Earth's Axis: What is Figure Axis & Have Astronomers Had to Readjust?

[curiouschris]

if the pole shifted even a small fraction of a degree, all astronomical telescopes would be unable to find or track their sources, and all GPS systems would cease to function.

Ha! that was exactly what my premise, and my original question. over and above that I figured without doing any math to prove it :( that such a sudden albeit small shift would cause massive disturbances in the ocean etc. Imagine the amount of energy required to get all the oceans in the world to shift 8cm in whatever direction within a 3 minute time scale.

So now my question moves on to. Why would any person of scientific bent not correct the error as soon as they realized what they said was misinterpreted?

I believe the initial quote was attributed to a NASA scientist but can't recall who. Not David Morrison I hope.

CC

 

[ViewsofMars]

Reports being aired in the press about the Earth's axis having moved.
CC

Hi curiouschris, I think it may pertain to the following fact. It's about paleoclimatology.

The Earth circles the Sun in a flat plane. It is as if the spinning Earth is also rolling around the edge of a giant, flat plate, with the Sun in the center. The shape of the Earth’s orbit—the plate—changes from a nearly perfect circle to an oval shape on a 100,000-year cycle (eccentricity). Also, if you drew a line from the plate up through the Earth’s North and South Poles—Earth’s axis—the line would not rise straight up from the plate. Instead the axis is tilted, and the angle of the tilt varies between 22 and 24 degrees every 41,000 years (obliquity). Finally, the Earth wobbles on its axis as it spins. Like the handle of a toy top that wobbles toward you and away from you as the toy winds down, the “handle” of the Earth, the axis, wobbles toward and away from the Sun over the span of 19,000 to 23,000 years (precession). These small variations in Earth-Sun geometry change how much sunlight each hemisphere receives during the Earth’s year-long trek around the Sun, where in the orbit (the time of year) the seasons occur, and how extreme the seasonal changes are.
http://earthobservatory.nasa.gov/Features/Paleoclimatology_Evidence/

Chris, you asked, "So now my question moves on to. Why would any person of scientific bent not correct the error as soon as they realized what they said was misinterpreted?"

My response to you is that you might be taking two separate issues and attempting to put them together. My prior contribution by David Morrison about astrobiology doesn't diminish the value paleoclimatology. They often work hand in hand together. Perhaps you can see now how that could be for you.


Chris, you mention, "I believe the initial quote was attributed to a NASA scientist but can't recall who. Not David Morrison I hope."

I honestly don't think any NASA scientist including David Morrison would deceive anyone. Chris, I hope you will understand that until you can provide me the quote in mention so I can examine it then I will have to dismiss it as being factual.

I'm glad that you are a curious person. I am too! Have a great day.

Mars

 

[curiouschris]

Hi ViewsofMars

I am fully aware of the Earth's eccentricity, I must admit I was surprised by the scale of Chandlers wobble. but the time scales are still significantly different.

Here is one article
http://www.businessweek.com/news/2010-03-01/chilean-quake-likely-shifted-earth-s-axis-nasa-scientist-says.html

It says the source was Richard Gross, a geophysicist at NASA’s Jet Propulsion Laboratory.

Deception is not a word I would use, although its not a strong enough word for some examples. East Anglia climate research unit springs hotly to mind, deception is too mild in that case, deliberate fraud would fit more appropriately.

My concern is most would realize the press like to sensationalise (another word for deceive I guess) and should frame responses most carefully. If it is apparent that the response was misworded or misquoted seek to correct that immediately.

It appears this does not happen often enough. Or as is often the case the media don't print a retraction, probably because its not sensational enough.

But I am cynical enough to realize that if money or notoriety is involved, the occasional misinterpretation would be allowed to stand uncorrected. To assume everybody in anyone field be it science, religion or politics is 100% honest is pure folly.

One problem I realized as this thread progressed was the different meanings of the same term. to me the word axis means the point (or shaft as per DH) about which something rotates. it appears others think of it differently, something that I would probably call the notional axis.
In the minds of the great unwashed, me included, to say the axis moved, means the tilt of the Earth changed and in this case the time frame was short, ~3 minutes I am led to believe.

CC

 

[D H]

Here is one article
http://www.businessweek.com/news/2010-03-01/chilean-quake-likely-shifted-earth-s-axis-nasa-scientist-says.html

From that article,

“The length of the day should have gotten shorter by 1.26 microseconds (millionths of a second),” Gross, said today in an e-mailed reply to questions. “The axis about which the Earth’s mass is balanced should have moved by 2.7 milliarcseconds (about 8 centimeters or 3 inches).”​

The article does not say the Earth moved. It says the Earth's axis moved. Big difference. Dr. Gross is not responsible for misreadings of his statement.

It says the source was Richard Gross, a geophysicist at NASA’s Jet Propulsion Laboratory.

