Minor nitpick: Isn’t the ecliptic defined by the plane of the orbit of Earth? Uranus’s angle of rotation is defined relative to the plane of its own orbit (O.K., its Uranus’s ecliptic, but not that of Earth.) It’s trivial in Uranus’s case, since the plane of its orbit is less than 1[sup]o[/sup] off Earth’s, but it would be significant for Mercury or Pluto.
Given this, wouldn’t the tilt of the axis of rotation of Venus be decribed as close to 180[sup]o[/sup]? (Sorry, the websites I checked didn’t give axial tilts.)
The ecliptic can be defined in one of three ways: Earth’s orbital plane, Jupiter’s orbital plane, or the plane perpendicular to the total orbital angular momentum in the Solar System. In practice, it doesn’t really matter what definition you use, since all of the planets which aren’t Kuiper belt objects (no offense, Pluto) have orbital planes within a degree of each other, and Pluto hardly adds anything to the total, being so small.
Venus’ inclination is, indeed, sometimes given as a number in the vicinity of 180[sup]o[/sup] (don’t recall the actual number offhand), but it’s also sometimes given as a small number and just marked “retrograde” in parentheses.
Thanks Chronos, now I have more to think about. Why wouldn’t space be measured in as many dimensions as anything else? It moves, doesn’t it? Isn’t expansion a concept related to the fourth, and higher, dimensions? Just wondering. I will try to learn more about this topic. Also, I do agree that light pollution is excessive.
That’s the way any rational person would define it. But the IAU is not a rational person, but rather a committee. So naturally they defined it some other way.
As I pointed out in the other thread on this topic, the official definition of a north pole is the one that points to the north ecliptic hemisphere. And I believe the ecliptic in this case is that of the Earth’s orbit.
That’s why the inclination of Uranus is often listed as 82° (retrograde) rather than 98°. The retrograde number is the official number.
Actually I always had a lot of trouble figuring out how some planets got to have retrograde rotations, assuming planetary rotations are a remnant of initial eddies in the original solar nebula, as influenced by subsequent collisions. (Is this correct? How about the assumption that all the initial planetary eddies would necessarily have the same handedness?). Seems like it would be difficult to set up a collision or series of collisions that would actually reverse the direction of the rotation. However, it’s a lot easier to visualize if Venus and Uranus are just “flipped”, upside down in the case of Venus, and halfway over in the case of Uranus, so their original north pole is now facing solar-system south.
So Chronos (or anyone), what say you? Are Venus and Uranus rotating backwards, or are they just upside-down?
The more I think about visualizing this, the more I think about some of the fractals drawn from the Chaos Theory. The universe seems to be one huge paisley, our galaxy one cillia on it, and our solar system, one little blip on the cillia. Sounds like the opposite rotations could fit into this visual. Any insight into this would be welcomed. Evelyn.
Well, since matter curves space, you’d still need non-Euclidian geometry to describe portions of our flat universe.
And as for flat in 4-d, I wasn’t positing the existence of higher dimensions for the universe to be embedded in, was thinking of it more as a visualization exercise for the topic starter.