Hey Crazies.
I don’t know if you’ve ever noticed, but there’s something weird about the night sky.
There are bright dots everywhere!
Most of them are very far away and stay pretty static relative to each other,
which is why, for thousands of years, we were convinced they formed a solid shell
around us.
Thankfully, we've learned that space has a lot more depth than that.
But in this narrow band across the sky, you’ll find the closest dots.
These are super weird because they’re some of the brightest in the sky
and, if you watch long enough, you can see them move against the background.
Those bright wandering dots are the Planets, which comes from the Ancient Greek:
“Planetai Asteres” meaning “Wandering Star.”
Actually, in Ancient Greek, the noun comes before the adjective
so it would be: “Asteres Planetai” or “Star Wandering.”
Whatever! It doesn't matter!
The point is, all the planets, the Sun, and the Moon are in the same part of the sky.
It’s called the ecliptic because it’s where all the solar and lunar eclipses happen.
That band also happens to pass through 12 star constellations called the zodiac.
Side note!
Constellations are completely arbitrary groups of stars
made up by people thousands of years ago probably with the help of some psychotropic
drugs.
Dude, I think it looks like a lion.
Have you been eating the mushrooms again?
Astrology is a form of magic from 4000 years ago.
Astronomy is a completely respectable science and science is what we do here.
End of side note!
So, to understand why all these objects are along the ecliptic,
we need to think 3-dimensionally.
The orbit of the Earth around the Sun is called the “Plane of the Ecliptic.”
How much another orbit is tilted from this plane is called its inclination.
For the other 7 planets and the moon, those inclinations are less than 10 degrees.
That means they all orbit in roughly the same plane.
But why? What's the deal with that?
Hmm, that's a good question.
This is only going to make sense if we go back to the beginning.
To the time machine!
5 billion years ago, the solar system was just a giant cloud of gas and dust.
and gravity has began to pull it in causing it to collapse.
As the cloud got smaller, the particles of gas and dust started to bump into each other more often.
Over the course of about 50 million years, those collisions took their toll.
Most of the random up-and-down motions of the particles canceled out
leaving only the overall spin of the cloud.
It’s now what we call an “Accretion Disk,” which will eventually form the planets,
over the next few hundred million years.
Back to the lab!
So that’s it.
Conservation of momentum turns the cloud into a plane before the planets even form.
I have had it with mother [BEEP] planets in a mother [BEEP] plane!
Why wasn’t the Sun at the center of that cloud also a disk?
The gas and dust got too close too fast.
Remember, turning that cloud into a disk took millions of years.
By that time, 99.8% of the matter in that cloud had already fallen into the center.
The Sun was already on its way to forming long before it had a chance to flatten out.
If matter is very loosely packed, then one piece can travel a long way before it
runs into another piece.
That’s what it looks like in the accretion disk.
However, if matter is tightly packed and held in place by gravity, then
the pieces can’t get away from the collisions.
They’re stuck.
But that doesn’t mean they don’t try and that causes a net outward pressure in all directions,
which forms a sphere, not a disk.
But isn't it still trying to flatten out a little bit?
Right, so, like with most things, it's a spectrum.
There are two factors at work at the same time.
Outward pressure from the collisions and angular momentum from the spin.
If the matter is loose, angular momentum dominates and you get a disk.
If the matter is dense, outward pressure dominates and you get a sphere.
The angular momentum is always there though, so even the Earth and the Sun bulge at their
their equator a little bit.
Most asteroids and comets tend to be sort of in the awkward in-between.
Too dense to be a disk, but too light to be a sphere, so they turned out lumpy.
So, what’s the weirdest thing you’ve seen in the sky?
Please share in the comments.
Thanks for liking and sharing this video.
Please subscribe if you’d like to keep up with us.
And until next time, remember, it’s OK to be a little crazy.
In the last video, we learned how planes fly.
Comment response time! hisham borgol and FiVorT98 were both wondering
how planes actually move forward.
Good question!
Airplanes have very powerful engines that turn big turbines or propellers.
The blades of those engines pull the air backward so hard
that the plane responds by moving forward.
Also, conservation of momentum.
rotflmaopmpqxyz suggested that maybe Newton’s third law is a better explanation.
Well, yes, Newton’s third law is a valid explanation if you’re careful,
but I wouldn’t say it’s “better” per say.
I‘d say it’s about the same for the plane.
Technically, you can get conservation of momentum from Newton’s third law,
but you can also get Newton’s third law from conservation of momentum.
There is nothing that claim either one is more fundamental than the other.
It just comes down to how your brain works and what you’re used to.
When you do advanced physics a lot like I do
Things like Einstein’s relativity and quantum physics
you find that Newton’s laws aren’t nearly as useful as conservation laws,
so I’m just in the habit of thinking in terms of conservation laws.
Plus, I think they’re a little more elegant for deeper understanding.
Rogue Assassin Gaming is mind-blown by me saying air is a fluid.
Yes, air is a fluid.
In fact, any substance that is capable of flowing is called a fluid.
Basically, any substance whose molecules can move about freely.
That includes both liquids and gases. and, if you think about it, air and water
behave in a lot of the same ways.
Water is just so dense you can see it.
That’s all.
Joel Craig wants to know how to use science to take over the world.
I’ll never reveal my secrets!
[Maniacal Laughter]
Anyway, thanks for watching!
I’ll see you next time.