APOD: CMB Dipole: Speeding Through the... (2022 Apr 03)

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APOD: CMB Dipole: Speeding Through the... (2022 Apr 03)

Post by APOD Robot » Sun Apr 03, 2022 4:06 am

Image CMB Dipole: Speeding Through the Universe

Explanation: Our Earth is not at rest. The Earth moves around the Sun. The Sun orbits the center of the Milky Way Galaxy. The Milky Way Galaxy orbits in the Local Group of Galaxies. The Local Group falls toward the Virgo Cluster of Galaxies. But these speeds are less than the speed that all of these objects together move relative to the cosmic microwave background radiation (CMBR). In the featured all-sky map from the COBE satellite in 1993, microwave light in the Earth's direction of motion appears blueshifted and hence hotter, while microwave light on the opposite side of the sky is redshifted and colder. The map indicates that the Local Group moves at about 600 kilometers per second relative to this primordial radiation. This high speed was initially unexpected and its magnitude is still unexplained. Why are we moving so fast? What is out there?

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Re: APOD: CMB Dipole: Speeding Through the... (2022 Apr 03)

Post by Iksarfighter » Sun Apr 03, 2022 6:54 am

So it exist an abolute motion referential in the Universe.
2 observers anywhere in the universe and with no shift/CMB are not moving one to another.

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Re: APOD: CMB Dipole: Speeding Through the... (2022 Apr 03)

Post by Chris Peterson » Sun Apr 03, 2022 1:53 pm

Iksarfighter wrote: Sun Apr 03, 2022 6:54 am So it exist an abolute motion referential in the Universe.
2 observers anywhere in the universe and with no shift/CMB are not moving one to another.
No. The CMB is the edge of the observable universe, not the the entire universe. Two different observers in the Universe each have their own observable universes, and can see different degrees of relative motion this way. This provides no universal frame of reference.
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Re: APOD: CMB Dipole: Speeding Through the... (2022 Apr 03)

Post by Iksarfighter » Sun Apr 03, 2022 2:00 pm

Chris Peterson wrote: Sun Apr 03, 2022 1:53 pm
Iksarfighter wrote: Sun Apr 03, 2022 6:54 am So it exist an abolute motion referential in the Universe.
2 observers anywhere in the universe and with no shift/CMB are not moving one to another.
No. The CMB is the edge of the observable universe, not the the entire universe. Two different observers in the Universe each have their own observable universes, and can see different degrees of relative motion this way. This provides no universal frame of reference.
OK TYVM I have now one or more years of meditation about this launched ;-)
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Re: APOD: CMB Dipole: Speeding Through the... (2022 Apr 03)

Post by orin stepanek » Sun Apr 03, 2022 2:34 pm

gacluster_wfi.jpg
Galaxy cluster toward the great attractor!
600 K /sec! Wow; we're moving so fast! 8-)
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Re: APOD: CMB Dipole: Speeding Through the... (2022 Apr 03)

Post by WWW » Sun Apr 03, 2022 3:43 pm

.


Seems this image may have been first observed ages ago...

Image Image

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Re: APOD: CMB Dipole: Speeding Through the... (2022 Apr 03)

Post by Fred the Cat » Sun Apr 03, 2022 3:48 pm

Bystander had posted a link in one of today's links. The relationship of voids to overdense regions seems like a clue to relative motions. :?:

Could it be the matter between life and death? :( Or maybe just the universe as a hole. :wink:
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Re: APOD: CMB Dipole: Speeding Through the... (2022 Apr 03)

Post by rwlott » Sun Apr 03, 2022 6:15 pm

APOD Robot wrote:
But these speeds are less than the speed that all of these objects together move relative to the cosmic microwave background radiation (CMBR).
If Neufer were here he would remind us that:
Neufer wrote (APOD 15 Jun 2014):
"CaMBRidge" is such a relic term:

http://en.wikipedia.org/wiki/CMB wrote:
<<The cosmic microwave background (CMB) is the thermal radiation assumed to be left over from the "Big Bang" of cosmology. In older literature, the CMB is also variously known as cosmic microwave background radiation (CMBR) or "relic radiation.">>
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Re: APOD: CMB Dipole: Speeding Through the... (2022 Apr 03)

Post by Ann » Sun Apr 03, 2022 7:03 pm

rwlott wrote: Sun Apr 03, 2022 6:15 pm
APOD Robot wrote:
But these speeds are less than the speed that all of these objects together move relative to the cosmic microwave background radiation (CMBR).
If Neufer were here he would remind us that:
Neufer wrote (APOD 15 Jun 2014):
"CaMBRidge" is such a relic term:

http://en.wikipedia.org/wiki/CMB wrote:
<<The cosmic microwave background (CMB) is the thermal radiation assumed to be left over from the "Big Bang" of cosmology. In older literature, the CMB is also variously known as cosmic microwave background radiation (CMBR) or "relic radiation.">>
Russell Lott
Yeah, Oxford it is, as in the 17th Earl of.

