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

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Discussion Overview

The discussion centers around the movement of the Earth's axis, particularly in relation to the Chile earthquake and the concept of the "figure axis." Participants explore the implications of these movements for astronomical measurements and the nature of Earth's rotation.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • Some participants express skepticism about media reports claiming significant movement of the Earth's axis, suggesting that such changes would require recalibration of astronomical equipment.
  • Others clarify that the Earth's axis does fluctuate due to effects like nutation and precession, which astronomers account for over time.
  • A participant notes that the Chile earthquake reportedly shortened the Earth's day by a small fraction and shifted the figure axis by a few inches, raising questions about the terminology used in media reports.
  • There is a discussion about the mechanics of thrust earthquakes and how they affect the Earth's mass distribution, with some arguing that the net effect should be negligible.
  • Some participants mention the long-term slowing of Earth's rotation due to tidal friction and how this interacts with changes caused by earthquakes.
  • Concerns are raised about the accuracy of measurements related to Earth's rotation and the potential for significant changes due to large earthquakes.
  • One participant highlights the complexity of measuring changes in rotation speed, referencing neutron stars as an example of precise measurements in astrophysics.
  • There is a debate about whether the effects of tectonic plate movements during earthquakes can be expected to cancel each other out.

Areas of Agreement / Disagreement

Participants generally disagree on the significance of the Earth's axis movement and the implications for astronomical measurements. While some acknowledge the fluctuations, others question the extent and impact of these changes, leading to an unresolved discussion.

Contextual Notes

Participants mention various factors affecting Earth's rotation, including tidal friction, seasonal mass distribution changes, and geological events, indicating a complex interplay of influences that are not fully resolved in the discussion.

  • #61
For me this is my last word of the subject.

D H said:
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.
 
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  • #62
curiouschris said:
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.
 
  • #63
Matterwave said:
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.
 
  • #64
curiouschris said:
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.
 
  • #65
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.
 

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