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Earth's Libration Visualized For the First Time Above the Moon's Far Side
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.
I thought that was moonshine liberating me.
It baffles be
perfect grammar
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.
What, you don't like exclamation points?!!!!!! What did you expect from Medium.com?!!!!!!!!
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."
Or to rephrase, it's not "it's", it's "its".
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
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.
I would much prefer that we record, rather than have to simulate effects like this.
He's got a cold.
"Wait. Something's happening. It's opening up! My God, it's full of apricots!"
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.
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:
Near Side "Moon Liberation" instructions are similar:
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.