Not just any geophysicist, a rather prominent one in the field of modeling and measuring Earth's rotation. From his CV: http://www.iag-ggos.org/sp/bios/Gross_cv.pdf

Professional Affiliations and Activities
Eos Corresponding Editor for Geodesy, 2003–present
President, IAG Subcommission 3.3 on Geophysical Fluids, 2003–present
Chair, IERS Special Bureau for the Oceans, 1998–present
Chair, IAG/IAPSO JWG on Geodetic Effects of Nontidal Oceanic Processes, 1999–2003
Member, IERS Working Group on Combination, 2003–present
Member, Joint IAU/IUGG Working Group on Non-Rigid Earth Nutation Theory, 1994–1999
Member, IAG Special Study Group 5.143 on Rapid Earth Orientation Variations, 1991–1995
Member, IAU WG on Earth Rotation in the HIPPARCUS Reference Frame, 1991–1997
Member, IAU Commission 19 (Rotation of the Earth), 1994–present
Member, IERS Special Bureau for the Mantle, 1998–present
Ex-officio member, IERS Special Bureau for Loading, 2002–present
Fellow, International Association of Geodesy (IAG), 2003–present
Member, American Geophysical Union, 1978–present
Member, European Geosciences Union, 2003–present
Member, European Geophysical Society, 2000–2002
Associate Member, International Earth Rotation and Reference Systems Service (IERS)
Co-organizer of Workshop on Forcing of Polar Motion in the Chandler Frequency Band, 4/04
Session organizer and chair for AGU, EGS, EGU, IAG, and IUGG conferences
Manuscript reviewer for Science, Nature, JGR, GRL, GJI, J. Geodesy, J. Geodynamics, et al.
Proposal reviewer for NASA and US National Science Foundation
Member, GRACE Science Team, Ørsted Science Team; Lead-Co-Investigator of CHAMP​

One problem I realized as this thread progressed was the different meanings of the same term. to me the word axis means the point (or shaft as per DH) about which something rotates. it appears others think of it differently, something that I would probably call the notional axis.
In the minds of the great unwashed, me included, to say the axis moved, means the tilt of the Earth changed and in this case the time frame was short, ~3 minutes I am led to believe.

The Earth's rotation axis is the axis about which the Earth rotates. I used the term "shaft" because that is how I thought you were envisioning it, curiouschris.

The source of your misunderstanding is that you envisioned the Earth's rotation axis as having a fixed orientation in space. That simply is not the case. It is the Earth's angular momentum vector that remain essentially constant over shortish periods of time. The Earth's rotation axis is the direction in which the Earth's angular velocity vector is pointing. Any change in the Earth's moment of inertia means the angular velocity vector has to change accordingly because it is angular momentum that is a conserved quantity.

A part of the problem is that rotational dynamics is considerably more difficult concept than translational dynamics. Because linear momentum is the product of a scalar quantity (mass) and a vector (velocity), linear momentum and velocity always point in the same direction. In comparison, angular momentum is the product of a second order tensor quantity (the moment of inertia tensor) and a vector (angular velocity). Angular momentum and angular velocity only point in the same direction in simple freshman physics problems.Several lay articles on this subject use a figure skater as an analogy. I see a better analogy in the motion of an aerial ski jumper. An aerialist's angular momentum will be constant during the short period of time between takeoff and landing. Aerialist intentionally rotate their hips, move their arms, etc. during their short flight to change their angular velocity. A couple of videos on the physics of aerial skiing:

http://www.dailymotion.com/video/xc3oq6_aerial-skiing_sport

 

[curiouschris]

The Earth's rotation axis is the axis about which the Earth rotates. I used the term "shaft" because that is how I thought you were envisioning it, curiouschris.

Yes and its the source of the confusion. but not just for me. ask anyone outside of the forum in a poll and most people will answer the same as myself.
A common answer would be "the axis is the shaft about which the Earth rotates".

The source of your misunderstanding is that you envisioned the Earth's rotation axis as having a fixed orientation in space.

No I never misunderstood this.

You and every one else assumes I misunderstood it. I knew the Earth wobbled around its axis. Exactly the same as a child's top will wobble if it is unbalanced.

All the 'normal' divergences from the 'true axis' would be accounted for when calibrating equipment.
Therefore a sudden and unexpected change in the 'tilt' of the Earth as a result of the change in the position of the 'axis'(shaft) would result in the need to recalibrate telescopes, perhaps not ones looking at the moon mind you, that would still be relatively minor, but ones looking into deep space, whole galaxies would have disappeared from the view in a 3 minute period.

Because of this and the other reasons, and ones I hadn't considered like the GPS issue told me the statement by Richard Gross was patently false, as it was understood by me and the ones around me.

After a fair bit of research by myself and the others in my dept. (for curiosity reasons only). All people with above average intelligence, who all assumed the same meaning of the word axis by the way. We realized the 'principle axis' (as mentioned in other articles) meant a 'notional axis' and this was the axis that Mr Gross was discussing.

