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Our moon has been slowly drifting away from Earth over the past 2.5B yrs

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Re: Our moon has been slowly drifting away from Earth over the past 2.5B yrs

#51

Post by [deleted] »

chowells wrote: post #19
FiatLuxDave wrote: post #10

Earlier quoted context omitted.

Sure. The earth is spinning faster than the the moon is going around the earth (earth rotates in one day, the moon goes around in about a month). When the tides transfer energy and momentum to the moon from the earth's spin, it slows down the earth's spin and gives the moon more energy. This moves the moon to a higher orbit, so it moves a bit farther away from us. The source of energy for the whole process is the ear…

If the moon's orbit is increasing in radius, doesn't that mean its orbital velocity is decreasing? Which way is energy being transferred? This stuff confuses me.

[deleted]

Re: Our moon has been slowly drifting away from Earth over the past 2.5B yrs

#52

Post by doubleunplussed »

egberts1 wrote: post #48

Despite the rapid devolvement of the Moon’s rotational at its own polar axis (to a point of having one face of the Moon being tidal locked toward Earth) since its birthing from Earth, I remain curious about the breakage of such tidal locking as Moon’s orbit dramatically continues to expand.

Nah it won't. The timescale for it to lock is much faster than anything else - it'll stay locked the whole time.

Re: Our moon has been slowly drifting away from Earth over the past 2.5B yrs

#53

Post by robertlagrant »

aussieshibe wrote: post #21
redact207 wrote: post #12

Earlier quoted context omitted.

If the moon wasn't drifting away and was in a static orbit, would the Earth's rotation slow and the moon's orbit speed up to the point where they're in sync?

Fair warning: everything I know about orbital mechanics is from Kerbal Space Program. The moon cannot orbit at a higher speed while keeping the same semi-major axis (average distance to the orbital centre of mass). If you suddenly doubled the orbital speed of the moon right now, the apoapsis (the highest point in its orbit relative to the orbital centre of mass) would increase significantly. If you slowly accelerate…

> Fair warning: everything I know about orbital mechanics is from Kerbal Space Program.

Knowing what I know about that game I read this as: Warning; I actually know what I'm talking about here.

Re: Our moon has been slowly drifting away from Earth over the past 2.5B yrs

#54

Post by unnouinceput »

kubafu wrote: post #33
divbzero wrote: post #14

A curious effect of this is that total solar eclipses past and future look different from total solar eclipses today. We live in a time when both the Sun and the Moon are roughly the same size (~32 arcminutes) when viewed from Earth. This coincidence results in the image we associate with total solar eclipses where the Sun’s corona is visible as a ring around the Moon.

And another factor will be the Sun growing in size due to hydrogen exhaustion: https://en.wikipedia.org/wiki/Sun#After_core_hydrogen_exhaus... But at the time also the Earth's average distance from the Sun will grow, wouldn't it?

No, it won't. Earth will either be a scorched planet or will be engulfed by the Sun. And it won't take those 5 billion years either for life to vanish from Earth. We're currently near the inner edge of Goldilocks zone (Mars is just a bit outside of the outer edge) and we have only like 500 million years. Either start colonizing other planets or we die, there nothing in between (assuming we don't destroy ourselves meanwhile).

Re: Our moon has been slowly drifting away from Earth over the past 2.5B yrs

#55

Post by d0mine »

consp wrote: post #30
charcircuit wrote: post #17

Earlier quoted context omitted.

In even 1000 years that would only be an offset 38 meters. That wouldn't meaningfully change the ratio.

While not overwhelming an orbit change of 38000km per 1b years sounds more than enough to change that image.

38000km is just 10% of the current Moon-Earth distance and on the time scale of billions years, there are other things to worry: "the Sun will likely engulf Earth in about 7.59 billion years." https://en.wikipedia.org/wiki/Future_of_Earth#:~:text=Earth%....

