earth appears to move as seen from above the far side of the Moon.

33 comments

  1. Rocking the moon... by __aaclcg7560 · · Score: 3, Funny

    I thought that was moonshine liberating me.

    1. Re:Rocking the moon... by ClickOnThis · · Score: 4, Funny

      I thought that was moonshine liberating me.

      No, that's libation, not libration.

      --
      If it weren't for deadlines, nothing would be late.
    2. Re:Rocking the moon... by __aaclcg7560 · · Score: 1

      I'm American. My French isn't that great. :P

    3. Re:Rocking the moon... by wooferhound · · Score: 1

      The Labia as seen from the moon . . .

      --
      We are Dead Stars looking back Up at the Sky
    4. Re:Rocking the moon... by DanielOom · · Score: 2

      Let's sport the Earth Libation Font!

  2. incredibly interesting phenomenon by swell · · Score: 0

    So, I wanted to poo poo this stupid phrase. But hey, it is interesting. RTFA.

    --
    ...omphaloskepsis often...
    1. Re:incredibly interesting phenomenon by arglebargle_xiv · · Score: 0

      Thanks to the fact that the Moon is tidally locked, we can only see 50% of it's surface on any given night.

      "No one quite knows where the moon came from, but it's as old as the Earth, or very nearly. And it's survived this long because it has the most perfect defence system ever evolved. It's Tidally Locked. It doesn't exist when it's being observed. The moment it's seen by any other living creature it freezes into rock. In the sight of any living thing, it literally turns into stone. And you can't kill a stone. Of course, a stone can't kill you either, but then you turn your head away. Then you blink. Then, oh yes, it can. And I'm sorry. I am very, very sorry. It's up to you now. Don't blink. Don't even blink. Blink and you're dead. It's fast. Faster than you can believe. Don't turn your back, don't look away, and DON'T blink. Good luck".

    2. Re:incredibly interesting phenomenon by RoverDaddy · · Score: 1

      I love Doctor Who, but I'm pretty sure you can kill a stone with a hammer and chisel, or a jackhammer if you're pressed for time, or with TNT if you're really in a hurry.

      --
      RETURN without GOSUB in line 1050
  3. Spelling Police by Anonymous Coward · · Score: 0

    It baffles be that an editor or a programmer cannot master basic English language spelling and grammar. How can I believe you about libration when you cannot muster the brains to know whether it's is possessive or not?

    we can only see 50% of it's surface

    1. Re:Spelling Police by gmagill · · Score: 2

      It baffles be

      perfect grammar

    2. Re:Spelling Police by Anonymous Coward · · Score: 0

      Well, you're 50% correct; you missed the other bit: we can see only 50% of its surface

    3. Re:Spelling Police by mrbester · · Score: 1

      He's got a cold.

      --
      "Wait. Something's happening. It's opening up! My God, it's full of apricots!"
  4. Science,much? by Anonymous Coward · · Score: 0

    we can only see 50% of it's surface on any given night

    So which nights can we see the other side? Oh, never.

    1. Re:Science,much? by osu-neko · · Score: 5, Informative

      we can only see 50% of it's surface on any given night

      So which nights can we see the other side? Oh, never.

      Actually, on any night other than the one precisely a lunar month from the given night, you can see some of that other side (the 50% you can't see tonight). That's what libration does -- expose some of that other 50% that you can't see tonight. Not all of it, sure, but some. You can only see 50% on any given night, but you can see 59% over time. Thus, 18% of tonight's "other side" will be "this side" on some other night.

      --
      "Convictions are more dangerous enemies of truth than lies."
    2. Re:Science,much? by jc42 · · Score: 1

      we can only see 50% of it's surface on any given night

      So which nights can we see the other side? Oh, never.

      Actually, on any night other than the one precisely a lunar month from the given night, you can see some of that other side (the 50% you can't see tonight). That's what libration does -- expose some of that other 50% that you can't see tonight. Not all of it, sure, but some. You can only see 50% on any given night, but you can see 59% over time. Thus, 18% of tonight's "other side" will be "this side" on some other night.

      We could get even pickier, and note that the question was about when we (i.e., all humans) can see (some part of) the other side. At any given instance, the moon is visible from close to 50% of the Earth, and from the moon's viewpoint, our planet is 2 degrees wide. So people along the great circle where the moon is on the horizon can all see about 1 degree to the side of someone standing in the middle of that great circle (perhaps on a boat at sea). If you do a bit of calculating, you'll find that, depending on just how far away the moon is at the time, those people on the Earth's limb (from the moon's viewpoint) can together see about 51% of the moon total. It probably helps if you do this at a new moon, of course, though the reflection off the Earth often helps illuminate the rest of the moon at times..

      But the libration is the big part of the over-50% of the moon that we can see over time, since it raises the coverage to around 59%.

      I'll leave to someone else the calculation of the effect the moon's not-quite-circular orbit has on these calculations. And I'm sure there are some astronomers lurking about that can give us the numbers to 3 or 4 decimal places. ;-)

      (Hmmm ... I wonder if we can find that on wikipedia? ...)

      --
      Those who do study history are doomed to stand helplessly by while everyone else repeats it.
    3. Re:Science,much? by Anonymous Coward · · Score: 0

      and from the moon's viewpoint, our planet is 2 degrees wide.

      With global warming, that will expand to 3 or 4 degrees over time.

  5. Early analog work from the 1960's by Cliff+Stoll · · Score: 5, Informative

    From 1964 through around 1975, planetary astronomers at Tucson's Lunar & Planetary Laboratory used physical models to project and remap the moon's surface. They took high resolution photos through an earth based telescope, and then projected the images onto a spherical, white plaster globe. By carefully controlling the geometry, and knowing distances, angles, and (yes) lunar libation, they created detailed maps of the moon's near side, taking into account geometric distortion around the limbs. In this way, they could rephotograph parts of the lunar far-side.