Don't want to clutter up more of this board, and I particularly don't want to write anything in the library forum, where the last entry is still Neufer's. He replied to a question by Kevin Hall. Like Kevin, I couldn't have explained why the Earth's oceans bulge on the opposite side of the position of the Moon.

Art explained it. It is a simple question of centrifugal force. (Oh, that! [Slaps head.] Suddenly I get it... why galaxies throw out those tidal tails on the opposite side of the galaxies interacting with them! Exactly!)

And when I see the toothy grin of Alfred E. Neuman, Art's signature, I automatically notice that he is off line and kind of abstractedly wonder when he will be online again...

Anyway. I, too, would have loved to hear what Art would have said about the CMB dipole. What's tugging at us? The Great Attrator? A seriously very large inhomogeneity in the observable universe which may in fact imply that the Universe as a whole is not actually accelerating, just moving a lot in certain places to smooth out dips and bumps in the mass distribution of the Universe?

Whatcha think, Art?

Ann
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Re: APOD: CMB Dipole: Speeding Through the... (2022 Apr 03)

Post by Chris Peterson » Sun Apr 03, 2022 7:11 pm

Ann wrote: Sun Apr 03, 2022 7:03 pm
rwlott wrote: Sun Apr 03, 2022 6:15 pm
APOD Robot wrote:
But these speeds are less than the speed that all of these objects together move relative to the cosmic microwave background radiation (CMBR).
If Neufer were here he would remind us that:
Neufer wrote (APOD 15 Jun 2014):
"CaMBRidge" is such a relic term:

http://en.wikipedia.org/wiki/CMB wrote:
<<The cosmic microwave background (CMB) is the thermal radiation assumed to be left over from the "Big Bang" of cosmology. In older literature, the CMB is also variously known as cosmic microwave background radiation (CMBR) or "relic radiation.">>
Russell Lott
Yeah, Oxford it is, as in the 17th Earl of.

Don't want to clutter up more of this board, and I particularly don't want to write anything in the library forum, where the last entry is still Neufer's. He replied to a question by Kevin Hall. Like Kevin, I couldn't have explained why the Earth's oceans bulge on the opposite side of the position of the Moon.

Art explained it. It is a simple question of centrifugal force.
Unfortunately, however, that's an incorrect answer. Not something Art often provided.
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Re: APOD: CMB Dipole: Speeding Through the... (2022 Apr 03)

Post by johnnydeep » Sun Apr 03, 2022 8:44 pm

Chris Peterson wrote: Sun Apr 03, 2022 7:11 pm
Ann wrote: Sun Apr 03, 2022 7:03 pm
rwlott wrote: Sun Apr 03, 2022 6:15 pm

If Neufer were here he would remind us that:


Russell Lott
Yeah, Oxford it is, as in the 17th Earl of.

Don't want to clutter up more of this board, and I particularly don't want to write anything in the library forum, where the last entry is still Neufer's. He replied to a question by Kevin Hall. Like Kevin, I couldn't have explained why the Earth's oceans bulge on the opposite side of the position of the Moon.

Art explained it. It is a simple question of centrifugal force.
Unfortunately, however, that's an incorrect answer. Not something Art often provided.
You mean the answer about the tidal bulges? So does this have the correct answer?:
https://oceanservice.noaa.gov/education/tutorial_tides/tides03_gravity.html wrote:The gravitational attraction between the Earth and the moon is strongest on the side of the Earth that happens to be facing the moon, simply because it is closer. This attraction causes the water on this “near side” of Earth to be pulled toward the moon. As gravitational force acts to draw the water closer to the moon, inertia attempts to keep the water in place. But the gravitational force exceeds it and the water is pulled toward the moon, causing a “bulge” of water on the near side toward the moon (Ross, D.A., 1995).

On the opposite side of the Earth, or the “far side,” the gravitational attraction of the moon is less because it is farther away. Here, inertia exceeds the gravitational force, and the water tries to keep going in a straight line, moving away from the Earth, also forming a bulge (Ross, D.A., 1995).
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Re: APOD: CMB Dipole: Speeding Through the... (2022 Apr 03)

Post by johnnydeep » Sun Apr 03, 2022 8:49 pm

Chris Peterson wrote: Sun Apr 03, 2022 1:53 pm
Iksarfighter wrote: Sun Apr 03, 2022 6:54 am So it exist an abolute motion referential in the Universe.
2 observers anywhere in the universe and with no shift/CMB are not moving one to another.
No. The CMB is the edge of the observable universe, not the the entire universe. Two different observers in the Universe each have their own observable universes, and can see different degrees of relative motion this way. This provides no universal frame of reference.
So, if two observers in different parts of the universe each measure no Doppler shift difference in the CMB across all directions in the sky, we can deduce nothing about what Doppler shift they would measure for each other? If so, I too, have some more pondering to do...
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Re: APOD: CMB Dipole: Speeding Through the... (2022 Apr 03)

Post by Chris Peterson » Sun Apr 03, 2022 9:13 pm

johnnydeep wrote: Sun Apr 03, 2022 8:49 pm
Chris Peterson wrote: Sun Apr 03, 2022 1:53 pm
Iksarfighter wrote: Sun Apr 03, 2022 6:54 am So it exist an abolute motion referential in the Universe.
2 observers anywhere in the universe and with no shift/CMB are not moving one to another.
No. The CMB is the edge of the observable universe, not the the entire universe. Two different observers in the Universe each have their own observable universes, and can see different degrees of relative motion this way. This provides no universal frame of reference.
So, if two observers in different parts of the universe each measure no Doppler shift difference in the CMB across all directions in the sky, we can deduce nothing about what Doppler shift they would measure for each other? If so, I too, have some more pondering to do...
Well, those two observers are seeing different CMBs, so that complicates things. And you need to be clear about what the two observers know about each other already.
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Re: APOD: CMB Dipole: Speeding Through the... (2022 Apr 03)

Post by Chris Peterson » Sun Apr 03, 2022 9:16 pm

johnnydeep wrote: Sun Apr 03, 2022 8:44 pm
Chris Peterson wrote: Sun Apr 03, 2022 7:11 pm
Ann wrote: Sun Apr 03, 2022 7:03 pm

Yeah, Oxford it is, as in the 17th Earl of.

Don't want to clutter up more of this board, and I particularly don't want to write anything in the library forum, where the last entry is still Neufer's. He replied to a question by Kevin Hall. Like Kevin, I couldn't have explained why the Earth's oceans bulge on the opposite side of the position of the Moon.

Art explained it. It is a simple question of centrifugal force.
Unfortunately, however, that's an incorrect answer. Not something Art often provided.
You mean the answer about the tidal bulges? So does this have the correct answer?:
https://oceanservice.noaa.gov/education/tutorial_tides/tides03_gravity.html wrote:The gravitational attraction between the Earth and the moon is strongest on the side of the Earth that happens to be facing the moon, simply because it is closer. This attraction causes the water on this “near side” of Earth to be pulled toward the moon. As gravitational force acts to draw the water closer to the moon, inertia attempts to keep the water in place. But the gravitational force exceeds it and the water is pulled toward the moon, causing a “bulge” of water on the near side toward the moon (Ross, D.A., 1995).

On the opposite side of the Earth, or the “far side,” the gravitational attraction of the moon is less because it is farther away. Here, inertia exceeds the gravitational force, and the water tries to keep going in a straight line, moving away from the Earth, also forming a bulge (Ross, D.A., 1995).
That's closer. It's actually pretty simple. The gravitational force on the Earth is stronger on the side closer to the Moon than on the other. Add the two force vectors, and you have a net force that pulls the ocean (and the solid Earth, as well) into an oblong shape. Nothing to do with centrifugal force. It would happen even if the Earth and Moon were stationary (assuming a mechanism to keep them from falling into each other).
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Re: APOD: CMB Dipole: Speeding Through the... (2022 Apr 03)

Post by ta152h0 » Sun Apr 03, 2022 10:08 pm

Big Bang versus the Big Sucker. Pass the ice cold one
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Re: APOD: CMB Dipole: Speeding Through the... (2022 Apr 03)

Post by Iksarfighter » Mon Apr 04, 2022 3:54 am

Chris Peterson wrote: Sun Apr 03, 2022 9:16 pm
johnnydeep wrote: Sun Apr 03, 2022 8:44 pm
Chris Peterson wrote: Sun Apr 03, 2022 7:11 pm

Unfortunately, however, that's an incorrect answer. Not something Art often provided.
You mean the answer about the tidal bulges? So does this have the correct answer?:
https://oceanservice.noaa.gov/education/tutorial_tides/tides03_gravity.html wrote:The gravitational attraction between the Earth and the moon is strongest on the side of the Earth that happens to be facing the moon, simply because it is closer. This attraction causes the water on this “near side” of Earth to be pulled toward the moon. As gravitational force acts to draw the water closer to the moon, inertia attempts to keep the water in place. But the gravitational force exceeds it and the water is pulled toward the moon, causing a “bulge” of water on the near side toward the moon (Ross, D.A., 1995).

