Why Does the Earth Spin the Way it Does?

The earth rotates west-to-east; counter clockwise looking from the north pole.  Of course, some alien flying through space could easily approach the solar system from our “south" pole, and see us spinning clockwise.  Nevertheless, why do we spin the way we do?  Why not spin east-to-west, or why spin at all?  

It turns out, it’s quite simple:

• A cloud of cosmic stuff 4.5 billions years ago gets hit by something; perhaps a supernova

• The cosmic stuff collapses into itself due to strong gravitational pull

• To conserve the energy, the cloud begins to spin (called angular momentum); the smaller the cloud gets, the faster it spins (e.g. a skater pulling arms inward to speed up the spin)

• The cosmic stuff starts to combine; collide; and stretch to eventually form the solar system

• With no resistance, the solar system, including the earth, continues to spin (“…an object in motion tends to stay in motion”).  However, the earth’s spin is slowing due to the moon’s pull.  Millions of years ago, the earth took only 22 hours to complete a rotation…and a million years from now, it will eventually take 26 hours.

• Don't like the way we spin? Try moving to Venus - it takes 243 earth days for Venus to complete one rotation...and it spins in the opposite direction!  Or perhaps Uranus  - - it rotates on it’s side (the axis pointing towards the sun).

Well, maybe it's not all that simple…but it puts an interesting spin in things, doesn't it?


Read more at: 

http://phys.org/news105637304.html#jCp
http://spaceplace.nasa.gov/review/dr-marc-earth/earth-rotation.html
http://phys.org/news105637304.html

http://www.universetoday.com/14491/why-does-the-earth-rotate/