What is the Role of Earth's Axis in Copernican Astronomy?

  • Thread starter Franco Malgari
  • Start date
  • Tags
    Movement
In summary: Then it would fell apart because it's not a stable system. Real one is stable, and that's way more important than axis orientation. So, the third motor is just an unnecessary complication that doesn't really matter because it doesn't affect the outcome of the model (unless you're building a scientific-grade model, in which case M3 becomes important).In summary, Copernicus' third movement was a historical mistake that is not considered in modern astronomy because it is unnecessary and does not affect the outcome of the model. The Earth's axis remains fixed with respect to the stars due to its gyroscopic effect, and any slight changes in this orientation are accounted for in the IAU 2006 rotation-nutation-pre
  • #1
Franco Malgari
10
0
Astronomy considers only two main movements of Earth, rotation around its axis in a day and the revolution around the Sun in one year;
because astronomers do not consider the rotation of the Earth's axis around itself in a year?
 
Astronomy news on Phys.org
  • #2
Welcome to PF!

Hi Franco! Welcome to PF! :smile:
Franco Malgari said:
Astronomy considers only two main movements of Earth, rotation around its axis in a day and the revolution around the Sun in one year;
because astronomers do not consider the rotation of the Earth's axis around itself in a year?

I'm not really following you …

the Earth's axis rotates once every 25,772 years, not once a year … see http://en.wikipedia.org/wiki/Precession_of_the_equinoxeshttp://en.wikipedia.org/wiki/Precession_of_the_equinoxes [Broken]

(or do you mean the extra day … the Earth rotating 366 1/4 times in a year of 365 1/4 days?)
 
Last edited by a moderator:
  • #3
Te Earth's axis remains in the same position throughout the revolution around the Sun, turning always to the stars.
If I made a model of planet earth-sun I forced to use a motor to spin the globe in 365 days just to keep the Earth's axis always stationary relative to the revolution around the Sun ..
It's not precession..
 
  • #4
What is the effect of this "third motion"? It does not seem to show up in the many long term photographs which are taken by the Earth's telescope.

Perhaps we are still not understanding you.
 
  • #5
Please, read on Google "third movement of Copernicus":
 
  • #6
This is the question:
 

Attachments

  • moti.gif
    moti.gif
    8.5 KB · Views: 778
  • #7
If I understand the situation correctly there is no third movement, so there is no need to consider it. It was just an artifact of older models.

If you put a small globe on the turntable, axis will change its direction in the space, and it was already obvious in precopernican times that it is not happening - Earth axis always points in the same direction. To explain the difference between this type of the model and reality third movement was introduced. But Earth is not revolving around the Sun as if rigidly attached to some disc, it is more like a gyroscope.
 
  • #8
Franco Malgari said:
Please, read on Google "third movement of Copernicus":
Copernicus' third movement was a completely unnecessary and useless encumbrance. Copernicus envisioned that the natural motion of the Earth would be to have the Earth's axis always tilted toward the Sun. Since this natural motion wasn't what was observed, the axis must have been rotating so as to keep it aligned with the fixed stars.

A better model of the natural motion of the Earth's rotation is that the Earth's rotation axis would remain fixed with respect to inertial space unless torques act to change the Earth's angular momentum.

Franco Malgari said:
Astronomy considers only two main movements of Earth, rotation around its axis in a day and the revolution around the Sun in one year;
because astronomers do not consider the rotation of the Earth's axis around itself in a year?
That is good enough for most amateur astronomers, but not for professional ones. Neither the Earth's angular momentum nor its angular velocity are constant. Astronomers worry about precession, nutation, polar motion, changes in the Earth's rotation rate, etc. There are thousands of terms to the IAU 2006 rotation-nutation-precession model, and even that doesn't capture all of the motion. There are variations that can't be modeled (yet). If you need extreme precision in the Earth's orientation (e.g., microarcsecond pointing) you have but no choice to use the polar motion and ΔUT1 values which are updated daily by the IERS.
 
  • #9
Franco Malgari said:
Please, read on Google "third movement of Copernicus":

Franco, this is ridiculous …

all the references seem to be to forum threads such as this.

If you have an proper reference, please specify it in future instead of making us hunt for it. :frown:

There is no third movement of Copernicus (other than a historical mistake).
 