On the opposite side of the Earth, or the “far side,” the gravitational attraction of the moon is less because it is farther away. Here, inertia exceeds the gravitational force, and the water tries to keep going in a straight line, moving away from the Earth, also forming a bulge (Ross, D.A., 1995).
That's closer. It's actually pretty simple. The gravitational force on the Earth is stronger on the side closer to the Moon than on the other. Add the two force vectors, and you have a net force that pulls the ocean (and the solid Earth, as well) into an oblong shape. Nothing to do with centrifugal force. It would happen even if the Earth and Moon were stationary (assuming a mechanism to keep them from falling into each other).
Tidal forces are proportional to 1/ cube of distance, that explains why the Moon despite of her lower mass makes even more tidal force than the Sun.

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Re: APOD: CMB Dipole: Speeding Through the... (2022 Apr 03)

Post by johnnydeep » Mon Apr 04, 2022 1:30 pm

Chris Peterson wrote: Sun Apr 03, 2022 9:16 pm
johnnydeep wrote: Sun Apr 03, 2022 8:44 pm
Chris Peterson wrote: Sun Apr 03, 2022 7:11 pm

Unfortunately, however, that's an incorrect answer. Not something Art often provided.
You mean the answer about the tidal bulges? So does this have the correct answer?:
https://oceanservice.noaa.gov/education/tutorial_tides/tides03_gravity.html wrote:The gravitational attraction between the Earth and the moon is strongest on the side of the Earth that happens to be facing the moon, simply because it is closer. This attraction causes the water on this “near side” of Earth to be pulled toward the moon. As gravitational force acts to draw the water closer to the moon, inertia attempts to keep the water in place. But the gravitational force exceeds it and the water is pulled toward the moon, causing a “bulge” of water on the near side toward the moon (Ross, D.A., 1995).

On the opposite side of the Earth, or the “far side,” the gravitational attraction of the moon is less because it is farther away. Here, inertia exceeds the gravitational force, and the water tries to keep going in a straight line, moving away from the Earth, also forming a bulge (Ross, D.A., 1995).
That's closer. It's actually pretty simple. The gravitational force on the Earth is stronger on the side closer to the Moon than on the other. Add the two force vectors, and you have a net force that pulls the ocean (and the solid Earth, as well) into an oblong shape. Nothing to do with centrifugal force. It would happen even if the Earth and Moon were stationary (assuming a mechanism to keep them from falling into each other).
The same even if the moon and earth were not rotating or orbiting each other? That can't be right. If, for the sake of argument, there was a zero mass infinitely strong pole holding the earth and moon in position relative to each other, wouldn't all the oceans of the earth eventually migrate to the side closest to the moon?
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Re: APOD: CMB Dipole: Speeding Through the... (2022 Apr 03)

Post by johnnydeep » Mon Apr 04, 2022 1:37 pm

Chris Peterson wrote: Sun Apr 03, 2022 9:13 pm
johnnydeep wrote: Sun Apr 03, 2022 8:49 pm
Chris Peterson wrote: Sun Apr 03, 2022 1:53 pm

No. The CMB is the edge of the observable universe, not the the entire universe. Two different observers in the Universe each have their own observable universes, and can see different degrees of relative motion this way. This provides no universal frame of reference.
So, if two observers in different parts of the universe each measure no Doppler shift difference in the CMB across all directions in the sky, we can deduce nothing about what Doppler shift they would measure for each other? If so, I too, have some more pondering to do...
Well, those two observers are seeing different CMBs, so that complicates things. And you need to be clear about what the two observers know about each other already.
What do you mean by different CMBs? Let's use my hypothetical "pole" idea from my post above about the earth/moon/tides. Suppose an infinitely strong zero mass pole was holding the Milky Way and Andromeda (say) in fixed position relative to each other. Wouldn't an observer in each galaxy (discounting galaxy rotation, etc) see the CMB Doppler shifted the same amount in all directions? And if so, if one measured a zero shift, wouldn't the other also?
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Re: APOD: CMB Dipole: Speeding Through the... (2022 Apr 03)

Post by Chris Peterson » Mon Apr 04, 2022 1:44 pm

johnnydeep wrote: Mon Apr 04, 2022 1:37 pm
Chris Peterson wrote: Sun Apr 03, 2022 9:13 pm
johnnydeep wrote: Sun Apr 03, 2022 8:49 pm