I posted my question here during that research period. I posted it in this forum (astronomy) to get a concise answer to my question. but I could have easily posted it in a different forum and just worded it different. my question was simple did any astronomer have to recalibrate their equipment.

If the answer was NO then the Earth's axis as understood by the majority did not move. and our suspicions to the misunderstanding are confirmed.

If the answer was YES then I had to seriously reconsider my understanding of the natural world. because to me such a thing was impossible without other serious side effects.

After a considerable amount of beating around the proverbial bush, we have arrived at the answer NO

Had Mr Gross worded his reply differently, changing

“The axis about which the Earth’s mass is balanced should have moved by 2.7 milliarcseconds (about 8 centimeters or 3 inches).”

to

“The point about which the Earth’s mass is balanced should have moved by 2.7 milliarcseconds (about 8 centimeters or 3 inches).”

Then none of the misunderstanding would have arisen.

CC

 

[russ_watters]

Ha! that was exactly what my premise, and my original question. over and above that I figured without doing any math to prove it :( that such a sudden albeit small shift would cause massive disturbances in the ocean etc. Imagine the amount of energy required to get all the oceans in the world to shift 8cm in whatever direction within a 3 minute time scale.

You did read that a 3' tsunami propagated across essentially the entirety of Earth's oceans, right?

So now my question moves on to. Why would any person of scientific bent not correct the error as soon as they realized what they said was misinterpreted?

It sounds to me like this isn't a matter of misinterpretation, it is that you think something that was correct was not correct. Ie, from the OP:

So my question is, "hey guys have you had to readjust your telescopes?"

Answer: No. Does that mean the article berkeman linked was wrong? No. The article presents two (claimed) facts. Both appear correct. You appear to believe the effects would be more noticeable than they are. You are not correct. The best earth-based telescopes have a resolution on the order of .05 arcsec, with software or adaptive optics to help counter atmospheric distortion. Thus a change of .0026 arcsec would not be noticeable.

 

[curiouschris]

Hmmm No I didn't hear about the 'tsunami' I heard the tsunami alert was sounded but it never eventuated. That's what I would have expected. and to be honest if I had heard that I probably would have said "oh sht the world did tilt on its axis".
But maybe not, I also thought that we should also note a blast of wind. I wouldn't have known how strong and that may have been ignored as a sudden puff of wind. so I didn't pursue that. I also considered large unfixed masses such as the arctic icecap. They would have tried to move in response so the motion of the earth, the result being a sloshing of the oceans. perhaps that may have resulted in significantly larger waves or perhaps not, I couldn't be sure.

Its a misinterpretation. no doubt about that. What he wrote in response to the question asked was factually correct. That doesn't mean there isn't room for misinterpretation. and as was stated, dealing with the press often means accidental or deliberate misinterpretation. sensationalist news "The Earth's axis has moved by 8cm" sells better than "the Earth's notional axis was displaced by 8cm, but no cause for alarm because its really only something used in the modeling of the Earth's position and rotation". truth be known it moves every time I go for a walk!

You are correct I assumed Earth's telescopes are more accurate than that. I believed looking into deep space even a slight change in Earth's position would change the section of the sky being viewed. This belief is supported by ViewsofMars comments attributed to David Morrison. but you are saying he is wrong or at least the statement "fraction of a degree" should have been worded more precisely.

If someone had responded to my original question with "No. Earths telescopes don't have enough resolution to be effected by such a small change". I would have accepted that as well.

CC

 

[Chronos]

Google on gravity probe B and see what you think.

 

[mgb_phys]

if the pole shifted even a small fraction of a degree, all astronomical telescopes would be unable to find or track their sources, and all GPS systems would cease to function

That's why I'm glad that the air force runs GPS not Nasa.

And he obviously isn't a radio astronomer, you can read the change in rotation of the Earth and even the shift in continents directly from the correlator in VLBI

 

[D H]

That's why I'm glad that the air force runs GPS not Nasa.

And he obviously isn't a radio astronomer, you can read the change in rotation of the Earth and even the shift in continents directly from the correlator in VLBI

Their is way too much misreading / overreading going on in this thread.

Morrison was debunking one of the myriad 2012 myths when he wrote "if the pole shifted even a small fraction of a degree, all astronomical telescopes would be unable to find or track their sources, and all GPS systems would cease to function." He obviously was talking about fractions of a degree in the lay sense of the word "fractions": 1/10, 1/20, maybe 1/100, but not 7.5×10^-7 degrees (2.7 milliarcseconds). Look at who he was writing to and the question that was being asked.

What Morrison wrote was correct. If the Earth's orientation changed by "fractions of a degree" and we did not know about it, our telescopes and GPS systems that require knowledge of the Earth's orientation to the sub-arcsecond level would cease functioning.

BTW, David Morrison has a PhD in astronomy and directed telescope arrays before moving on to bigger and better things.

