Universal/Cosmic Spin

I have the vague thought that Uranus spins opposite from the relative direction Earth spins. Any thoughtful analysis or follow-up would be appreciated.

this site says you are correct.
Praytell, what ever put the original thought in your head? Bad liquor? Mexican food? e-mails?

The original thought was in connection with the email today from “The Straight Dope.” It’s question was ‘do black holes rotate east to west?’

Thank you for your reply. According to the site you recommended Venus also rotates opposite Earth’s relative rotation.

I read recently that in the next ten years there are going to be larger and more precise telescopes. They have already found over 35 planets in the Milky Way. They are all larger than Uranus because of technology limitations on the current (amazing) telescopes.

Obviously, this is facinating. Another mind-blowing idea I just read was that the Universe is believed to be relatively FLAT. This one will take a while to understand… To be honest I will never understand: I am a simple, easily facinated, intuitive science artist.

Actually, Uranus would be best described as laying on its side. Its axis of rotation is tilted 98[sup]o[/sup] from the plane of the ecliptic. Since it’s over 90[sup]o[/sup], that makes it technically retrograde, but only by a little.

But which of Cecil’s columns does this relate to? Anyone have a link?

Welcome to the SDMB, and thank you for posting your comment.

The original post is referring to a Staff Report. The Staff Report link has not yet been posted to the main page. The fortunate souls who sign up for the Straight Dope mailing list receive advance notice of new Staff Reports. The Staff Report will appear on the front page in due time.

Since the article is a Staff Report, not a Straight Dope column, this thread is leaving the «Comments on Cecil’s Columns» forum and going to visit my colleague C K Dexter Haven in the «Comments on Staff Reports» forum.

moderator, «Comments on Cecil’s Columns»

Yeah, Uranus and Venus are the reason why I said “most of the arrows” and “approximately the same direction”. I’m aware of the unusual rotations, I just didn’t think it was worth going into that much detail.

I’m having a little problem wrapping my brain around the idea of planets rotating in opposite directions. Sure, the earth rotates from left to right when I’m looking north, but right to left when looking south. East and west it seems to me are arbitrarily assigned and only have relevance with respect to the earth. Rotations are generally described as clockwise or anticlockwise, but it still depends on which pole is your reference. I suppose it is possible that if the axes of rotation are parallel for the planets in question that one frame of reference could be the basis for qualifying the rotations, but that seems highly unlikely.

Might help if you think in the terms of equators rather than poles, grienspace.

Standing on the Earth’s equator, able to see clearly all the planets with naked eyes (an imaginery scenario, of course) – a planet with features moving opposite to your own spin (to the right) would have, relative to you, reverse rotation. I agree that it’s difficult to visualise.

Saw in a documentary called Earth Story that, but for the fact that we have the Moon, we may have been the Uranus of the inner planets …

And the Staff Report being discussed is:
Do black holes rotate east to west?

By definition, the north pole is the one that’s rotating counter-clockwise when you’re above it, looking down.

In practice, the solar system is roughly two-dimensional. Except for the Oort cloud (which is more or less a sphere), all the planets and most of the lesser objects orbit in the same direction in roughly the same plane, and most of them also have their equators in more or less the same plane, and their north poles pointed in more or less the same direction as the Sun’s north pole.

But some have their north poles pointed in the opposite direction, and Uranus is practically turned sideways. No one really knows why.

grienspace, don’t think of it in terms of just Earth. Think of it in terms of the Solar System.

In the SS, the planets are strewn out such that they basically fall in one plane. (Pluto is the exception.) This plane of orbits is called the ecliptic. In this plane, all the planets circle the sun in the same direction.

Now use that as the reference. The Earth has the north pole up based on this reference, and rotates clockwise when viewed from above the NP. If you use the direction of orbiting the sun to establish up, and get over the planets, then you see which way they are rotating. Venus is backwards, or retrograde, from this orientation. Uranus is on its side.

This website is the Nine Planets pages.

It has pictures of the layout of the orbits. You can see the plane of orbit of the ecliptic, and Pluto is skewed.

You can also follow the link to each planet, and learn more.


JWK said

But don’t poles shift over eons? That’s why North poles point in diff. directions. Or am I confusing Magnetic north and other stuff?

living in a one-dimensional world, here!

grptdpdrrpt! CCW.

samclem, not sure if you’re confusing things or not. The Earth’s north pole is wobbling over 27,000 yr periods. It’s called precession. The amount of wobble is not extensive. Nothing like wobbling down to the plane of the ecliptic and then back up. The magnetic pole is moving. It has something to do with the core of the Earth, so it isn’t rigid. And then there appear to be periodic reversals of the magnetic field. No one knows why.

It is possible (likely?) that other planets have a precession, but not all have a magnetic field.

The magnetic poles completely shift direction every so often, and are constantly wandering around a bit. The rotational poles, on the other hand, regularly precess in the plane of the planet’s orbit, such that the axis slowly (over a period of thousands of years) sweeps out a cone perpendicular to the orbital plane. In other words, Earth’s axis is always pointing 23.5[sup]o[/sup] away from “Solar system North”, but in different directions. However, barring catastrophic events like a collision with another planet-sized body, they never completely reverse.

I just saw Irishman’s post, and yes, all planets precess, but to varying amounts, depending on the distance from the Sun and the amount by which the axis is tilted. There’s a lot more variability in the magnetic fields, among planets, because it depends on the source of the field: Gas giant fields will change much more rapidly than those of rocky planets, and the Sun’s field reverses every 11 years.

Irishman said

I was, you’re right. Mustavbeen the bad liquor.

In the Staff Report, Chronos said:

Just a slight clarification–that would be like a ship’sscrew (aka propeller). Otherwise we have to contemplate the Great Cosmic Screwdriver, and I’ll bet we’d all prefer not to.

(And, no, “Mysterjinx” is not me–I know what designations like “east” and “west” pertain to.)

“Flat” means Euclidean (non-diverging/non-converging topology of spacetime), not “flat like a pancake”.

The axis of rotation wobbles. The magnetic poles can shift (even reverse) over geologic timeframes.

Well, wouldn’t flat/non-converging mean that it is “flat like a pancake” in four dimensions?
Just like a 2-D pancake would be flat in 3-D.

OK, put it this way: “Flat” means that you don’t have to learn any funky new Riemannian geometry to talk about it; the stuff you learned in high school will do just fine. Head feel any better yet, ihrkelings?

Well, physicists general consider curvature of space as an interior property, not an exterior one, so you don’t need to invoke a fourth dimension to discuss 3-d space, even if it is curved.