I know caught in the suns gravity is what causes our yearly revolution , but what causes the earths rotation on it's axis ? our day is less than 24 hours. Saturns is a bit over 10 hours . but what keeps them spinning ?

one would think that the revolution around the sun would keep us one sided towards it . like our moon is with us. Our moon doesn't because of supposedly tidal forces and diametrical opposition. the side that is I guess more 'lopsided' for lack of a better term keeps it faced one way. but not all moons are like that ( most are ). Yet our earth isn't a perfect circle. so ................. why aren't we locked into position?

also - they know that the moon is moving away from the earth. in that same line of thinking is the earth moving away from the sun ?

ps -

I don't know where I heard this , it may not be true. but does one of the planets in our solar syster rotate on it's axis in the opposite direction of that of the other planets ?

doesn't anyone know ?

You know, I read your original posting a few times, I think it is a damn good question you have there!

I haven't even got a theory on it, let alone any answers, certainly food for thought though.

Maybe the moon works from our gravity whereas the Earth rotates upon its own. Regarding moving away, I didn't know this was happening, why didn't anyone tell me

Seriously though, is that true, about the moon moving away from the sun?

Nothing has to keep a planet spinning. The angular momentum of a system (part of which includes its spinning) is conserved, meaning it would take something to make it stop. So as long as they started spinning they'll continue to do so (and we can try and figure out what the initial conditions were when the planets formed to understand why things shook out the way they did). The Earth's spin is actually winding down by a very little bit because it's transferring angular momentum to the moon (which, in turn, gets further away as you pointed out). The total angular momentum of the Earth-Moon system, however, is staying constant.

We're not tidally locked to the sun because in order for that to happen some complicated mechanics have to play out, with bulges forming on a body and being dragged by the larger body, and so on. We've got enough distance from the sun that the conditions aren't quite right for that to occur.



Yes, Venus rotates "backwards" and Uranus rotates on its side, relative to the rest of the planets.

The solar system formed from dust and gas. Small centers of mass formed first, globbing together. Microgravity attracted the rest of the materials. Because they were all moving, they were drawn into circular orbits around the small mass centers - as opposed to just falling straight in - before they finally adhered to the centers. Because of this motion, along with the principle of conservation of angular momentum, the aggregate itself had to begin to spin as well. The rotations of the planets are the remnant of this original angular momentum.



The Moon did originally turn it's face away from us but tidal forces have locked it into it's current rotation, like you said.

BTW, the Moon does rotate. It turns one revolution on it's axis for every revolution it makes around the Earth. That's why we always see the same side.

The Earth - Sun system is vastly different. The moon is relatively close to the Earth so the effect occured there reasonably early (within a few billion years.) If the Solar system were to exist for long enough, the same might happen to the Earth with respect to the Sun. Unfortunately (or fortunately - depending on your point of view,) the Solar system almost certainly will not last long enough for this to happen.


The Moon is escaping the Earth at around an inch or two per year. It's one of the reasons scientists today postulate the impact theory of lunar formation because if it's true today it has had to have been happening all along. This fact brings to mind an impact theory because a "capture" theory involving a slow escape requires some pretty high odds. This and the fact that lunar rocks match well with what we suppose the Earth's mantle should be composed of indicates the likelihood that the Moon formed from the coalescence of ejecta after the Earth collided with a planet-sized body sometime in it's first billion years of existence as a planet.

I don't know about the Earth-Sun system, but I do know that the Earth will never escape the Sun. The Sun is destined to swallow the Earth once it runs out of hydrogen and starts burning helium.

Harte

Why does the Earth spin? Well, everything in the Solar System was born from a large rotating cloud of gas called the Solar Nebula, which at some point began to collapse under it's own gravity. As it contracted it became disc shaped with a dense bulge in the centre. That bulge in the centre formed a protostar (early Sun) while matter in the ("accretion") disc also began to contract in localized spots to form the protoplanets.

Image

All of the matter in the disc was rotating, and as it contracted to form the protoplanets it sped up because of something known as Conservation of Angular Momentum. The physical aspect of it is tough to explain (I'll try to afterwards if you want ), but imagine someone spinning while ice skating with their arms stretched out, as they pull their arms in to their body they would begin to spin faster. A rotating object will continue to rotate forever, unless an external force acts on it.

I believe Venus rotates on its axis in an opposite direction to every other planet, while Uranus and Pluto rotate sideways on their axes. This type of rotation is described as being "retrograde". Its cause isn't entirely understood yet but it's believed to be the result of colossal impacts with very large objects in the past.

The moon is gradually orbiting further and further from the Earth as a result of the energy it loses to tidal forces. There will eventually be a point where the Earth becomes tidally locked with the moon (just as how the moon is almost already locked with the Earth), at that point the moon will no longer recede. Not entirely sure why the Earth isn't subject to the same effect, though. Good question!

I just now ran into this -

I heard in the TV that moon is moving away from the earth towards the sun. Why is that happening? And when was this exactly discovered?

The Moon's orbit (its circular path around the Earth) is indeed getting larger, at a rate of about 3.8 centimeters per year. (The Moon's orbit has a radius of 384,000 km.) I wouldn't say that the Moon is getting closer to the Sun, specifically, though--it is getting farther from the Earth, so, when it's in the part of its orbit closest to the Sun, it's closer, but when it's in the part of its orbit farthest from the Sun, it's farther away.

