[If you have no idea why a series of posts about ATVs is now discussing pre-historic climate, all I can say is I warned you it would get weird. Plus, it all works out in the end.]
My dog died and I lost all sense of time and space, proportion or reason. I put all thoughts of buying anything out of my head. I couldn’t afford even a tiny bit of worldly concerns. Time would pass and I would recover, but for a while I just held on and let the planet rotate.
So… lets talk about planetary rotation. I’m going to oversimplify here because I’m a dumbass blogger trying to tell a story and not an astrophysicist. As I understand it, I’m more or less telling the truth. If I missed something significant, tell me in the comments.
So here goes; the Earth hangs in the void, spinning. All things that spin, rotate about their axis.
It would make sense that the earth’s rotation be exactly perpendicular to the plane of its orbit. That’s how I’d do it. But I’m not God.
The axial tilt (Earth’s obliquity) is somewhere around 23 degrees. Pretty shoddy workmanship if you ask me. If I welded a Subaru axle that badly, the damn thing would blow up.
Then again the tilt, as we all know (or should know) is the root of our seasons. Maybe God knew I liked fall colors. He certainly made clever arrangements to provide North American deciduous trees with a reason to go out in a yearly blaze of glory.
I knew all that. Unless you went to college for something that’ll never merit your student loan bills, you probably did too. Think about it; a couple degrees of tilt is why I hit -40 in winter and 100 degrees in summer… and never the opposite. It’s a big deal.
What I didn’t know was that the tilt has a periodicity. The tilt, apparently, moves.
OK fine, so what? Well if a few degrees of tilt, staying exactly constant in the scale of years and decades is the reason my lakes are frozen now and I’ll be swatting mosquitoes in a few weeks… what about variation in the tilt over centuries.
Enter Milankovitch Cycles. If you’ve been steeped in a modern college and think driving an SUV in August kills penguins in January… you may want to sit down for this next part ’cause this is going to hurt your delicate noggin.
About a hundred years ago. Long before Al Gore roamed the Earth, Milutin Milankovic worked out that eccentricities in the earth’s orbit may have something to do with cycles of ice ages. Remember my last snowflake warning? Well here’s another one. If you’re steeped in modern eco-think you might have to let this one settle a bit; we’re still in the ice ages.
This guy is smarter than you.
This is cute and all, but Milankovitch Cycles cause a side effect that most folks don’t know. Roughly 6,000 years ago about half of what we call the Sahara desert was savanna:
The drier portion of what we now call the Sahara desert was steppe:
Due to orbital eccentricities it turned to dunes This is the Sahara right now:
Compare those photos. That’s some serious change. (Note: I mentioned this whole Milankovitch thing last fall.)
With my dog dead and my heart set on sandy beaches, I thought of the Sahara. A desert that bloomed out of nowhere and kicked the shit out of whatever humans inhabited the region. The earth changed in human time.
I had a desire to see the Sahara… to touch the Earth in a place that’s gone from Steppe to Death.
Of course, I live in Northern North America, none of that shit went down in my area. We were too busy having every living thing utterly obliterated by massive unending sheets of ice.
Well what have we here? The universe never fails to amaze. These are photos of the Athabasca Sand Dunes of Canada. This isn’t directly caused by our Serbian braniac friend Mr. Milankovitch and his space math; it’s due to the secondary effect of ice sheets retreating (which definitely had something to do with space math!). The retreating glaciers trapped behind them a small cold piece of something that you’d associate with camels.
This is Canadian.
This is Canadian too.
No shit. There are deserts IN CANADA.
Canadians. Some with theories about an ostrich… allegedly.
Still thinking of maple syrup and hockey? This is Canada.
Irresponsible Canadians; with guns.
Walking on giant dune, William Dune Field, Athabasca Sand Dunes, Saskatchewan
Who can fail to be amazed by our friends to the north? Those clever buggers squeezed a piece of Morocco into a spare section of the frozen North. I mean, who would look for sand dunes that far north?
In mourning for my dog, I sought solace in the simple joy of learning new things; in this case geography. I’d given up all hope of buying anything like/near to/related to/of a kind to an ATV. Also, it felt like somehow this had to do with Canada.
I’d started with a Canadian (Michael and his charming dog Esme) driving an Argo (made in Ontario), through Urals (made in Russia), test drove several Polaris (made in Minnesota), almost lit on a Rokon (made in New Hampshire) until I fell on the ice, and then had nightmares over my final decision to finance a Can Am (made in Ontario).
I let the whole thing go. The universe would tell me what to do.
And the universe did know what to do. It solved the whole thing. It sent another Canadian. I wound up watching videos on FortNine.
FortNine has hundreds of videos but one, as if inspired by the universe, set me on a new path. It was as if it were meant for me. If you’ve seen the video, you know what I did. If not, I will post the link. Stay tuned.
A.C.
P.S. Check out photojourneys.ca for their amazing photography!
I’m praying you are calling it Ishmael
More sand dunes in Canada – look up the Carcross Desert.
There are also active dune fields along Lake Michigan. Active and moving and growing and dying.
One field even is so tall that there are trees underneath it, and the trees have rotted and left huge vertical tubes that can open up and suck people, animals and vehicles down them.
https://lakemichigansanddunes.com/
Wicked weird, huh?
And if you are ever on the east coast of Florida, and a hurricane is approaching, just make sure you move far enough inland off the shore that you are on or past the first or second dune ridge. Which will put you 20′ or so above sea level.
Dunes… They are everywhere.
The equations you want are called the Euler equations. You can derive them by working out the inertial rate of change of the moment of inertia tensor in the body frame. https://en.wikipedia.org/wiki/Euler%27s_equations_(rigid_body_dynamics)
Because of the nonlinearity of the dJ/dt*w term, you can get some pretty weird motions of the axis of rotation. (Sans torque, the angular momentum is conserved and points in the same direction in space. The moment of inertia ellispoid rotates though, so the angular velocity rotates.)
The Russians noticed the “tennis racket theorem” on one of their space missions: The periodic flipping of an object rotating about the intermediate principle inertial axis, and promptly classified it. They thought it might predict the planetary axis periodically completely flipping over, and decided that it must be kept secret. (because we might not notice! eyeroll) (I’m pretty sure the Earth is oblate with symmetry about it’s minor axis, so we should be safe from this. But it might not be *that* crazy since small asymmetries could still make things unstable over very long timescales.)
Play the video here: https://en.wikipedia.org/wiki/Tennis_racket_theorem
PS: I have a matlab script that animates this. I haven’t made a movie of it though that you can see without matlab.
What might keep planets safe from that flipping effect is that nothing on the scale of a planet is completely rigid. Also there are gravity torques of the sun and moon on the Earth due to Earth’s obliquity.
Also, you’re never going to catch a planet rotating (for very long!) about any other than the largest moment axis due to the elasticity of the constituent matter.
Pingback: Friday Links | 357 Magnum