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Hurricane Andres and tropical storm Blanca swirl off the coast of Baja California, Mexico.
We're smack in the middle of hurricane season, which means that many tropical vacation plans are about to be ruined by howling winds and bendy palm trees.Hurricanes are called many different things - typhoons, cyclones, tropical cyclones - but they all have one thing in common: they spin.
If you've ever seen one of those swirly animations of a hurricane creeping from the ocean before it makes its frightening debut on land, you know what I'm talking about.
Fascinatingly, the direction of that spin depends on what hemisphere of the world the hurricane is brewing in.
A hurricane's spin and the spin's direction is determined by a super-powerful phenomenon called the "Coriolis effect." It causes the path of fluids - everything from particles in the air to currents in the ocean - to curve as they travel across and over Earth's surfaces.
The physics behind this natural phenomenon can be mind-numbingly complicated, but this YouTube video by Nova PBS does a great job of explaining things. Here's how it works:
Cold, dense air at the north and south poles is really heavy so it falls to the ground and is pushed down toward the equator. Warmer, lighter air near the equator is less dense and tends to rise and move pole-ward. These movements create natural currents of air that flow up and down from the areas of high pressure at the poles to the lower pressure areas at the equator.
Because the globe is a sphere, though, these currents don't stay on a straight path.
During the 24 hours Earth takes to make one revolution, points along the equator (and therefore the air above them) have to move much faster than areas near the poles, because they have much farther to travel during the same amount of time.
You can see that in this gif below:
So, as Earth rotates, it sweeps these air currents off the straight vertical line between the equator and poles, curving their movement.
This causes the air to be pushed to the right as it travels northward in the northern hemisphere.
And when traveling from the equator to the south, the air curves to the left.
This creates a circular spinning pattern as air travels up and down from areas of high pressure to low pressure.
That's why hurricanes originating in the northern hemisphere rotate counterclockwise.
And those developing in the southern hemisphere spin in a clockwise direction.
For further explanation on how the effect influences hurricanes, check out the full video here:
And FYI, this phenomenon doesn't explain the circular direction that water travels in your toilet bowl after you flush. A toilet bowl is too small to be affected by such a grand process.