Talk:Q190009
Autodescription — nutation (Q190009)
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Ambiguous Item edit
There are two related but separate phenomena which are unfortunately both named "nutation" or similar in most languages.
- A component of the motion of a freely rotating rigid object e.g. a top. See Nutation (English), or de:Nutation (German)
- A component of the rotating motion of a planet under the influence of gravitational pull by moons, other planets or the central star. See Astronomical nutation (English), or de:Nutation_(Astronomie) (German)
Both kinds of nutation involve small periodic deviations of the mean axis of rotation. Both are accompanied by a second kind of motion called "precession" (or "Präzession"). So everything seems to be fine and dandy. However, the nutation of planets cannot possibly the same type of motion as the nutation of a top. The nutation of a planet is caused by a constantly varying torque by the gravitational pull of other objects. By contrast, the nutation of a top is defined to be a component of motion without any torque at all. Obviously, the formulas used to calculate the amplitude and frequency of the nutation are vastly different. In particular, it is impossible to regard one phenomenon as a limiting case for the other.
The German and the English Wikipedia dedicate separate articles to the two phenomena (see the links above). In other language versions I see:
- Rigid-body definition and rigid-body explanation combined with the motions of the earth as an example (Spanish, Italian, Polish, Dutch, Russian). → inconsistent
- Rigid-body definition, rigid-body explanation and rigid-body example (Croatian, Norwegian)
- Astronomy definition and rigid-body definition in separate sections of a single article (Turkish) → not according to universal wikipedia principles (one article per concept)
- Definition and explanation matching ridgid-body precession, rather than nutation (Nynorsk) → just wrong
- Definition based on geometry of movements. No assertion on causes. Tops, planets and ammunition as an example (schottisch, finnisch) → does not match the definition given in physics textbooks
Not very surprisingly, the statements attached to this wikidata item are conflicting ("motions of the Earth", but also "\mathbf{\tau} = \mathbf{\Omega} \times \mathbf{L}"). The formula given is not useful to calculate the nutation of the earth. It is the formula connected to the rigid-body motion.
So what can be done to sort this mess? At minimum, there should be two separate items in wikidata for the two meanings. This would provide adequate goals for the German and the English article. But how about the other ~50 language versions, most of which misrepresent the item in some way? Are there any precedences?---<)kmk(>- (talk) 21:25, 28 April 2017 (UTC)
- I copied the above to the page on interwiki conflicts. See Wikidata:Interwiki_conflicts/Unresolved/2017#nutation_.28Q190009.29. -<)kmk(>- (talk) 02:58, 28 May 2017 (UTC)
- Actions to resolve the mess:
- changed the English label to make the meaning more explicit ( "nutation" → "nutation (astronomy)" )
- changed the German label to make the intended meaning more explicit ( "Nutation" → "Nutation (Astronomie)" )
- removed statements which referred to the rigid body meaning
- removed misleading JSTOR identifier ( http://www.jstor.org/topic/nutation/ ). The continuous is correct as it was copied from the introduction of en:wp . But almost all literature listed by this identifier refer to the botanical meaning of the word "nutation".
- -<)kmk(>- (talk) 23:37, 12 November 2017 (UTC)
- Actions to resolve the mess: