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Oi! Dakka!

Got a 'not sure why I want to know, I just do' science question for our resident boffins.

Don't worry, it's not Flat Earth twaddle or owt like that.

But it's to do with the Earth's rotation, and whether it's conceivable for the axis upon which it revolves to change.

Now, I know we wobble about a fair bit - but could it permanently shift. Extreme example would be the planet flipping in its orbit, so the two poles wind up in the equatorial region?

Do you mean, "before the end of the week?" or do you mean "before heat death of the universe?"

Also, are you referring to the magnetic poles or the rotational axis?

 Mad Doc Grotsnik wrote:
Oi!

 Mad Doc Grotsnik wrote:
boffins

 Mad Doc Grotsnik wrote:
twaddle

 Mad Doc Grotsnik wrote:
owt

Question, do you have a browser plugin that translates into 5x British, or do you manually type that?

I work with a good number of Brits. I can't say whether it's a plugin or it's natural, but I can confirm from their emails that they all have it too.

I believe the axis of rotation has moved, though not anything as dramatic as you suggest. This was a very long time ago (or so goes the theory). I don't really remember any details, so I guess I can't help much, other than to say I believe the answer is yes.

Pretty much 'ever'.

I really don't know why Mr Brain wanted to know this. But he does!

And Ouze....not our fault you can't speak proper English :p

It certainly can for whatever raisin

IIRC Neptune or Uranus is floating in space side ways though scientists believe it wasnt always like that. some kinda catastrophic something caused it to go side ways.

There are also effects that can tidaly lock a planet to so rotation totally can be altered.

id figure if the crust of the planet was hit hard enough it could shift the rotational axis. and IIRC the magnetic axis has changed in the past.

but what do i know im not a scientist

https://en.wikipedia.org/wiki/True_polar_wander

Takes a long time. 1 degree per million years, apparently.

I believe it's generally accepted that the magnetic poles will suddenly flip "occasionally", for geological periods worth of time between the "occasionally". I imagine that would make for an interesting day were it to occur without warning in this casual modern world.

The rotational axis has been slowly slipping as I recall from an article I read some time ago. I believe the cause was attributed to climate change, if you believe in such things, and literally anything but climate change if you don't.

The Earth's rotation suffers three forms of shifting called Milankovitch Cycles, caused by the momentum of the rotation around the Sun and gravity from other celestial bodies.

M. Cycles can be divided into three aspects:
- Eccentricity: The change in the orbit around the Sun from circular to elliptical, occurs on a 100,000 year basis
- Obliquity: The angle of the Earth's orbit, which at the current period is 23.5%, occurring on a 40,000 cycle basis.
- Precession: The facing of the Earth's poles at various points of the year (In it's simplest explanation) on a 20,000 year cycle.

Your question would relate to Obliquity, and maybe Precession. The Earth's orbit does indeed vary between 21-24 degrees, similar to how Uranus is rotating at 90 degrees. This small variation is believed to have a role in glacial and interglacial climate change but it's fair to conclude that we will never see any noticeable change in our lifetime due to this.

Source: Master's degree in Geography.

 Mad Doc Grotsnik wrote:

But it's to do with the Earth's rotation, and whether it's conceivable for the axis upon which it revolves to change.

Now, I know we wobble about a fair bit - but could it permanently shift. Extreme example would be the planet flipping in its orbit, so the two poles wind up in the equatorial region?

It is possible but would take an incredible force to do so. As previously mentioned, Uranus rotates around an axis approximately 90 degrees from vertical. We don't exactly know why but the most likely explanation is a huge impact (or several smaller ones) shortly after its formation which knocked it off its original axis.

An impact large enough to accomplish such a huge shift in the Earths motion would most likely destroy all advanced life on earth from a combination of the shockwave and resultant tectonic activity, huge amount of dust thrown into the atmosphere, tidal activity, sudden climate changes and total destruction of the seasons as we know them, not to mention the potential altering of Earths orbit around the sun as the planets rotational motion is now altered.

Earth's axis does wobble a bit, tracing out a big circle in the sky (sort of). In the time of the Egyptians, the North Star was not Polaris, it was Thuban. In about 12000 years it will be Vega. Eventually it will rotate around a circle and come back to Polaris again. I think I've heard that it's a 25000 year cycle or something?

As to whether a catastrophic event could change it drastically, I'd say a large enough asteroid impact could do it. Anything that massive hitting the Earth would probably kill every living thing on it, though, so no one would even care after it was all over with. I could be wrong about this; I'm certainly not an expert. It just seems to make sense.

I think the sort of impact that would alter the axis of rotation would be violent enough to melt the crust at the same time.