 

[ViewsofMars]

Thanks for your patience. I spent my weekend at the beach. Freez'n cold but the waves were incrediable and the company divine.

Back on our current topic...I did a brief search and found this from NASA.

Chilean Quake May Have Shortened Earth Days
03.01.10
The Feb. 27 magnitude 8.8 earthquake in Chile may have shortened the length of each Earth day.

JPL research scientist Richard Gross computed how Earth's rotation should have changed as a result of the Feb. 27 quake. Using a complex model, he and fellow scientists came up with a preliminary calculation that the quake should have shortened the length of an Earth day by about 1.26 microseconds (a microsecond is one millionth of a second).

Perhaps more impressive is how much the quake shifted Earth's axis. Gross calculates the quake should have moved Earth's figure axis (the axis about which Earth's mass is balanced) by 2.7 milliarcseconds (about 8 centimeters, or 3 inches). Earth’s figure axis is not the same as its north-south axis; they are offset by about 10 meters (about 33 feet).

By comparison, Gross said the same model estimated the 2004 magnitude 9.1 Sumatran earthquake should have shortened the length of day by 6.8 microseconds and shifted Earth's axis by 2.32 milliarcseconds (about 7 centimeters, or 2.76 inches).

Gross said that even though the Chilean earthquake is much smaller than the Sumatran quake, it is predicted to have changed the position of the figure axis by a bit more for two reasons. First, unlike the 2004 Sumatran earthquake, which was located near the equator, the 2010 Chilean earthquake was located in Earth's mid-latitudes, which makes it more effective in shifting Earth's figure axis. Second, the fault responsible for the 2010 Chiliean earthquake dips into Earth at a slightly steeper angle than does the fault responsible for the 2004 Sumatran earthquake. This makes the Chile fault more effective in moving Earth's mass vertically and hence more effective in shifting Earth's figure axis.

Gross said the Chile predictions will likely change as data on the quake are further refined.


Alan Buis
818-354-0880
http://www.nasa.gov/topics/earth/features/earth-20100301.html

I hope this helps.

 

[mgb_phys]

I hope this helps.

So do i still have to adjust my clocks?

 

[russ_watters]

Hmmm No I didn't hear about the 'tsunami' I heard the tsunami alert was sounded but it never eventuated.

You didn't watch the tsunami reach Hawaii live on TV? It wasn't much of a tsunami, so it was pretty boring, but it did happen.

Also, from what I understand, the tsunami is what caused most of the deaths in Chile.

That's what I would have expected. and to be honest if I had heard that I probably would have said "oh sht the world did tilt on its axis".
But maybe not, I also thought that we should also note a blast of wind. I wouldn't have known how strong and that may have been ignored as a sudden puff of wind. so I didn't pursue that. I also considered large unfixed masses such as the arctic icecap. They would have tried to move in response so the motion of the earth, the result being a sloshing of the oceans. perhaps that may have resulted in significantly larger waves or perhaps not, I couldn't be sure.

A tsunami is generated when a piece of the Earth's crust moves by many feet, so when the whole Earth moves by a few inches, it wouldn't cause a big, coherent, localized wave.

You are correct I assumed Earth's telescopes are more accurate than that. I believed looking into deep space even a slight change in Earth's position would change the section of the sky being viewed. This belief is supported by ViewsofMars comments attributed to David Morrison. but you are saying he is wrong or at least the statement "fraction of a degree" should have been worded more precisely.

Yes - you reacted to a non-specific crackpot claim as if it applied here. You were mistaken...though we probably shouldn't have allowed that post to remain. I think ViewsofMars posted it for the irony and assume that he knew what DH said:

He obviously was talking about fractions of a degree in the lay sense of the word "fractions": 1/10, 1/20, maybe 1/100, but not 7.5×10-7 degrees (2.7 milliarcseconds). Look at who he was writing to and the question that was being asked.

That was obvious to me too...a complete pole flip would be a total of a 180 degree change, so obviously, it wouldn't just be miliarcseconds that we'd be looking for.

Anyway...

If someone had responded to my original question with "No. Earths telescopes don't have enough resolution to be effected by such a small change". I would have accepted that as well.

You got that in post 11, but maybe it wasn't clear enough.

 

[curiouschris]

You didn't watch the tsunami reach Hawaii live on TV? It wasn't much of a tsunami, so it was pretty boring, but it did happen.

A localised tsunami. but that's not a 5' tsunami that circled the globe. which is what you stated. If it did I didn't hear about that. Here in Australia the east coast was put on alert but later it was rescinded.

For most things you don't have to worry about microsecond variations.

You got that in post 11, but maybe it wasn't clear enough.

I guess the "for most things" threw me

A tsunami is generated when a piece of the Earth's crust moves by many feet, so when the whole Earth moves by a few inches, it wouldn't cause a big, coherent, localized wave.

A wave is caused when I kick the the water at the beach. so what.

