Take the 2-minute tour ×
Earth Science Stack Exchange is a question and answer site for those interested in the geology, meteorology, oceanography, and environmental sciences. It's 100% free, no registration required.

Why does earth rotate in a clockwise direction? Did a large meteor collide with earth causing earth to rotate? If that is what happened, could another, larger meteor cause earth to reverse its rotation?

share|improve this question
8  
The earth spins clockwise because "clockwise" was first defined as the direction the shadow on a sundial moves, which is caused by the Earth's rotation. ;) –  Mason Wheeler May 1 at 0:06
10  
Also, we in southern hemisphere know that all you northern hemispheries are wrong - the earth spins anti-clockwise. We just have to put up with your clocks because of cultural imperialism and all that :P –  naught101 May 1 at 6:34

2 Answers 2

up vote 10 down vote accepted

Earth's Spin

Earth rotating clockwise is the result of a chain reaction that started when Earth's star formed as the result gas clouds collapsing. During the collapse of the gas, one direction was shorter and a disc formed. Due to the law of conservation of angular momentum, the disc gained an overall spin, which was passed to all the objects of notable mass within its solar system; these objects are commonly known as planets. As a result, all plants within a given solar system have the same spin as the star in their solar system to start.

Might be worth noting that all rotating bodies that rotate clockwise when viewed from the southern hemisphere rotate and counter-clockwise when viewed from the northern hemisphere. Also, since the Sun is not solid on the surface, it does not rotate as a solid body; meaning it rotates faster at its equator and slower at its poles.

Earth's Axis

As for the reasoning behind, the axis of the rotation, as pointed out in other answers, this is the result of Earth's past impacts with objects of enough mass to produce the shift from a zero offset from the stars axis, to the current axis of the rotation. Future impacts would be able to change the rotation.

Current Axis of the Planets in Earth's solar system

enter image description here

share|improve this answer
2  
NB some planets do exhibit retrograde spin - even within our solar system. Venus is a counter-example; Uranus is ambiguous. Source. –  kaberett Apr 30 at 21:46
    
+1 @kaberett: Awesome, thanks; reviewed another source - "Why Venus Spins the Wrong Way" - and updated the answer too. –  blunders Apr 30 at 21:56
    
The source for the opening paragraph runs counter to current theory of terrestrial planet formation. It ignores that angular momentum is not conserved thanks to gravitational torques and collisions. Asteroids are also subject to the YORP effect. In fact, the obliquities of the asteroids is pretty close to randomly distributed. –  David Hammen May 1 at 14:44
    
@DavidHammen: Do you have sources for any of your claims to review? Thanks! –  blunders May 1 at 14:50
    
@blunders - Lhotka, Souchay, and Shahsavari Obliquity, precession rate, and nutation coefficients for a set of 100 asteroids, A&A 556:A8 (2013) Those 100 asteroids have random obliquties. Obliquity ranges from 0 to 180 degrees. Slivan, Spin vector alignment of Koronis family asteroids, Nature 419:49 (2002). Most members of this family of asteroids have retrograde rotation. –  David Hammen May 1 at 15:02

If you ascribe to the giant impact hypothesis, which most scientists do, whatever rotation the Earth had prior to the formation of the Moon was lost thanks to that 'giant impact'. That was a massive impact involving a Mars-sized body colliding with the proto-Earth. A "little" impact wouldn't change the Earth's rotation by much at all. Note very well: Something that could entirely wipe out life as we know it would still be "little" in this regard. Another big oblique whack by a Mars-sized body would be needed to make a sizable dent in the Earth's rotation axis.

If you look at the nine eight planets, it's only Jupiter that reliably retains its primordial rotation. Whatever rotation rate / rotation axis Mercury and Venus had in the distant past has been wiped out thanks to tidal interactions between those planets, the Sun, and Jupiter (a.k.a. the 600 pound gorilla). Mars' rotation is notoriously chaotic. Uranus has been tilted by ~90 degrees by something, either a big whack or (once again) tidal interactions. Neptune and Saturn have obliquities of about 30 degrees. Those deviations may be a result of tidal interactions, or maybe of a lesser whack. Scientists don't know. There are lots of different hypotheses, but all have problems and none has taken hold yet.

The Earth? Whatever formed the Moon, whether by giant impact or something else, it almost certainly wreaked havoc with the Earth's primordial rotation.

share|improve this answer
2  
"If you look at the (nine) eight planets" Ya, I'm still really missing Pluto too. :'( –  Azzie Rogers May 1 at 14:35

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.