I've also heard it said that the moon provides a stabilising force, and without it, the change in the rotation axis ("precession") would be much greater - to the detriment of the evolution of life.

also:

https://what-if.xkcd.com/10/

I would guess that as an alternative to direct impact the gravitational disturbance from a close pass by a suitably large object (e.g. A rogue planet) would also be enough to move the axis, but I guess the biosphere impact would be just as bad.

Fundamentally anything with the energy to move planets around is going to make a hell of a mess, unless it happens gradually over a very, very long time!

 Valkyrie wrote:
The Earth's rotation suffers three forms of shifting called Milankovitch Cycles, caused by the momentum of the rotation around the Sun and gravity from other celestial bodies.

M. Cycles can be divided into three aspects:
- Eccentricity: The change in the orbit around the Sun from circular to elliptical, occurs on a 100,000 year basis
- Obliquity: The angle of the Earth's orbit, which at the current period is 23.5%, occurring on a 40,000 cycle basis.
- Precession: The facing of the Earth's poles at various points of the year (In it's simplest explanation) on a 20,000 year cycle.

Your question would relate to Obliquity, and maybe Precession. The Earth's orbit does indeed vary between 21-24 degrees, similar to how Uranus is rotating at 90 degrees. This small variation is believed to have a role in glacial and interglacial climate change but it's fair to conclude that we will never see any noticeable change in our lifetime due to this.

Source: Master's degree in Geography.

You are completely spot on. Milankovitch cycles do appear to correlate with the frequencies embedded in climate change. And yes, it's the latter two that Mad Doc would like to know about.

There's also a fourth phenomenon, where the long axis of the elliptical rotation rotates around the sun over time - can't remember the period it occurs over.

A couple of people have mentioned that the geomagnetic poles have reversed in the past fairly regularly (so all our compasses would start pointing in the other direction) as evidenced by "striping" in the magnetic field orientations preserved in sea-floor crustal rocks. That's true, but it's a separate phenomenon from the physical rotation of the planet. We may actually be in the early stages of a magnetic reversal...

A planet can indeed shift it's axis. But for something as dramatic as shifting the poles to the equatorial region, that would take nothing short of collision with another planetary body. And even then, the planet's actual axis of rotation wouldn't likely change(IE: we would still spin about an imaginary rod through the north and south poles). It's just those poles orientation relative to the sun would change.

Even if that change in orientation could be done magically and without a cataclysmic effect on the Earth, the final result would do horrible things to the biosphere. You know how the polar regions get months of unending daylight in summer and darkness in winter? The entire Earth would be like that. when the axis of rotation would point at/away from the sun, one hemisphere would have daylight while the other would be in darkness. Three months later when the axis of rotation is tangential to the orbit, you'd have 12 hours daylight/12 hours darkness.

Would the axis not stay relative to the Sun though, just affecting which parts of the Earth are now the poles?

It wouldn't necessarily. A planet's axis doesn't have to line up perpendicular with it's orbit of the star.

Changing a planet's axis of rotation would be far far harder than changing where it is relative to it's orbit around it's star. It would involve stopping the planet's rotation entirely, and then making it rotate again on whatever new axis you want.

 Mad Doc Grotsnik wrote:
Would the axis not stay relative to the Sun though, just affecting which parts of the Earth are now the poles?

The axis of rotation will always remain relatively the same, there are slight changes over thousands of years to the point where there is more than one North Pole: the Magnetic North and the True North, where the axis of rotation actually occurs.

So if the Earth was somehow magically tilted onto its side without killing everyone in the process so rotational spin was "up" instead of "sideways". At the current equator you could go from arctic conditions to tropical and back to artic again in a single day? That would not be fun world to live on

GoatboyBeta wrote:
So if the Earth was somehow magically tilted onto its side without killing everyone in the process so rotational spin was "up" instead of "sideways". At the current equator you could go from arctic conditions to tropical and back to artic again in a single day? That would not be fun world to live on

Actually no. That wouldn't change much of anything in the short term. What would change is that for 3 months or so out of the year, one of the poles would face the sun and the other would face away. We'd spend 3 months with the equator facing the sun. Then another 3 months with the other pole facing the sun. And finally 3 more months with the equator facing the sun.

That would mean the poles would, over the course of a year, go between being a frozen wasteland to being a burning hellscape. During the height of winter and summer, one hemisphere would be in perpetual twilight while the other was shrouded in permanent darkness.

Life would really only be possible in the equatorial regions which would likely have a temperate climate.

While the Arctic was facing the sun, the ocean would become extremely warm. Lots of water evaporation would cause massive storms to flow down towards the equator. At the same time, Antarctica would be frozen over.

Then 6 months later, Antarctica would bake under perpetual direct sunlight. The land would be scoured clean of any water. The ocean would become very warm down there too, but because there would be less overall water evaporation, the storms would be less severe. This would likely be the planetary dry season. The Arctic would freeze over during these months.