Eliminate the Seasons?

I'm going to regret posting this. Recently, Rufus Hound tweeted (for reasons unclear to me)

Anyone? How do we eliminate the seasons. Someone must know. (source)

and

If we all start running West, we can stop the world spinning, then every day will be this long. No, hang on, that means it'll never be night (source)

To which I tried to respond in tweet form (starting here), and it took far too many tweets (sorry Rufus). Rufus retweeted a few (sorry Rufus' followers) - and I thought I'd better tidy things up.

First of all, let's understand why we have seasons. The earth goes around the sun. It does this once a year. The earth spins on its axis. This gives us days. The axis is tilted. The northern hemisphere is tilted toward the sun in June, and the southern hemisphere is tilted away. This means that the daytime is longer in the north and shorter in the south. In december, the axis is pointing in the same direction, but the earth is on the other side of the sun, so the southern hemisphere gets more daylight.

The longest days and nights are called solstices. Thus we have Summer and Winter Solstices.

In between the two, we get equinoxes. These are when the axis neither tilts toward or away from the sun.

To a decent approximation (i.e. not quite true), the Earth's axis always points the same way in space, at the moment it's roughly aligned with polaris, aka the pole star. When I said 'not quite true' this is because the axis wobbles, much as a spinning top does. It's an effect called 'precession of the equinox' for various technical reasons. It takes over 26000 years to do one wobble, so you won't need to worry about it much, and it doesn't affect the thrust of this post.

If any of the above (except perhaps the precession bit) is a mystery to you, follow the links.

Okay, let's get back to @Rufushound (sorry to have forgotten you for a while there). He suggested we all ran west. Let's take that at face value and see what it implies.

The sun 'rises in the east and sets in the west', so if we look down on the north pole, the planet seems to spin anticlockwise. If we all ran west, the planet would spin that bit faster (a negligible amount, it's true). However, the total angular momentum of the system would be unchanged, so when we all stopped running, the spin would be restored (essentially when speeding up we pushed off the earth changing its spin one way, and when we slowed down, we changed its spin back again. The angle of the earth's tilt WOULD change a little whilst we were running, but it wouldn't be a permanent change (and I haven't thought through if it'd make the angle bigger or smaller, maybe later).

We would have had a long term effect though. The precession will have been altered a little. Not much, true - this doesn't affect the seasons at all, and so does not speak to Rufus' question.

As an aside, the moon's tidal effect is slowing down the spin of the earth, and the days are getting longer - again, this is a very small effect.

Suppose we could put a giant knitting needle through the earth's axis and push it 'straight', let's put aside the need for 'a firm place to stand' and imagine building two big towers, one at each pole with a rocket on top to push the earth upright. Weirdly, this would not have the desired effect, If you try to straighten a big spinny thing in this way, it tends to move to the side. It's one of those things that even when you understand it, it's 'still a bit magic' in the words of Richard Feynman. This link gives some idea as to the weirdness of spinny things.

Okay, let's suppose we COULD straighten the axis, so that it was perpendicular to the orbital plane. Daylight would be 12 hours, as would nights. No seasons, right?

Wrong.

There would still be a weak seasonal effect as the orbit of the planet is elliptical. We are actually a bit closer to the sun in december than in june (weird, but true). So, in december, it'd be that little bit warmer than in june. Also, as with now, the solar day would be a bit longer in december.

Why is that? The earth takes 23 hours and 56 mins to spin once, that's called a sidereal day, the extra four minutes is as we've moved around the sun a bit, this is a what you normally think of as a day, a solar day and it averages to (roughly) 24 hours. In december we're closer to the sun and so moving faster, so extra spin needed to keep the sun at its highest at local noon .

This means that even if the Earth's axis were not tilted, we would still get some, admittedly small, seasonal variation due to our changing distance from the sun.

If we could correct that, we would eliminate the seasons. We wouldn't eliminate weather, though - (but weather would be very different). Nor would we eliminate long term changes as there'd still be variation in solar activity, atmospheric makeup, etc.

.... and then, I haven't even touched on all the issues about energy requirements, the amount of stuff you've have to throw off the planet at high speeds from your rockets to have an effect and so on.

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Oh, one more thing, and to end on an unbecoming snarky note. To those folks who saw this conversation on twitter and made disparaging comments - try reading a book. Knowing stuff is never a bad thing.

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To those who thought Rufus' question was silly. Why, yes it was. Silly questions can sometimes be interesting, and it was interesting. I hope what I've hacked together will show you why.

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Caveat: I wrote this at the end of a long day, based on tweets made whilst watching Wimbledon and trying to get some paperwork done at the same time, both unsuccessfully. I want to get back to the tennis, so this may contain slips and typos. With more time, I'd have put in pictures and stuff. I hope the wikipedia links will do (remember, wikipedia is a secondary source, not primary research - it can be edited by idiots). If you spot an error in the above, please do feel free to point it out in a civil way using the comment form. Similarly, if you have questions use the form (though I won't promise a fast reply, but someone else may be able to help you in the meantime). I'll avoid carrying on this conversation on twitter!