Isn't that true for all moons, though, simply because the radius of the orbit around the sun is much larger than the radius of the moon around the planet?
also, isn't the force ratio issue more an issue of the inverse square law than anything else?
From the point of view of the Sun, some satellites with short orbital periods might appear to move back and forth as they run around their planet. Earth's Moon, on the other hand, never moves backward from the point of view of the Sun.
That still wouldn't make the Moon a planet though.
the orbital period of the satellite isn't as important as the orbital velocity of the planet around the sun.
the earth goes around the sun at 29 785.8944 mps, so for a satellite to appear to stand still (from the sun's perspective) it needs that orbital speed (i'm assuming that everything orbits in the same plane to make things easier/cleaner).
using the equation v^2 = GM/R gives an orbital radius of(G = 6.673 x 10^-11 N m^2/kg^2 and M = 5.98x10^24 kg, 1N = 1kg * 1m /1s) 449, 777 m or 449.7 km. Of course, the radius of the earth is 6.3 million meters (6300 km), so this isn't exactly possible.
the only way for a satellite orbiting a planet to appear to move backwards with respect to the thing the planet orbits is for the satellite to have a faster orbital velocity than the planet's orbital velocity.
No. If the Earth's mass were to vanish, the Moon would continue to orbit the Sun. It would be a bit more wobbly, but the Earth is not an essential part of the system.
If the same happened to Jupiter, all of those moons would fly out of of the solar system. (Or at least go cometary.) None of the orbits would survive.
That has to do with the distance between the sun and Jupiter not just Jupiter's mass. http://en.wikipedia.org/wiki/Deimos_%28moon%29 Deimos would continue to orbit the sun in much the same way that the moon would if it's planet disappeared. (Moon: 1.022 km/s, Deimos: 1.3km/s, Callisto's 8.204 km/s. Earth 29.78 km/s, Mars 24.077 km/s, and Jupiter 13.07 km/s)
Edit: http://en.wikipedia.org/wiki/Escape_velocity To escape from the suns orbit at Jupiter's distance from the sun takes 18.5 km/s vs Mars orbit's 34.1 km/s, or the Earth's orbit 42.1 km/s.
PS: The moon was the original example of 'moon' so it's a moon by definition. Any definition that does not include it must be describing something other than a 'moon'.
Your Deimos (and Moon) velocities are off, as those are velocities relative to Mars and Earth comparatively. The real question is, does 24.1km/s +- 1.3km/s keep Deimos in orbit without Mars. 5% change in velocity will probably knock it a bit out of whack, but I am not doing the perigee/apogee calculations right now.
PS, The Earth was the original example of 'flat' and nothing is ever allowed to change as we gain better understanding.
Everything's orbital velocity was taken relative to what they orbit. My point is if you take Jupiter and +/- the moon's orbital velocity you get a more extreme orbits than you do with Mars +/- Deimos. So the new orbits say just as much about how far they are from the sun vs what they orbit.
PS: The Earth is not the original definition of flat.
No, you took the Moon's velocity relative to the Earth. The Moon orbits the Sun and its velocity relative to Earth is only useful for astrology purposes.
If you want to use the deepest gravity well then the Moon orbits the black hole in the center of the Milky Way Galaxy (plus the matter closer the the center). Orbital velocity 216 kilometers per second around Milky way vs 42.1 +/- 1 km/s around the sun and earth.
However, when you look at the actual accelerations involved the moon is much more attracted to the earth (by over 100x) than it is to the sun or the center of the Galaxy. Which is why the moon is tidally locked with the earth and not the sun.
PS: All of these still don't add up to the 583km/s velocity relative to the CBR.
> However, when you look at the actual accelerations involved the moon is much more attracted to the earth (by over 100x) than it is to the sun
Your "over 100x" figure is entirely made up. The correct answer is 0.46.
Depth of the well does not matter, it is the steepness of the well. In other words, what is pulling the hardest on the Moon. The Sun pulls twice as hard as the Earth, so there is a compelling argument that the Sun is the Moon's primary.
The black hole at the center of the Milky Way is (rounding up for your benefit) 4 million solar masses and 27000 ly away. But that inverse square law really hurts and the Sun's gravitational force is 733e15 times stronger than the black hole's.
Let's step it up and include all 10 billion solar masses in the center. The Sun is still ahead by a factor of 290 trillion. The galactic core has almost no effect on the solar system, so it is silly to claim that any planetary body orbits the core.
Regarding tidal lock, the force of tidal lock is (more or less) proportionate to gravitational force * angular velocity. While the Earth's gravitational force on the Moon is half as strong as the Sun's, the relative angular velocity is 12 times faster. So the Earth's tidal forces on the Moon are six times stronger than those of the Sun. Naturally, the Moon is tidal locked to the Earth.
If Jupiter were to orbit the sun at the same distance of the earth, what would happen to the orbits of the moons if its mass suddenly disappeared? Would they still be cometary (at the least) or would they settle into a planetary orbit?
At 1AU, orbital velocity is 42.3 km/s. Io does 17.3 km/s relative to Jupiter. Io would be gone. Calliso does 8.2 km/s and I highly suspect that would be too fast to maintain a planetary orbit at 1AU.
The orbital velocity of Earth is the escape velocity of the solar system, from Earth (42.1 km/s). Fun fact, this means that if we ever wanted to dispose of nuclear waste by dumping it in a star, we'd need much less rocket fuel to hit Alpha Centauri than the Sun.
Jupiter has an orbital velocity of only 13.7 km/s, so even if Io is going the right direction and all the elliptical planes are parallel, isn't that still just a max orbital velocity of ~40 km/s, which is slow enough for orbit at 1AU?
It'd be interesting to see what happens at Jupiter's orbit, thouh. Does Io always leave? What about Callisto? It seems like there would be a large part of their orbit that would send them off into cometary orbits (or worse) depending on what direction they are going when scotty beams jupiter aboard the enterprise.
Can you explain (or link to) "Fun fact, this means that if we ever wanted to dispose of nuclear waste by dumping it in a star, we'd need much less rocket fuel to hit Alpha Centauri than the Sun."
It's not making much sense to my tired mind today.
It takes less energy to accelerate an object away from both the Earth and sun (assuming your launch pad is on an appropriate spot on the Earth surface), than to accelerate an object away from the Earth but into the sun without just getting the object stuck in an orbit like Venus or Mercury.
I don't see how this and Kepler's laws fit together. The moon's mass is significantly different from the earth. How could the moon have the same orbit as the earth if the earth wasn't there?
also, isn't the force ratio issue more an issue of the inverse square law than anything else?