<p>Any body with an irregular mass distribution will experience those wobblings. And more if it is not just irregular but fluid.</p>

CC BY-SA 3.0
2013-12-11T11:11:53.250Z
I didn't even know that bodies with an irregular mass wouldn't have a constant rotation speed. But I didn't understand your second sentence, care to explain?
Fabinout
CC BY-SA 3.0
2013-12-11T11:19:00.387Z
@Fabinout fluid bodies like Earth or a balloon filled with a mixture of water and oil will undergo changes in their mass distribution, and any mass redistribution will change rotational speed due to constant angular momentum.
Envite
CC BY-SA 3.0
2013-12-11T11:21:35.100Z
Oh yeah, thanks that makes sense, even more since you edited your second sentence.
Fabinout
CC BY-SA 3.0
2013-12-11T11:22:40.950Z
Yes, I realized the typo
Envite
CC BY-SA 3.0
2013-12-11T11:05:51.050Z
2013-12-11T11:19:09.450Z
2013-12-11T11:19:09.450Z
Envite
<p><a href="http://en.wikipedia.org/wiki/Earth%27s_rotation#Changes_in_rotation" rel="nofollow">Wikipedia's article on Earth's Rotation</a> proposes an example:</p>

<blockquote>
  <p>By affecting Earths moment of inertia, some large scale events, such
  as the 2004 Indian Ocean earthquake, have caused the rotation to speed
  up.</p>
</blockquote>

<p>Another one is seen in <a href="http://io9.com/5884476/shifting-ocean-currents-can-actually-speed-up-earths-rotation" rel="nofollow">Shifting ocean currents can (and do) actually speed up Earth's rotation</a> where it goes on to say:</p>

<blockquote>
  <p>Back in November 2009, something strange happened the Southern Ocean.
  The Antarctic Circumpolar Current suddenly slowed down. The change in
  current was extreme enough to throw off the planet's angular momentum,
  and so to compensate, the Earth sped up its rotation. For about two
  weeks, the days were a tenth of a millisecond shorter than they should
  be. Then, with just as little warning, the current returned to its
  normal speed, and the Earth slowed back down.</p>
</blockquote>

<p>This is understandable since currents affect the amount of water on any given place and thus the distribution of mass on earth. </p>

CC BY-SA 3.0
2013-12-11T15:02:13.373Z
It is not the amount of water, but the fact that water is moving around the Antarctica and has its own angular momentum. Total angular momentum of the Earth is conserved, so if you speed the water flowing in the same direction as the planet rotates, the planet slows down.
Envite
CC BY-SA 3.0
2013-12-11T14:50:20.377Z
2013-12-11T14:50:20.377Z
Eduardo Serra
<p>To complete Envite's answer, I would point that you can easily experience that irregularity yourself.</p>

<p>Take a fresh egg. Rotate it on a table. Stop it briefly and release it.</p>

<p>The egg will continue to rotate irregularly because of the fluids moving inside. </p>

<p>Since the egg is not a mathematic ball, and the fluids inside have several phases : yellow part, white part and gaz, the forces inside are complex, so the rotation is irregular.</p>

<p>Moreover I think the Moon is not helping with the regularity of fluids moving (cf sea tides).</p>

CC BY-SA 3.0
2013-12-11T11:32:26.840Z
2013-12-11T11:32:26.840Z
Thibault
<p>It is known as a fact that Earth's rotation is slowing every year, that's why we sometimes have 61 seconds long minutes.</p>

<p>In the Java documentation of Time : <a href="http://docs.oracle.com/javase/7/docs/api/java/util/Date.html" rel="noreferrer">http://docs.oracle.com/javase/7/docs/api/java/util/Date.html</a> , it is said :</p>

<blockquote>
  <p>Some computer standards are defined in terms of Greenwich mean time
  (GMT), which is equivalent to universal time (UT). GMT is the "civil"
  name for the standard; UT is the "scientific" name for the same
  standard. The distinction between UTC and UT is that UTC is based on
  an atomic clock and UT is based on astronomical observations, which
  for all practical purposes is an invisibly fine hair to split. Because
  <strong>the earth's rotation is not uniform (it slows down and speeds up in
  complicated ways)</strong>, UT does not always flow uniformly. Leap seconds are
  introduced as needed into UTC so as to keep UTC within 0.9 seconds of
  UT1, which is a version of UT with certain corrections applied. There
  are other time and date systems as well; for example, the time scale
  used by the satellite-based global positioning system (GPS) is
  synchronized to UTC but is not adjusted for leap seconds.  </p>
</blockquote>

<p>Why is that so? How can this occur?</p>

CC BY-SA 3.0
2013-12-12T14:56:36.290Z
Fabinout, unfortunately we don't cover questions of Earth science here. If you feel the answers you have gotten so far have been incomplete in any way, you are welcome to ask this question on Physics.SE or wait for the new Geoscience proposal to come out to beta!
called2voyage
CC BY-SA 3.0
2013-12-12T15:06:26.653Z
@called2voyage It's ok, I just thought the answer was astronomical, and it wasn't, my bad.
Fabinout
<earth><rotation>
How can the Earth's rotation speed up?
Fabinout
# How can the Earth's rotation speed up?

