Why Does the Earth Rotate?

[Judi Lynn]

By Marcus Woo, Live Science Contributor | August 26, 2018 07:02am ET

Every day, the Earth spins once around its axis, making sunrises and sunsets a daily feature of life on the planet. It has done so since it formed 4.6 billion years ago, and it will continue to do so until the world ends — likely when the sun swells into a red giant star and swallows the planet. But why does it rotate at all?

The Earth formed out of a disk of gas and dust that swirled around the newborn sun. In this spinning disk, bits of dust and rock stuck together to form the Earth, according to Space.com, a sister site of Live Science. As it grew, space rocks continued colliding with the nascent planet, exerting forces that sent it spinning, explained Smadar Naoz, an astrophysicist at the University of California, Los Angeles. Because all the debris in the early solar system was rotating around the sun in roughly the same direction, the collisions also spun the Earth — and most everything else in the solar system — in that direction. [Photo Timeline How the Earth Formed]

But why was the solar system spinning in the first place? The sun, and the solar system, formed when a cloud of dust and gas collapsed due to its own weight. Most of the gas condensed to become the sun, while the remaining material went into the surrounding, planet-forming disk. Before it collapsed, the gas molecules and dust particles were moving all over the place, but at a certain point, some gas and dust happened to shift a bit more in one particular direction, setting its spin in motion. When the gas cloud then collapsed, the cloud's rotation sped up — just as figure skaters spin faster when they tuck their arms and legs in.

Because there isn't much in space to slow things down, once something starts rotating, it usually keeps going. The rotating baby solar system in this case had lots of what's called angular momentum, a quantity that describes the object's tendency to keep spinning. As a result, all the planets likely spun in the same direction when the solar system formed.

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[tblue37]

1. K&R. nt

[AJT]

2. Do all solar systems rotate in the same direction as ours?

[Duppers]

4. How could we tell? They might be upside down. 😜

Seriously, when you're looking at space, all directions are equivalent.

[AJT]

5. You mean people who live in the antipodes aren't upside down?

[Toorich]

3. If they are in the northern half of the universe....

...they spin one way. If they are in the southern part of the universe, they spin the other way.
Come back next week and we'll discuss gravity. heh heh heh

[ThoughtCriminal]

6. NASCAR in the Northern Hemisphere

maintains Earth's angular momentum, but probably causes more tornados.