Re: Our moon has been slowly drifting away from Earth over the past 2.5B yrs

#56

Post by ben_w »

unnouinceput wrote: post #54
kubafu wrote: post #33

Earlier quoted context omitted.

And another factor will be the Sun growing in size due to hydrogen exhaustion: https://en.wikipedia.org/wiki/Sun#After_core_hydrogen_exhaus... But at the time also the Earth's average distance from the Sun will grow, wouldn't it?

No, it won't. Earth will either be a scorched planet or will be engulfed by the Sun. And it won't take those 5 billion years either for life to vanish from Earth. We're currently near the inner edge of Goldilocks zone (Mars is just a bit outside of the outer edge) and we have only like 500 million years. Either start colonizing other planets or we die, there nothing in between (assuming we don't destroy ourselves mea…

Third option, we can take advantage of repeated gravitational slingshots to transfer orbital kinetic energy from Jupiter to Earth via an asteroid going repeatedly between both planets, gradually increasing Earth's orbit.

(I'm not an astrophysicist, I just read about this idea a few years back and it stuck in my mind).

Re: Our moon has been slowly drifting away from Earth over the past 2.5B yrs

#57

Post by cwillu »

robertlagrant wrote: post #53
aussieshibe wrote: post #21

Earlier quoted context omitted.

Fair warning: everything I know about orbital mechanics is from Kerbal Space Program. The moon cannot orbit at a higher speed while keeping the same semi-major axis (average distance to the orbital centre of mass). If you suddenly doubled the orbital speed of the moon right now, the apoapsis (the highest point in its orbit relative to the orbital centre of mass) would increase significantly. If you slowly accelerate…

> Fair warning: everything I know about orbital mechanics is from Kerbal Space Program. Knowing what I know about that game I read this as: Warning; I actually know what I'm talking about here.

It depends; there's actually a mod that adds realistic n-body gravity, and it's remarkable how much it affects.

Re: Our moon has been slowly drifting away from Earth over the past 2.5B yrs

#58

Post by soliton4 »

-- quote -- These have shown that the moon is currently moving 3.8 cm away from the Earth every year.

If we take the moon's current rate of recession and project it back in time, we end up with a collision between the Earth and moon around 1.5 billion years ago. -- end quote --

3.8 cm * 1.500.000.000 = 5.700.000.000 cm = 57.000.000 meter = 57.000 km

distance between earth and moon = 384,399 km according to https://en.wikipedia.org/wiki/Lunar_distance_(astronomy)

what is wrong here?

Re: Our moon has been slowly drifting away from Earth over the past 2.5B yrs

#59

Post by JaimeThompson »

soliton4 wrote: post #58

-- quote -- These have shown that the moon is currently moving 3.8 cm away from the Earth every year. If we take the moon's current rate of recession and project it back in time, we end up with a collision between the Earth and moon around 1.5 billion years ago. -- end quote -- 3.8 cm * 1.500.000.000 = 5.700.000.000 cm = 57.000.000 meter = 57.000 km distance between earth and moon = 384,399 km according to https://en…

The rate at which the moon moves away from the Earth isn't constant. I can't find the details right now so I could be totally wrong.

Re: Our moon has been slowly drifting away from Earth over the past 2.5B yrs

#60

Post by soliton4 »

JaimeThompson wrote: post #59
soliton4 wrote: post #58

-- quote -- These have shown that the moon is currently moving 3.8 cm away from the Earth every year. If we take the moon's current rate of recession and project it back in time, we end up with a collision between the Earth and moon around 1.5 billion years ago. -- end quote -- 3.8 cm * 1.500.000.000 = 5.700.000.000 cm = 57.000.000 meter = 57.000 km distance between earth and moon = 384,399 km according to https://en…

The rate at which the moon moves away from the Earth isn't constant. I can't find the details right now so I could be totally wrong.

thats true, however the author explicitly stated that the collision point of earth and moon at 1.5 billion years was calculated by assuming the moons CURRENT rate of recession
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