The reason for the increase is that the Moon raises tides on the Earth. Because the side of the Earth that faces the Moon is closer, it feels a stronger pull of gravity than the center of the Earth. Similarly, the part of the Earth facing away from the Moon feels less gravity than the center of the Earth. This effect stretches the Earth a bit, making it a little bit oblong. We call the parts that stick out "tidal bulges." The actual solid body of the Earth is distorted a few centimeters, but the most noticable effect is the tides raised on the ocean.

Now, all mass exerts a gravitational force, and the tidal bulges on the Earth exert a gravitational pull on the Moon. Because the Earth rotates faster (once every 24 hours) than the Moon orbits (once every 27.3 days) the bulge tries to "speed up" the Moon, and pull it ahead in its orbit. The Moon is also pulling back on the tidal bulge of the Earth, slowing the Earth's rotation. Tidal friction, caused by the movement of the tidal bulge around the Earth, takes energy out of the Earth and puts it into the Moon's orbit, making the Moon's orbit bigger (but, a bit pardoxically, the Moon actually moves slower!).

The Earth's rotation is slowing down because of this. One hundred years from now, the day will be 2 milliseconds longer than it is now.

This same process took place billions of years ago--but the Moon was slowed down by the tides raised on it by the Earth. That's why the Moon always keeps the same face pointed toward the Earth. Because the Earth is so much larger than the Moon, this process, called tidal locking, took place very quickly, in a few tens of millions of years.

Many physicists considered the effects of tides on the Earth-Moon system. However, George Howard Darwin (Charles Darwin's son) was the first person to work out, in a mathematical way, how the Moon's orbit would evolve due to tidal friction, in the late 19th century. He is usually credited with the invention of the modern theory of tidal evolution.

So that's where the idea came from, but how was it first measured? The answer is quite complicated, but I've tried to give the best answer I can, based on a little research into the history of the question.

There are three ways for us to actually measure the effects of tidal friction.

* Measure the change in the length of the lunar month over time.

This can be accomplished by examining the thickness of tidal deposits preserved in rocks, called tidal rhythmites, which can be billions of years old, although measurements only exist for rhythmites that are 900 million years old. As far as I can find (I am not a geologist!) these measurements have only been done since the early 90's.

* Measure the change in the distance between the Earth and the Moon.

This is accomplished in modern times by bouncing lasers off reflectors left on the surface of the Moon by the Apollo astronauts. Less accurate measurements were obtained in the early 70's.

* Measure the change in the rotational period of the Earth over time.

Nowadays, the rotation of the Earth is measured using the Very Long Baseline Interferometry, a technique using many radio telescopes a great distance apart. With VLBI, the positions of quasars (tiny, distant, radio-bright objects) can be measured very accuarately. Since the rotating Earth carries the antennas along, these measurements can tell us the rotation speed of the Earth very accurately.

However, the change in the Earth's rotational period was first measured using eclipses, of all things. Astronomers who studied the timing of eclipses over many centuries found that the Moon seemed to be accelerating in its orbit, but what was actually happening was the the Earth's rotation was slowing down. The effect was first noticed by Edmund Halley in 1695, and first measured by Richard Dunthorne in 1748--though neither one really understood what they were seeing. I think this is the earliest discovery of the effect.

The Earth's rotation is slowing down because of this. One hundred years from now, the day will be 2 milliseconds longer than it is now. guess will have to reset out clocks ? lol

lots of good questions here however. thanks for the input.

http://curious.astro.cornell.edu/question.php?number=124

thanks raptor ! I thought I heard one of the planets rotated differently. I couldn't remember which.

I wonder what it would be like once the spinning has stopped. the very instant. maybe there would be a countdown like in NY times square !

It's Hesper or Mercury.
I think the rotation of Earth and Moon may be all explained by the self rotaiton of Sun. When the solar system first formed, by some reason the initial masses of celestial dust started to rotate by itselt. Then the core of this dust collapsed into the sun we now have and it kept rotating, so did the outer part of it, around the sun. And with various forces and inertias interacting with each other, layers of the outer dust split and began to self rotate. So began the rotation of the earth. In the same line of evolvement, the Moon began to self rotate.
Is that possible? I'm not an expert and I welcome any idea.

According to my physics professor, the Earth would eventually become tidally locked with the Sun if it wasn't for other external factors involved, such as the Moon's presence.

that was a very good question...
i also wanted to know this.

you may want to check again - it was about the moon moving away from the earth that would have the earth tidally locked. the moon moving away from the earth was the point.
The moon is gradually orbiting further and further from the Earth as a result of the energy it loses to tidal forces. There will eventually be a point where the Earth becomes tidally locked with the moon (just as how the moon is almost already locked with the Earth), at that point the moon will no longer recede. Not entirely sure why the Earth isn't subject to the same effect, though. Good question!

I remember a program last year (?) that remarked about the moon and it's moving away from the earth. that in the past , like as prehistoric man , the moon when in eclipse covered all of the sun. no corona showing. that it was that much closer to the earth.

here is a quick article on the moon with a bunch of little factoids -

http://www.astronomytoday.com/astronomy/earthmoon.html