Earth's Moon
- Thread starter Orleander
- Start date
There is evidence that the Moon is still slowly moving away from Earth. What amazes me is the speculation of how the Sun is 400 times larger than the Moon, but the Moon is 400 times closer to Earth than the Sun, accounting for some spectacular eclipses. Though I don't know about a second moon.
Objects as local as the moon certainly do not move away due to expansion of the universe.
so our moon has always been exactly the same distance away, just like we have always been exactly the same distance from the sun? So that would be proof that we have never had another moon right? (sorry Oli, that 'moon' doesn't count
)so our moon has always been exactly the same distance away, just like we have always been exactly the same distance from the sun? So that would be proof that we have never had another moon right? (sorry Oli, that 'moon' doesn't count
No I'm not saying that, I'm just saying that because of gravity even the galaxy isn't even moving apart due to expansion.
Asking whether we never had more than one satellites is pointless.
How big? How long for?Is the Planetesimal stage of the earth included?
so our moon has always been exactly the same distance away, just like we have always been exactly the same distance from the sun? So that would be proof that we have never had another moon right? (sorry Oli, that 'moon' doesn't count
No. Due to friction the moon is constantly moving away from Earth. Before it was closer to Earth than now, and on Earth the moon influence was much stronger. We are the lucky ones to see the moon and the sun with the same angular sizes. Later the moon will be further, and Earth will be more susceptible to killer asteroids.
so eventually we will have no tides?
How will it be ejected? Will it just go floating off or will another planet grab it?
Not correct.
The sun already has greater gravitational effect (stronger force) on the moon than the Earth does. (If you do not believe, calculated the relative Mass/separations^2 ratios for both sun and Earth (except for factor "G", the gravitational force at the moon).
In fact, the moon is now going arround the sun in essentially the same elliptic orbit as the Earth is. I.e. The moon only appears to be going around the Earth when viewed from the Earth. In fact, it is always with a trajectory that is curving towards the sun. Never is the moon on a trajectory that is convex towards the sun (as you would expect it to be if it were going around the Earth like most man made satellites are).
If the Earth were magically removed there would be very little difference in the moon's orbit about the sun. That orbit now has slight
"wobbles" about the true ellipse, which are caused by the relatively weak gravity from Earth and of course if Earth disappeared or had no gravity, they would cease to exist, but viewed from Mars, it would not be a noticable change in the moons orbit if the Earth had zero gravity. Earth does NOT control the moon. Really Earth does not have a natural moon, but is the larger of two interacting masses that co-orbit the sun.
Thread is badly named, reflecting this common erroneous POV. Should be called "Sun's planatoid near Earth" or something like that.
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I agree the point where the influence of the other objects becomes more than that of Earth would not necessarily decide whether the moon is a sattellite of Earth or not. Wikipedia says that the Moon will continue to move slowly away from the Earth until the tidal effects between the two are no longer of significance, whereupon the Moon's orbit will stabilise.
It used to be closer than it is today, but that has nothing to do with the expanding universe. The expansion of the universe essentially doesn't affect anything in our galaxy, or anything in our solar system. Local gravitational effects dominate there.
During the formation of the solar system, there were probably hundreds of moons flying around. Some ended up as part of the Earth; some formed our current Moon; some ended up in orbits completely different from the Earth; some were swept up by Jupiter. Some ended up as asteroids.
I don't see how you can count on that. It depends on what theory you hold to, but if space itself is expanding, stretching out, I think that while the moon doesn't actually "move" further away the space between the Earth and the moon becomes longer.
:roflmao:
No it depends on whether you adhere to data like redshift and flux of stars in our vicinity, which show no trends of recession.
To be honest any so called theory you say has an object as close as moon receding from the earth oposing gravity confinment should be grounds for the author to be commited.
The friction explanation is the right answer.