(Asked by: username_0 on 2013-12-11)

It is known as a fact that Earth's rotation is slowing every year, that's why we sometimes have 61 seconds long minutes.

In the Java documentation of Time : <http://docs.oracle.com/javase/7/docs/api/java/util/Date.html> , it is said :

> Some computer standards are defined in terms of Greenwich mean time
> (GMT), which is equivalent to universal time (UT). GMT is the "civil"
> name for the standard; UT is the "scientific" name for the same
> standard. The distinction between UTC and UT is that UTC is based on
> an atomic clock and UT is based on astronomical observations, which
> for all practical purposes is an invisibly fine hair to split. Because
> **the earth's rotation is not uniform (it slows down and speeds up in
> complicated ways)**, UT does not always flow uniformly. Leap seconds are
> introduced as needed into UTC so as to keep UTC within 0.9 seconds of
> UT1, which is a version of UT with certain corrections applied. There
> are other time and date systems as well; for example, the time scale
> used by the satellite-based global positioning system (GPS) is
> synchronized to UTC but is not adjusted for leap seconds.

Why is that so? How can this occur?

**Tags:** earth, rotation
> **Comments:**
> **username_1**: Fabinout, unfortunately we don't cover questions of Earth science here. If you feel the answers you have gotten so far have been incomplete in any way, you are welcome to ask this question on Physics.SE or wait for the new Geoscience proposal to come out to beta!  
> **username_0**: @called2voyage It's ok, I just thought the answer was astronomical, and it wasn't, my bad.  

---

## 3 answers

### Answer by username_2 on 2013-12-11. Score: 3 | Accepted answer

Any body with an irregular mass distribution will experience those wobblings. And more if it is not just irregular but fluid.

> **Comments:**
> **username_0**: I didn't even know that bodies with an irregular mass wouldn't have a constant rotation speed. But I didn't understand your second sentence, care to explain?  
> **username_2**: @Fabinout fluid bodies like Earth or a balloon filled with a mixture of water and oil will undergo changes in their mass distribution, and any mass redistribution will change rotational speed due to constant angular momentum.  
> **username_0**: Oh yeah, thanks that makes sense, even more since you edited your second sentence.  
> **username_2**: Yes, I realized the typo  

---

### Answer by username_3 on 2013-12-11. Score: 3

[Wikipedia's article on Earth's Rotation](http://en.wikipedia.org/wiki/Earth%27s_rotation#Changes_in_rotation) proposes an example:

> By affecting Earths moment of inertia, some large scale events, such
> as the 2004 Indian Ocean earthquake, have caused the rotation to speed
> up.

Another one is seen in [Shifting ocean currents can (and do) actually speed up Earth's rotation](http://io9.com/5884476/shifting-ocean-currents-can-actually-speed-up-earths-rotation) where it goes on to say:

> Back in November 2009, something strange happened the Southern Ocean.
> The Antarctic Circumpolar Current suddenly slowed down. The change in
> current was extreme enough to throw off the planet's angular momentum,
> and so to compensate, the Earth sped up its rotation. For about two
> weeks, the days were a tenth of a millisecond shorter than they should
> be. Then, with just as little warning, the current returned to its
> normal speed, and the Earth slowed back down.

This is understandable since currents affect the amount of water on any given place and thus the distribution of mass on earth.

> **Comments:**
> **username_2**: It is not the amount of water, but the fact that water is moving around the Antarctica and has its own angular momentum. Total angular momentum of the Earth is conserved, so if you speed the water flowing in the same direction as the planet rotates, the planet slows down.  

---

### Answer by username_4 on 2013-12-11. Score: 3

To complete Envite's answer, I would point that you can easily experience that irregularity yourself.

Take a fresh egg. Rotate it on a table. Stop it briefly and release it.

The egg will continue to rotate irregularly because of the fluids moving inside.

Since the egg is not a mathematic ball, and the fluids inside have several phases : yellow part, white part and gaz, the forces inside are complex, so the rotation is irregular.

Moreover I think the Moon is not helping with the regularity of fluids moving (cf sea tides).


---