But take the entire globe and shift it by just 8 cm and I can't see that it wouldn't cause a massive disruption. You can't just pick up an ocean and move it.

But the point is moot the Earth didn't move the the ocean wasn't unsettled the sky didn't fall and apparently Viewsofmars took the mickey out of me.


CC

 

[D H]

But take the entire globe and shift it by just 8 cm and I can't see that it wouldn't cause a massive disruption. You can't just pick up an ocean and move it.

Nobody, including the press article you cited, said that the Earth shifted by 8 cm. The Earth's rotation axis moved, not the Earth as a whole. This continued misperception on your part of what was claimed and what was reported is your biggest obstacle to understanding, CC. Get rid of that picture. You are thinking of the Earth as if it were a rigid body and as if its angular momentum and angular velocity vectors are collinear.

A plot of the polar motion for the two week interval around February 27: http://hpiers.obspm.fr/eop-pc/produ...onth2=3&day2=6&langue=1&SUBMIT=Submit+request

Note that Feb 27 exhibits slightly more motion than the surrounding days. That might or might not be a signature of the earthquake. These data are developed after-the-fact and involve some smoothing. If the earthquake did result in a slight shift in the Earth's axis, it is hiding somewhere in the 37.8 cm motion observed between Feb 25 and Mar 2.

 

[ViewsofMars]

[russ watters comment to curiouschris]

Also, from what I understand, the tsunami is what caused most of the deaths in Chile.
A tsunami is generated when a piece of the Earth's crust moves by many feet, so when the whole Earth moves by a few inches, it wouldn't cause a big, coherent, localized wave. Yes - you reacted to a non-specific crackpot claim as if it applied here. You were mistaken...though we probably shouldn't have allowed that post to remain. I think ViewsofMars posted it for the irony and assume that he knew what DH said: That was obvious to me too...a complete pole flip would be a total of a 180 degree change, so obviously, it wouldn't just be miliarcseconds that we'd be looking for.

Anyway...
You got that in post 11, but maybe it wasn't clear enough.

Hi Russ,

First off, I'm a hetrosexual woman. I'm getting very upset by men calling me a "he." This isn't the first time here on physics forums it has happened to me where I HAVE HAD TO CORRECT the person for mistaking my identity. My question is why is it continuing? The impression I'm beginning to think is that women don't usually partake in discussions about Astronomy, Cosmology, etc. I've posted here before with valuable information. Also, I'm here to say, "WOMEN are welcomed to participate!"

My second point is that everything I've posted was reflecting what I felt to be information pertainent to what has been going around the Internet on different forums and what has been presented in newspapers and Internet articles. It's been confusing for many people.

My last post (3 of 3) on the previous page reflects what was often omitted from on-line articles. "Gross calculates the quake should have moved Earth's figure axis (the axis about which Earth's mass is balanced) by 2.7 milliarcseconds (about 8 centimeters, or 3 inches). Earth’s figure axis is not the same as its north-south axis; they are offset by about 10 meters (about 33 feet)." Reports have been confusing for lack of mentioning "earth's figure axis." Instead article's have been written stating "earth's axis" without denoting it's not the north-south axis in mention. The lay person is confused for good reason. This is why I posted my first response on the previous page from David Morrison. Here is a snippet from it, "if the pole shifted even a small fraction of a degree, all astronomical telescopes would be unable to find or track their sources, and all GPS systems would cease to function." My second post was an merely an *example* for the confusion.

Thanks,
Mars

 

[D H]

The north-south axis is simply the line connecting the Earth's geographic north and south poles. This is not the Earth's rotation axis. Think about it this way: Just because the Earth's rotation axis moves by some amount (20 meters over the course of a year) does not mean that the extremely well-mapped latitude and longitude coordinates of a spot on the Earth need to change to suit. Were it not for continental drift, those well-mapped latitude/longitude coordinates would remain constant no matter what axis the Earth happens to be rotating about.

The north-south axis is what geographers thought was the Earth's figure axis (mean pole) at noon on January 1, 1903. The intersection between this axis and the Earth's surface are the north and south poles. The official name for the geographic North pole is the "Conventional International Origin" and was estimated via six International Latitude Observatories. (You can google those phrases). Our latitude/longitude system was frozen in 1903 with early 20th century tecnhnology.

The Earth's instantaneous rotation axis deviates from the CIO by a measurable amount by some period changes (435 day Chandler wobble and yearly variations) plus what appear to be a longer-term drift. A plot:

http://www.iers.org/SharedDocs/Bilder/EN/Polar__motion2001__2006__polhody,property=default.png

Another name for the figure axis is the mean pole. In other words, it is the location of the rotation axis after accounting for the quasi-periodic Chandler wobble and annual variations. Notice that the motion of the mean pole is considerably smaller in magnitude than is the motion of the instantaneous axis of rotation (polhody in the above plot). An 8cm shift might be observable after the fact. The difficulty lies is untangling all of known contributors to polar motion. The biggest are seasonal changes in the atmosphere and Chandler wobble, and both are a bit noisy.


