Darren New <dne### [at] sanrrcom> wrote:
> Warp wrote:
> >   Interesting tidbit: Did you know that Moon's orbit around the Sun is
> > completely convex? (In other words, the curvature of the orbit never
> > changes sign.)

> Yes, that's what I'd read about. In essence, it's orbiting the sun as it 
> wobbles back and forth across the earth's orbit, rather than actually 
> orbiting the earth. That's why I thought we might be much closer to losing it.

  "Rather than actually orbiting the Earth" is incorrect. It *is* orbiting
the Earth. The Earth-Moon system is orbiting the Sun. Ergo the Moon is
*also* orbiting the Sun. In other words, the Moon is orbiting both.

  The orbital period of the Moon around the Earth is so slow that if we
trace the Moon's orbit around the Sun, it actually results in a completely
convex shape. However, that's more a curiosity than anything else. It
doesn't mean it's not "actually orbiting the Earth".

-- 
                                                          - Warp

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Warp wrote:
> doesn't mean it's not "actually orbiting the Earth".

Hmmmm.   OK.   I don't feel like doing the math, but I suspect you're right. 
:-)  Maybe at some point I'll figure out how much the sun attracts the moon 
vs the earth.

-- 
   Darren New, San Diego CA, USA (PST)
   I ordered stamps from Zazzle that read "Place Stamp Here".

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Darren New <dne### [at] sanrrcom> wrote:
> I had read in a reliable source that the moon is actually more attracted to 
> the Sun than the Earth when it's at eclipse, but I never did the math 
> myself, and I'm too lazy to look at the math here to see if that's 
> sufficient to disrupt the orbit anyway. :-)

  As I have said many times already, the Sun's gravitational pull being
stronger than the Earth's is inconsequential. The Sun's gravitation is
affecting *both* the Moon and the Earth at the same time, as a whole.
They are both "falling" at the same rate. Thus it doesn't really matter
what this rate actually is (at least not at Earth's altitude).

  Think of it like this: At midday the Sun's gravitation effect on *you*
is stronger than the Earth's. However, that doesn't mean you are going to
be pulled out of Earth. (The reason is that the same gravitation is *also*
affecting the Earth.) Easier to understand it like this?

-- 
                                                          - Warp

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Warp <war### [at] tagpovrayorg> wrote:
>   Think of it like this: At midday the Sun's gravitation effect on *you*
> is stronger than the Earth's. However, that doesn't mean you are going to
> be pulled out of Earth. (The reason is that the same gravitation is *also*
> affecting the Earth.) Easier to understand it like this?

  (Ok, I must confess I actually don't know if that's true because I haven't
done the math nor seen others' results on that. However, it could be true
and it wouldn't change anything.)

-- 
                                                          - Warp

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Darren New <dne### [at] sanrrcom> wrote:
> Warp wrote:
> > doesn't mean it's not "actually orbiting the Earth".

> Hmmmm.   OK.   I don't feel like doing the math, but I suspect you're right. 
> :-)  Maybe at some point I'll figure out how much the sun attracts the moon 
> vs the earth.

  I don't really understand why you are so fixated about this Sun vs Earth
gravitation thing.

  The Sun is affecting *both* the Earth and the Moon, not the Moon alone.
It's not like the Sun and the Earth were competing with each other to see
which one gets to pull the Moon. It doesn't matter if the Sun's gravitation
is stronger than the Earth's. It makes little difference.

-- 
                                                          - Warp

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Warp wrote:
> It doesn't matter if the Sun's gravitation is stronger than the Earth's. 

I'm just having trouble figuring out *why* it doesn't matter. :-)

-- 
   Darren New, San Diego CA, USA (PST)
   I ordered stamps from Zazzle that read "Place Stamp Here".

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Warp wrote:
>   Think of it like this: At midday the Sun's gravitation effect on *you*
> is stronger than the Earth's. 

I don't think it is, tho.

> However, that doesn't mean you are going to be pulled out of Earth. 

If you go to where the moon's gravity exactly matches the earth's gravity, 
in space between the two, you'll not be attracted to either one, right? If 
you're ten miles closer to the moon, eventually you'll fall onto the moon. 
If you're ten miles closer to the earth, eventually you'll fall onto the earth.

>(The reason is that the same gravitation is *also*
> affecting the Earth.) Easier to understand it like this?

I can see where the mechanics of the orbits would have an effect on it. 
Maybe I just need more coffee. Obviously the Sun is not wresting the Moon 
away from the Earth, so I'll just have to let it perk a while and see if my 
hind-brain can figure out an intuitive-for-me way of understanding it.

-- 
   Darren New, San Diego CA, USA (PST)
   I ordered stamps from Zazzle that read "Place Stamp Here".

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On 09/20/09 16:05, Darren New wrote:
> If you go to where the moon's gravity exactly matches the earth's
> gravity, in space between the two, you'll not be attracted to either
> one, right? If you're ten miles closer to the moon, eventually you'll
> fall onto the moon. If you're ten miles closer to the earth, eventually
> you'll fall onto the earth.

	That's only if you assume no transverse velocity - which is not the 
case for the moon.


-- 
"Eureka!" said Archimedes to the skunk.

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On 09/20/09 12:42, Darren New wrote:
> If the moon drifts far enough from the earth, the gravity from the sun
> will be stronger than the gravity of the earth, so something strange is
> likely to happen.

	Actually, it's quite possible that the gravity of the sun is already 
greater. At the very least, they're of the same order of magnitude.


-- 
"Eureka!" said Archimedes to the skunk.

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Neeum Zawan escreveu:
> On 09/19/09 13:49, Warp wrote:
>>    Maybe, but let's not forget what the F in SF stands for.
> 
>     That F may encompass the whole concept of alien life, if you want to 
> be picky...

Life itself is so unlikely that it may well be we're all living a big 
fiction... :P

-- 
a game sig: http://tinyurl.com/d3rxz9

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