Does the moon rotate, if not, why not?

[Steph]

That is not really odd, it is "physics" as explained by Steph. what is really odd though is that the Sun is as bigger than the Moon as It is farther, thus a perfect Eclips: seen from Earth, the Moon and the Sun have the same size. I have always find that very odd

Distance Earth - Sun = 149.6x10E6 km
Distance Earth - Moon = 380,000 km
Ratio = 390,000 (Rounded).

Diameter of the Moon = 3,470 km
Diameter of the Sun = 1.392E6 km
Ratio = 401

I don't see how the sun is as bigger than the moon as it is farther?

 

[warpus]

^^ What he means is that the moon appears to be just as large as the sun, when viewed from the Earth.

That is an amazing coincidence.

 

[Birdjaguar]

That is not really odd, it is "physics" as explained by Steph. what is really odd though is that the Sun is as bigger than the Moon as It is farther, thus a perfect Eclips: seen from Earth, the Moon and the Sun have the same size. I have always find that very odd

It's a "well designed" system. Perfect eclipses, full moons to coincide with monthly ovulation , tides to wash away sand castles and bring shells ashore. Moons to inspire poets:

The moon was a ghostly galleon, tossd upon a cloudly sea...

The thief left it behind, the moon at the window

 

[Leonel]

That's amazing how the face of the moon is always facing Earth! I wonder what happened to actually have that occur. Perhaps the moon really is Earth debris from a collision as the debris would be traveling at the same rotation as the Earth.

 

[MrCynical]

Distance Earth - Sun = 149.6x10E6 km
Distance Earth - Moon = 380,000 km
Ratio = 390,000 (Rounded).

Diameter of the Moon = 3,470 km
Diameter of the Sun = 1.392E6 km
Ratio = 401

I don't see how the sun is as bigger than the moon as it is farther?

He's referring to the fact that the moon and sun appear the same distance from Earth, so you're working out the wrong ratios.

Diameter of sun/Distance from Earth to sun = 1.392E6/149.6E6 = 9.30E-3

Diameter of moon/Distance from Earth to moon = 3,470/380,000 = 9.13E-3

Which is more or less the same, and is what makes total eclipses possible. As far as I know there isn't any special reason the ratios work out like this, it's just a coincidence.

 

[Birdjaguar]

As far as I know there isn't any special reason the ratios work out like this, it's just a coincidence.

It is so we can be amazed and wonder.

 

[Steph]

He's referring to the fact that the moon and sun appear the same distance from Earth, so you're working out the wrong ratios.

Diameter of sun/Distance from Earth to sun = 1.392E6/149.6E6 = 9.30E-3

Diameter of moon/Distance from Earth to moon = 3,470/380,000 = 9.13E-3

Which is more or less the same, and is what makes total eclipses possible. As far as I know there isn't any special reason the ratios work out like this, it's just a coincidence.

I know, it's just not what he said

 

[Steph]

That's amazing how the face of the moon is always facing Earth! I wonder what happened to actually have that occur. Perhaps the moon really is Earth debris from a collision as the debris would be traveling at the same rotation as the Earth.

It is NOT amazing, that's the case for most of the satellites in the solar system.

 

[Masquerouge]

What's amazing is the relative size of the Moon compared to Earth... I don't think any other planet has a moon so big relative to its size.

IIRC that was even a hint in an Asimov novel where they were trying to find Earth.

 

[Kan' Sharuminar]

What's amazing is the relative size of the Moon compared to Earth... I don't think any other planet has a moon so big relative to its size.

IIRC that was even a hint in an Asimov novel where they were trying to find Earth.

Pluto and Charon as well, I believe.

 

[The Great Apple]

EDIT: And TGA does a 1 hour crosspost... ooops.

Is Pluto really a planet though?

I think the other Asimov hint was the size of the gas giants, wasn't it? Not a very accurate guess unfortunetly.

 

[Sidhe]

He's referring to the fact that the moon and sun appear the same distance from Earth, so you're working out the wrong ratios.

Diameter of sun/Distance from Earth to sun = 1.392E6/149.6E6 = 9.30E-3

Diameter of moon/Distance from Earth to moon = 3,470/380,000 = 9.13E-3

Which is more or less the same, and is what makes total eclipses possible. As far as I know there isn't any special reason the ratios work out like this, it's just a coincidence.

Indeed at one time the moon was vastly larger in aspect than the sun and no eclipses were possible, as it slowly moves away it appears smaller and smaller so that logically at some point it will almost exactly equal the size of the sun and eclipses will occur, some day it will be so small that we will fail to notice the efect of an eclipse other than a small disc across it's face. It's not just coincidence it's inevitable coincidence.

http://en.wikipedia.org/wiki/Tidal_drag

Oddly enough I looked this up about two months ago when I realised I'd forgotten the exact mechanics of the OP's questions. Celsetial motion is rather precise, not easy to work out with complete accuracy but it all makes a beautiful cosmic sense. Hey who knows maybe one day this will be true of all physics, I'll be dead before then which I think is a good thing. Knowing how it all works would be so dull.

 

[blackheart]

Well, aren't all of you glad you're alive now and not in a billion years when the moon finally loses us?

 

[Kan' Sharuminar]

EDIT: And TGA does a 1 hour crosspost... ooops.

Is Pluto really a planet though?

I think the other Asimov hint was the size of the gas giants, wasn't it? Not a very accurate guess unfortunetly.

The other hint was the rings of Saturn, which in Asimov's universe was unique to the Solar System.

 

[Truronian]

IIRC, the moon was formed when an asteroid knocked a piece of the earth off when it was still molten. As the moon cooled, its rotational energy was wasted warping the moons cooling surface (its natural shape is an slight egg shape facing earth) to remain gravitational efficient. Eventaully, the moon solidified, and the rotation stopped (relative to earhts rotation) hence the moon's shape and fixed position.

Incidentally, when moons are not syncronised with their planet's rotation, this usually results in volcanic activity eg Io

 

[Cuivienen]

^^ What he means is that the moon appears to be just as large as the sun, when viewed from the Earth.

That is an amazing coincidence.

Which is untrue. The Sun appears to be smaller than the Moon in most instances, though it varies by the angle of inclination to the Earth (the Sun will appear larger near sunrise and sunset than near noon). During most solar eclipses, the Sun and much of the area directly around it is blocked out by the Moon, but the corona of the Sun (the "atmosphere" of the Sun seen only during eclipses) extends out far enough to be visible.

During an annular solar eclipse (which is quite rare), the Sun appears larger than the Moon and the edge of the Sun itself (rather than the corona) will be visible around the Moon.

 

[The Great Apple]

Which is untrue. The Sun appears to be smaller than the Moon in most instances, though it varies by the angle of inclination to the Earth (the Sun will appear larger near sunrise and sunset than near noon).

Doesn't the moon appear larger and moonrise and moonset as well?

 

[Steph]

This is because the angle at which you see the Moon through the atmosphere is "tangent", so the distance is not the same and you can get some magnifying glass effect, especially with some atmospheric condition (like humidity).

 

[sanabas]

Distance Earth - Sun = 149.6x10E6 km
Distance Earth - Moon = 380,000 km
Ratio = 390,000 (Rounded).

That should say 390:1, not 390000:1. Fairly close to 401:1

Incidentally, when moons are not syncronised with their planet's rotation, this usually results in volcanic activity eg Io

Heavy tidal activity in molten interior = lots of volcanic fun.

 

[Perfection]

Incidentally, when moons are not syncronised with their planet's rotation, this usually results in volcanic activity eg Io

Io is most definitely synchronized.