A more recent release from NASA on this topic:
http://science.nasa.gov/headlines/y2010/11mar_figureaxis.htm

 

[ViewsofMars]

A more recent release from NASA on this topic:
http://science.nasa.gov/headlines/y2010/11mar_figureaxis.htm

Thanks D H,

From the url you presented dated March 11, 2010 plainly states, "On Feb. 27, 2010, the Chilean quake may have moved the figure axis as much in a matter of minutes as it normally moves in a whole year. It was a truly seismic shift—no pun intended.

So far, however, it's all calculation and speculation. "We haven't actually measured the shift," says Gross. "But I intend to give it a try."'


In the meantime I think I will stick with David Morrison, NAI Senior Scientist, has stated on March 11, 2010, which I presented earlier on page 3.

And thanks for being attentive and helpful. :)

 

[ViewsofMars]

But the point is moot the Earth didn't move the the ocean wasn't unsettled the sky didn't fall and apparently Viewsofmars took the mickey out of me.


CC

Hi Chris,

I don't know what a mickey is but whatever it might be, I'm glad it was removed by me. However, I never claimed 'the ocean wasn't unsettled'. And you are correct the Earth didn't move out of it's orbit around the Sun (if that is what you meant) but we did have an earthquake, and most definitely the sky didn't fall down upon us.

Keep those happy thoughts moving in the right direction.

 

[D H]

In the meantime I think I will stick with David Morrison, NAI Senior Scientist, has stated on March 11, 2010, which I presented earlier on page 3.

That quote by Morrison has nothing, absolutely nothing to do with the topic at hand. Nothing.

Look at the context of his response. He was talking to a lay person who asked "Could the fact that the poles are melting and there is unusually cold weather in other places be a sign of pole shifting?" Think about the huge magnitude of pole wander that would be needed to be the cause of recently observed losses in sea ice coverage. Hazarding a guess, I suspect a shift on the order of a degree (probably more) would be needed. This is the context of what Morrison meant by "if the pole shifted even a small fraction of a degree".

Moreover, the person was essentially asking if that shift might not have been detected. Not a chance! Very precise Earth orientation data are needed by many applications. Astronomy and GPS are a couple of examples. Knowing the Earth's orientation is such an important concept that the International Astronomical Union and the International Union of Geodesy and Geophysics jointly founded the International Earth Rotation and Reference Systems Service in 1987. Scientists know the Earth's orientation to an incredibly degree of accuracy.

It takes the US Naval Observatory a couple weeks to backtrack through all the data. After the fact, the error in the observed orientation of the Earth's rotation axis reduces to 0.03 milliarcseconds or less. In terms of "fractions of a degree", that is less than one 100 millionth of a degree. That is not the "tiny fraction of a degree" that Morrison was talking about.

Have you looked at the polar motion plots I have provided? (The link in post #50 and the polyhody plot in post #52.)

 

[ViewsofMars]

D H, be patient with me. I'm still working my way through the postings. I'm very intrigued.

[msg. 24]Where have those scientists been for the last fifty years? The short-term changes in the Earth's rotation rate and axis result from internal changes, not external. Google the term polar motion.

I hope you don't mind me back tracking a touch. It appears to me an example of the term "polar motion" would be the following, “Chao and Gross routinely calculate earthquakes' effects on Earth's shape and rotation. They also study changes in polar motion--that is, the shifting of the North Pole.” (How the Earthquake affected Earth, The Dec. 26th Indonesian megathrust earthquake quickened Earth's rotation and changed our planet's shape.) http://science.nasa.gov/headlines/y2005/10jan_earthquake.htm

So if you review my message 35 it seems to infer that David Morrison’s comment ‘if the pole shifted even a small fraction of a degree’ could be applicable to the above statement in quotes. Don't you think?

[msg. 24]You are looking at things wrong. It doesn't help that the lay articles imply that the Earth 'jumped' by 8 cm. That isn't what happened. It wasn't the Earth that moved; it was the Earth's axis.

So the Earth's axis as you apply in your first quote above has given me the impression I need to refer to polar motion. Don't you think?

Bare with me, I'm having a busy day, and hopefully will look further into your most recent comments.

 

[D H]

So if you review my message 35 it seems to infer that David Morrison’s comment ‘if the pole shifted even a small fraction of a degree’ could be applicable to the above statement in quotes. Don't you think?

Absolutely not. Once again, Morrison was talking in terms of the *huge* changes needed to change Earth's climate. A "fraction of a degree" would not cut it. On the other hand, a "fraction of a degree" (and remember, Morrison was talking to lay person) is something we can easily observe. In fact, we need to observe those changes. Modern instruments such as telescopes and GPS require incredibly precise knowledge of the Earth's orientation.

