Does Moon have North and South Poles ?

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Discussion Overview

The discussion revolves around the concept of whether the Moon has defined North and South poles, exploring definitions based on geographical and rotational characteristics. It touches on the implications of axial tilt and the definitions provided by the International Astronomical Union (IAU).

Discussion Character

  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants assert that the Moon has geographical poles that remain fixed when viewed from Earth.
  • Others clarify that the Moon's lack of a significant magnetic field means it does not have magnetic poles like Earth.
  • One participant explains that the IAU defines the North pole of astronomical bodies based on the axis of rotation relative to Earth's north pole, while others suggest an alternative definition based on the direction of rotation.
  • A participant mentions that Uranus presents a unique case due to its extreme axial tilt, complicating the definition of its poles.
  • Another participant notes that the Moon's 6.5° axial tilt leads to a phenomenon known as libration, causing its poles to appear to shift slightly over time.
  • There is a correction regarding the IAU definition, specifying it relates to the invariable plane of the solar system.

Areas of Agreement / Disagreement

Participants express differing views on the definitions of the Moon's poles, with no consensus reached on the best approach to define them. The discussion remains unresolved regarding the implications of axial tilt and the definitions provided by the IAU.

Contextual Notes

Some definitions and assumptions about the poles are dependent on the context of the solar system and the specific characteristics of celestial bodies, which may not be universally applicable.

call_naveen
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Yes geographically.
The bit at the top is always at the top when viewed from Earth and the bit at the bottom is alwyas at the bottom.
It doesn't have a magnetic field (ok a very tiny one) so doesn't have magnetic poles like the Earth.
 
call_naveen said:
Thanks
Naveen

Yes. Poles of other bodies are defined by their axis of rotation.

The International Astronomical Union (IAU) definition of the North pole for astronomical bodies is the end of the axis of rotation that points in the same direction as the Earth's north pole relative to the plane of the Earth's orbit.

However, others argue that the North pole would be better defined as the one where the rotation appears anticlockwise when looking down on the object, and that definition could also be used for objects in isolation without reference to the solar system, including objects outside the solar system.

The majority of planets and other bodies in the solar system rotate in the same direction, so there are not many bodies for which the two definitions differ.
 
Uranus for instance is tilted by 90deg so it's rotation axis points in the plane of the orbit.
So the 'top' of the planet is a point on the equator and is constantly changing - like the 'side' of the earth. Not sure what you would call the poles of Uranus.
 
mgb_phys said:
Yes geographically.
The bit at the top is always at the top when viewed from Earth and the bit at the bottom is alwyas at the bottom.

Well, not exactly. The Moon has a 6.5° axial tilt with respect to its orbit. So it nods back and forth as seen from Earth so that sometimes the North pole is tilted slightly towards us and sometimes the South pole. This is known as the libration of latitude.
 
Jonathan Scott said:
The International Astronomical Union (IAU) definition of the North pole for astronomical bodies is the end of the axis of rotation that points in the same direction as the Earth's north pole relative to the plane of the Earth's orbit.

Close. The definition is "The north pole is that pole of rotation that lies on the north side of the invariable plane of the solar system."

Seidelmann, P.K. et al (2005), "Report Of The IAU/IAG Working Group On Cartographic Coordinates And Rotational Elements: 2003," Celestial Mechanics and Dynamical Astronomy, 91, pp. 203-215.
Preprint is at http://astrogeology.usgs.gov/Projects/WGCCRE/WGCCRE2003preprint.pdf.
 

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