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Forum » SpaceEngine » Feedback and Suggestions » Axial Precession in SE ((or is Precession the correct term?))
Axial Precession in SE
smjjamesDate: Saturday, 06.10.2012, 23:22 | Message # 1
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While playing around with the time step when setting up for a neat screenshot, I had a thought about whether axial procession is in SE (I was hoping that the rings would change orientation as the planets axis moved). However, it apparently isn't, so I thought it would be something cool to add for SE.

Not sure how planets with extreme axial tilts like 209 for this particular planet or planets that don't have a moon to stabilize the axial tilt would be dealt with though.

Also, I thought it was called Axial Procession, but wiki calls it Precession.





 
SpaceEngineerDate: Sunday, 07.10.2012, 08:54 | Message # 2
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Yes, this is called precession. It is used in SE for Earth, for other planets I have no data, and it is not calculated for procedural planets, because I don't know how to do this.




 
smjjamesDate: Sunday, 07.10.2012, 15:51 | Message # 3
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I thought it might be as simple as entering a common formula for all planets to use, but okay.




 
FastFourierTransformDate: Friday, 05.08.2016, 17:15 | Message # 4
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I'm sorry for reviving this old thread but I don't want to collapse the forum with a new one dealing with the same issue.

Quote SpaceEngineer ()
this is called precession. It is used in SE for Earth, for other planets I have no data, and it is not calculated for procedural planets, because I don't know how to do this.


I've found an interesting article where they calculate the precession for other planets of the Solar System. The axial precession we are talking here is what generates the precession of the equinoxes (forced precession), and it's caused by the inclination of the Moon's orbital plane (that contributes to the 69% of this precession) to the equatorial plane of the Earth, and the inclination of the orbital plane of the Earth to the equatorial plane (the contribution of the Sun). This configuration for the Earth-Moon-Sun system generates a torque on the planet and thus a giroscopic effect. The other kind of precessión is the Chandler Wobble (Free Eulerian Precession) and it's due to the mass distribution of Earth. In the article they explain how to calculate both teorically (reality is always much more complex but it could be a good aproximation).

The article arrives to this figures for the forced precession:


  • Earth - Torque is exerted by: Moon (69%) +Sun (31%) - Axis inclination: 23º.5 - Period of precession: 25.700 years
  • Moon - Torque is exerted by: Earth - Axis inclination: 6º.7 - Period of precession: 78,5 years
  • Mars - Torque is exerted by: Sun - Axis inclination: 25º.2 - Period of precession: 178.000 years
  • Jupiter - Torque is exerted by: Sun - Axis inclination: 3º.1 - Period of precession: 0,5 Myr
  • Saturn - Torque is exerted by: Sun (Titan exerts the 90% of the torque of the moons but even this torque is insignificant compared to that of the Sun) - Axis inclination: 26º.7 - Period of precession: 1,8 Myr
  • Neptune - Torque is exerted by: Sun - Axis inclination: 29º.4 - Period of precession: 23 Myr
  • Callisto - Torque is exerted by: Jupiter - Axis inclination: ~0º (imperceptible) - Period of precession: 200 years
  • Titan - Torque is exerted by: Saturn - Axis inclination: ~0º (imperceptible) - Period of precession: 200 years
  • Triton - Torque is exerted by: Neptune - Axis inclination: ~0º (imperceptible) - Period of precession: 65 years
  • Iapetus - Torque is exerted by: Saturn - Axis inclination: 9º - Period of precession: 29.000 years


Could this calculation be applied to SE to measure the forced precession for procedural systems? Satellites orbits, inclination to the orbital plane and distance to the star are needed as inputs and then you have the precession period. Maybe in some case could be something noticiable.

By the way the free precession, that generates the Chandler Wobble on Earth differs from the calculated value in this article (measured period: 434 days - calculated period: 306 days) due to the dependance on the density of the Planet. This is one proof of the existence of the mantle (more elastic planet that the one that was presumed in the calculations). So if Chandle Wobble is also implemented in SE, it would have to take into account the inner structure of the planet/moon. The effect on Earth is totally insignificant (the projected oscilation to the surface of the planet has an amplitud of 6 meters around the poles) but maybe in some configurations could be important.

I know this is not a very important issue to solve in SE but I would like to see more of these details on procedurally generated planets smile
 
Forum » SpaceEngine » Feedback and Suggestions » Axial Precession in SE ((or is Precession the correct term?))
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