It might be worthwhile to review how incredibly small a milliarcsecond really is. A full circle is 360 degrees. A minute of arc, an arcminute, is 1/60 of a degree. An arcsecond is 1/60 of an arcminute. A milliarcsecond is 1/1000 of an arcsecond. What does that mean?

A dime held at arm's length is about 1 degrees wide. The bumpy part at the edge of a dime: that's about an arc minute. Now imagine dividing that bumpy edge another 60 times. That's an arc second. Now divide that another 1000 times, and you have a milliarcsecond.

Another way to look at how small the angles being discussed truly are: Stack one meter stick lengthwise atop another. Now put a vertical spacer so that at one end the meter sticks are still together but at the other they are separated by some measured amount. To get a one degree angle you will need to insert a 1.75 cm spacer between the two sticks. One arcminute: 0.29 millimeters. Use a standard sheet of paper as your spacer and you will have an angle of about 25 arcseconds. Use the very thinnest of tissue papers and the angle will still be over a second of arc. Now divide that tissue 1000 times, and you have a milliarcsecond.

 

[russ_watters]

Hi Russ,

First off, I'm a hetrosexual woman. I'm getting very upset by men calling me a "he." This isn't the first time here on physics forums it has happened to me where I HAVE HAD TO CORRECT the person for mistaking my identity. My question is why is it continuing? The impression I'm beginning to think is that women don't usually partake in discussions about Astronomy, Cosmology, etc. I've posted here before with valuable information. Also, I'm here to say, "WOMEN are welcomed to participate!"

I apologize. Yes, it is a combination of the fraction of women we get here, difficulty in writing in gender neutral language in English and my laziness that often has me assuming I'm addressing males.

 

[ViewsofMars]

D H, you did gave me the impression by stating “The short-term changes in the Earth's rotation rate and axis result from internal changes, not external. Google the term polar motion” that your statement did lead me to the conclusion that ‘the shifting of the North Pole’ was inclusive in your statement since you said ‘Google the term polar motion. Just being honest. Obviously, I mistook it wrongly. Ah well, we grow together.

The March 11, 2010 article from NASA that you presented also states at the bottom of the page, “In a few months Gross hopes to have the answer. Stay tuned.” Obviously, at this point in time Gross doesn’t have the answer. As he has said, "We haven't actually measured the shift.” I guess all we can do is be patient and wait since there isn’t any evidence or observation that has determined it to be a fact as of yet.

D H, it’s been a pleasure having this conversation with you. Thank you. I’ll be looking forward to seeing what Gross has to say in several months. I hope you will keep us informed about it.

I'm very interested in earthquakes. Lived through quite a few of them. We never know when they will hit. Not yet anyway. Hopefully, one day we will.

Have a wonderful day.

Mars

I apologize. Yes, it is a combination of the fraction of women we get here, difficulty in writing in gender neutral language in English and my laziness that often has me assuming I'm addressing males.

Hi Russ,

You are very thoughtful. I appreciate you taking the time to talk to me. Let's hope there will be more women in the future participating. I absolutely love SCIENCE! It's a valuable learning experience that enrichs my life in more ways than I can count.

Have a great day. You've made mine much brighter. :)

Mars

 

[D H]

D H, you did gave me the impression by stating “The short-term changes in the Earth's rotation rate and axis result from internal changes, not external. Google the term polar motion” that your statement did lead me to the conclusion that ‘the shifting of the North Pole’ was inclusive in your statement since you said ‘Google the term polar motion. Just being honest. Obviously, I mistook it wrongly. Ah well, we grow together.

You misunderstood.

There are essentially three ways the Earth's (or any rotating body's) orientation changes.
1. External torques. "External" means applied by some other body, "torque" is, in law terms , a twisting force. In the case of the not-quite-spherical Earth, the Moon and Sun apply torque to the Earth by grabbing the equatorially bulge gravitationally. The biggest change (and it is very big) in the Earth's orientation is also very slow. The Earth's rotational axis sweeps out a cone with a half angle of 23.4°, but it takes almost 26,000 years to complete a full cycle. This is the lunisolar precession. The Moon and Sun have other shorter term, but much, much smaller affects on the Earth's orientation. The 18.6 year nutation is the next largest term, 20 seconds of arc.

2. Inertial torque. This is a fictitious torque, akin to the centrifugal and coriolis force. Fictitious forces and torques arise whenever one does physics in a rotating frame of reference. Our Earth is a rotating frame of reference. This inertial torque is what is responsible for the Chandler wobble. It is not an external torque. It is instead a consequence of the Earth's angular momentum and angular velocity vectors not be collinear.

3. Changes in the inertia tensor. All kinds of things change the Earth's inertia tensor. Tides, seasons, continental drift, motion deep in the Earth's core ... and earthquakes. Any change in the Earth's inertia tensor has to be matched by a corresponding change in the Earth's angular velocity vector because angular momentum is a conserved quantity. (Angular velocity is not.)