  • #10
tiny-tim said:
Franco, this is ridiculous …
Wikipedia article on Copernican heliocentricism, http://en.wikipedia.org/wiki/Copernican_heliocentrism
Earth has three motions: daily rotation, annual revolution, and annual tilting of its axis.​
J.H.Bridges, Tycho Brahe, in Contemporary Review, February 1902
http://books.google.com/books?id=30IeAQAAIAAJ&pg=PA197
The third was a movement by which, in revolving around the Sun, the Earth maintained its axis in a direction parallel with itself during the whole circuit. Without this third movement Copernicus imagined that the Earth's axis would always be inclined toward the Sun (or rather toward the axis of the ecliptic) at the same angle ...​
Hilary Gatti, Giordano Bruno and Renaissance Science,
http://books.google.com/books?id=9cYumhwTQP8C&pg=PA73
Having defined his third movement in terms that allow the axis of the ecliptic to remain constant, Copernicus then explains that this constancy is not absolute. The direction of the axis slips back very slowly over the centuries with respect to the sphere of fixed stars, giving ruse to the phenomenon known as the precession of the equinoxes. ... By explaining the precession as a very slight movement of the axis of the Earth in its orbit around the sun, Copernicus had much simplified the phenomenon of precession, and he was quick to point this out as a distinct advantage of his system over the traditional geocentric astronomy.​
So essentially Copernicus' third motion is precession, but stated in a form that is a bit non-scientific, at least by our standards.
 
Last edited:
  • #11
tiny-tim, I think the turntable analogy explains it pretty well. I can try to take a picture if you have problems figuring out what I mean.
 
  • #12
But if I had to build a model, I use three motors:
 

Attachments

  • 3 motor.jpg
    3 motor.jpg
    12.9 KB · Views: 437
  • #13
First - model is not the reality, model is just a model. Sun/Earth system doesn't contain a single motor, yet it works for over 4 billion years.

Second - you don't need three motors. You can use M1 and M3 only, just mount the globe on the bearing and gyroscopic effect will take care of the axis stabilization, just like it does in reality.

More importantly, if you could build a friction free model without motors, and put it into motion by spinning the Earth and pushing it around the Sun, it would replicate the real Solar system for ever.
 
  • #14
This is the other side of the coin from the more common problem people have with the two motions of the moon...
 

1. What is the significance of the third movement of Copernicus?

The third movement of Copernicus refers to the shift in scientific thought known as the Copernican Revolution. This movement challenged the geocentric model of the universe, which placed the Earth at the center, and proposed the heliocentric model, which placed the Sun at the center.

2. How did Copernicus come up with the idea for the third movement?

Copernicus was a Polish astronomer and mathematician who studied the works of ancient Greek astronomers and observed the movements of the planets. He used his knowledge of mathematics and observations to develop the heliocentric model of the universe.

3. What evidence supports the third movement of Copernicus?

One of the main pieces of evidence is the retrograde motion of planets, which can be explained by the heliocentric model but not the geocentric model. Additionally, the heliocentric model can accurately predict the positions of planets and other celestial objects.

4. How did the third movement of Copernicus impact scientific thought?

The third movement of Copernicus was a significant turning point in scientific thought and marked the beginning of modern astronomy. It challenged long-held beliefs and paved the way for future scientific discoveries and advancements. It also sparked debate and controversy among scientists and the Church.

5. What is the legacy of the third movement of Copernicus?

The third movement of Copernicus revolutionized our understanding of the universe and paved the way for future scientific progress. It also influenced other fields such as physics and mathematics. Copernicus' work laid the foundation for modern astronomy and continues to inspire scientists to this day.

Similar threads

  • Astronomy and Astrophysics
Replies
27
Views
2K
  • Astronomy and Astrophysics
Replies
24
Views
1K
Replies
5
Views
1K
  • Astronomy and Astrophysics
Replies
20
Views
1K
  • Astronomy and Astrophysics
Replies
1
Views
1K
  • Special and General Relativity
2
Replies
39
Views
2K
  • Astronomy and Astrophysics
Replies
2
Views
2K
  • Astronomy and Astrophysics
Replies
3
Views
1K
  • Astronomy and Astrophysics
Replies
7
Views
917
  • Astronomy and Astrophysics
Replies
7
Views
5K
Back
Top