    The rectified lunar atlas can now be seen at https://www.lpl.arizona.edu/si...

    This was all done using telescopes, photographs, and optical projection ... all analog, earth-based work. (the main telescope was the 61" reflector at Mt. Bigelow in Tucson; the films were Kodak 3-AJ 10x10inch glass plates)

    It was my honor to work with several of these astronomers, including Ewen Whitaker, Gerard Kuiper, Bill Hartmann, and Bob Strom. Brilliant scientists who would be astounded and impressed to see those NASA/Goddard videos. What we take for granted today, once required several years of detailed work.

    1. Re:Early analog work from the 1960's by ganjadude · · Score: 1

      I was reading some works of hartmann just the other day! Hes one of my favorites. it must have been simply amazing getting to speak with him, let alone work with him

      --
      have you seen my sig? there are many others like it but none that are the same
    2. Re:Early analog work from the 1960's by JohnVanVliet · · Score: 1

      now we use software like "ISIS3" and "Stereo-pipeline" to map the LRO images
      and the naif spice kernels for orbits ( the earth and moon are in "de430.bsp" )
      this leads to being able to run that video in the SIM "Celestia"

      --
      "I don't pitch OpenSUSE Linux to my friends, i let Microsoft do it for me
    3. Re:Early analog work from the 1960's by JohnVanVliet · · Score: 1

      cel://SyncOrbit/Sol:Earth:Moon/2015-02-08T03:17:32.13587?x=X0B5XeUyV////////////w&y=5sD7HnFLAw&z=dSp0ZVL6Ag&ow=0.706925&ox=0.0083696&oy=0.707185&oz=0.00877295&select=Sol:Earth:Moon&fov=17.7562&ts=1000&ltd=0&p=0&rf=71079831&lm=6278&tsrc=0&ver=3

      --
      "I don't pitch OpenSUSE Linux to my friends, i let Microsoft do it for me
  6. yay for unreadable linkspam by Anonymous Coward · · Score: 0

    unreadable sites are always a nice addition, so persist, little serial poster, persist!

    1. Re:yay for unreadable linkspam by jeffb+(2.718) · · Score: 1

      What, you don't like exclamation points?!!!!!! What did you expect from Medium.com?!!!!!!!!

  7. Re:Grammar by Anonymous Coward · · Score: 1

    Or to rephrase, it's not "it's", it's "its".

  8. Nice but wish it was video from L2 by joe_frisch · · Score: 2

    I would much prefer that we record, rather than have to simulate effects like this.

    1. Re:Nice but wish it was video from L2 by Anonymous Coward · · Score: 0

      As long as we're making expensive wishes, I'll go one cheaper: I'd rather have a million bucks! Send the money to me, and I'll make more crappy simulation videos. Everybody wins! :D

      ...

      ... except joe_frisch. Sorry dude, can't win 'em all. Better luck next time.

    2. Re:Nice but wish it was video from L2 by itzly · · Score: 1

      What purpose would that serve, except burn a bunch of money ?

    3. Re:Nice but wish it was video from L2 by thegarbz · · Score: 1

      I'm sad to say THIS!

      I wish we were in a world where it would cost next to nothing to go out and look ourselves, but with detailed view of what the moon looks like and the good understanding we have of orbital mechanics, a mission like this would be of zero scientific value.

    4. Re:Nice but wish it was video from L2 by joe_frisch · · Score: 1

      I wasn't suggesting a mission just to measure this (which of course can be simulated), but rather that it would be something that could easily be recorded form one of the many existing missions(or maybe tourist hotels) that would be distributed throughout the solar system.

  9. "But now, for the first time, we've been able..." by wonkey_monkey · · Score: 1

    But now, for the first time, we've been able to visualize how the Earth appears to move as seen from above the far side of the Moon.

    We've been able to do this for decades. If this really is the first time - and I'm not inclined to take medium.com's* word on that - then it's more a case of "the first time someone could be bothered."

    * how many exclamation marks? Jesus.

    --
    systemd is Roko's Basilisk.
  10. Re:"But now, for the first time, we've been able.. by Howitzer86 · · Score: 1

    Correct. you can do this in Orbiter Space Flight Simulator by playing with the Camera settings and speeding up the time dilation.

    Far Side "Earth Liberation" Instructions:

    • - Hit F4 to bring up the Main Menu
    • - Click Camera
    • - Set Target to Moon
    • - Click Apply
    • - Hold Z to reduce the FoV down to the lowest degree, then pan out with the mouse wheel
    • - Make sure View Mode is set to "target-relative" (indication in the upper left) if not, hit F2 until it does
    • - Rotate your view around to the far side of the moon until you see the Earth.
    • - Speed up time dilation by hitting T

    Near Side "Moon Liberation" instructions are similar:

    • - Hit F4 to bring up the Main Menu
    • - Click Camera
    • - Set Target to Earth
    • - Click Apply
    • - Click Track
    • - Set Target to Moon (click Target to...)
    • - Scroll mouse wheel until the camera pans all the way into the Earth and you see the other side (you should see the moon)
    • - Make sure View Mode is set to "absolute-direction"
    • - Speed up time dilation by hitting T

    Their presentation is much better though, especially for the Moon Liberation because the FoV in Orbiter is limited to 10 degrees as a minimum. Saving your scenario and editing the file (it's all text files), might work around that.

    The simulator uses mathematical models that are true to life, I forget the names of them but they're well known models that are used to predict things like eclipses and planet locations in planetarium software.