The long-term variations in Earth's orientation most certainly arise from external causes. However, these long term variations are loooong term. 26,000 years long. The short-term variations are mostly internal (i.e., items numbers 2 and 3 above).

The March 11, 2010 article from NASA that you presented also states at the bottom of the page, “In a few months Gross hopes to have the answer. Stay tuned.” Obviously, at this point in time Gross doesn’t have the answer. As he has said, "We haven't actually measured the shift.” I guess all we can do is be patient and wait since there isn’t any evidence or observation that has determined it to be a fact as of yet.

It will take quite a while to see if there truly was an observable change. That 8 cm change is, over the short haul, just too small to see amidst the polar motion. As I noted earlier, the observed polar motion between Feb 25 and Mar 2 was 37.8 cm.

However, he is claiming an 8 cm change in the mean pole. Most of the polar motion averages out to nothing over the course of a year or so. The signal just might be visible in the mean motion. Gross faces several challenges in proving this: Noise (those seasonal changes are *noisy*), detection (that 8 cm change is *small*) and of course attribution. He will have to convince the scientific community that he has addressed all of these issues. So for now, it is wait and see.

 

[curiouschris]

For me this is my last word of the subject.

Nobody, including the press article you cited, said that the Earth shifted by 8 cm. The Earth's rotation axis moved, not the Earth as a whole. This continued misperception on your part

I never said the Earth shifted.

I said people are crazy if they think the Earth shifted. but that was the impression the articles (many of them) gave. Many of the contributors here concluded incorrectly that I thought the Earth shifted. No I didn't. read my first post.

I am again repeating myself here...

When someone says the Earth's axis has shifted most people, except the people of this forum will think that you mean the shaft about which the Earth rotates changed its alignment. The only reason I raised the point was because, hey! if the Earth supposedly did shift (and therefore I was wrong, in my belief that it DID NOT change its alignment). There would have been other ramifications (other than a few press articles misquoting a scientist) There may have been an alignment problem with telescopes, hence the choice of forum, and I am convinced other more dramatic problems like say the entire north pole shifting by 8cm and the consequences of that.

Now again because its been a few of lines since I wrote it last, I Do Not Believe nor ever have that the Earth shifted.

I think that's plain enough.

My apologies to ViewOfMars. I don't think I assigned gender but if my words bely that please forgive me. BTW to take the mickey out of someone is to call them a fool, in a roundabout sort of way. I never believed you did, but DH certainly inferred that.

 

[D H]

When someone says the Earth's axis has shifted most people, except the people of this forum will think that you mean the shaft about which the Earth rotates changed its alignment.

That is exactly what supposedly happened.

The only reason I raised the point was because, hey! if the Earth supposedly did shift

That is exactly what didn't happen. What supposedly did happen was that the Earth's rotation axis moved with respect to the Earth.

There would have been other ramifications (other than a few press articles misquoting a scientist) There may have been an alignment problem with telescopes, hence the choice of forum, ...

The operators of those telescopes, along with several other modern gizmos, need extremely precise knowledge of Earth's orientation -- and that is exactly why the International Earth Rotation and Reference Systems Service (IERS) was formed.

As has been pointed out, those telescopes are not so sensitive that a tiny 2.7 milliarcsecond shift will affect them. However, this change is cumulative. If that change truly did occur, the effects of it will build up over time.

 

[pixel01]

But the Earth's rotation is also slowly slowing down due to tidal friction...anyone have an estimate on that rate, and how the change in rotation speed due to this earthquake is comparable?

I am not sure about the rate of slowing down, but the process will end when our day is as long as a month (and the month then will be longer than it is now). We have only one semisphere who can see moon all the time just as stationary satellites.

 

[russ_watters]

A localised tsunami. but that's not a 5' tsunami that circled the globe. which is what you stated. If it did I didn't hear about that.

I said 3', but Hawaii is 6500 miles from Chile, which is a little more than 1/4 the circumference of the earth. Because of landmasses, it is tough for a tsunami to literally go all the way around the earth, but halfway would have the wave as spread out as it is going to get.

A wave is caused when I kick the the water at the beach. so what.

I don't see your point. Kicking the water doesn't cause a tsunami.

But take the entire globe and shift it by just 8 cm and I can't see that it wouldn't cause a massive disruption. You can't just pick up an ocean and move it.

The strength of a wave is a matter of amplitude and size. The way I understand tsunamis is that the amplitude is literally the amount the crust shifted. A 3' drop creates a 3' tsunami and a 3" drop would create a 3" tsunami...and direction matters: the ground moving laterally instead of up and down wouldn't cause a tsunami. I think that's why tsunamis are tough to predict.

 

[Philosophaie]

With reguards to the Sun, the Earth wobbles because of the Barycenter attraction of the Earth and the Moon and the not parallel axis of the Moon to the Ecliptic.