So, if two observers in different parts of the universe each measure no Doppler shift difference in the CMB across all directions in the sky, we can deduce nothing about what Doppler shift they would measure for each other? If so, I too, have some more pondering to do...
Well, those two observers are seeing different CMBs, so that complicates things. And you need to be clear about what the two observers know about each other already.
What do you mean by different CMBs? Let's use my hypothetical "pole" idea from my post above about the earth/moon/tides. Suppose an infinitely strong zero mass pole was holding the Milky Way and Andromeda (say) in fixed position relative to each other. Wouldn't an observer in each galaxy (discounting galaxy rotation, etc) see the CMB Doppler shifted the same amount in all directions? And if so, if one measured a zero shift, wouldn't the other also?
Again, an observer in our galaxy sees a different CMB than an observer in the Andromeda Galaxy, because we each have our own unique observable universes. Of course, as close as we are, they only differ very slightly, so they will appear very similar. But each of us still can see parts of the Universe forever hidden from the other.
Chris

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Re: APOD: CMB Dipole: Speeding Through the... (2022 Apr 03)

Post by Chris Peterson » Mon Apr 04, 2022 1:46 pm

johnnydeep wrote: Mon Apr 04, 2022 1:30 pm
Chris Peterson wrote: Sun Apr 03, 2022 9:16 pm
johnnydeep wrote: Sun Apr 03, 2022 8:44 pm

You mean the answer about the tidal bulges? So does this have the correct answer?:

That's closer. It's actually pretty simple. The gravitational force on the Earth is stronger on the side closer to the Moon than on the other. Add the two force vectors, and you have a net force that pulls the ocean (and the solid Earth, as well) into an oblong shape. Nothing to do with centrifugal force. It would happen even if the Earth and Moon were stationary (assuming a mechanism to keep them from falling into each other).
The same even if the moon and earth were not rotating or orbiting each other? That can't be right. If, for the sake of argument, there was a zero mass infinitely strong pole holding the earth and moon in position relative to each other, wouldn't all the oceans of the earth eventually migrate to the side closest to the moon?
You're ignoring the effect of Earth's own gravity on the oceans. Simplify the system. Replace the Earth with a big blob of Jello, held at a fixed distance from the Moon with a giant stick. What shape will that blob assume?
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Re: APOD: CMB Dipole: Speeding Through the... (2022 Apr 03)

Post by Ann » Mon Apr 04, 2022 2:29 pm

johnnydeep wrote: Mon Apr 04, 2022 1:30 pm
Chris Peterson wrote: Sun Apr 03, 2022 9:16 pm
johnnydeep wrote: Sun Apr 03, 2022 8:44 pm

You mean the answer about the tidal bulges? So does this have the correct answer?:

That's closer. It's actually pretty simple. The gravitational force on the Earth is stronger on the side closer to the Moon than on the other. Add the two force vectors, and you have a net force that pulls the ocean (and the solid Earth, as well) into an oblong shape. Nothing to do with centrifugal force. It would happen even if the Earth and Moon were stationary (assuming a mechanism to keep them from falling into each other).
The same even if the moon and earth were not rotating or orbiting each other? That can't be right. If, for the sake of argument, there was a zero mass infinitely strong pole holding the earth and moon in position relative to each other, wouldn't all the oceans of the earth eventually migrate to the side closest to the moon?
That's what it seems like to me.

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Re: APOD: CMB Dipole: Speeding Through the... (2022 Apr 03)

Post by Chris Peterson » Mon Apr 04, 2022 2:40 pm

Ann wrote: Mon Apr 04, 2022 2:29 pm
johnnydeep wrote: Mon Apr 04, 2022 1:30 pm
Chris Peterson wrote: Sun Apr 03, 2022 9:16 pm
That's closer. It's actually pretty simple. The gravitational force on the Earth is stronger on the side closer to the Moon than on the other. Add the two force vectors, and you have a net force that pulls the ocean (and the solid Earth, as well) into an oblong shape. Nothing to do with centrifugal force. It would happen even if the Earth and Moon were stationary (assuming a mechanism to keep them from falling into each other).
The same even if the moon and earth were not rotating or orbiting each other? That can't be right. If, for the sake of argument, there was a zero mass infinitely strong pole holding the earth and moon in position relative to each other, wouldn't all the oceans of the earth eventually migrate to the side closest to the moon?
That's what it seems like to me.
You're ignoring the gravity of the Earth itself on the oceans, which is greater by many orders of magnitude than the forces exerted by the Moon's gravity. If all the water were on the Moon side of the Earth, it would be piled up very high with respect to the center of the Earth. It would run "downhill" back towards the other side until the surface was once again nearly equidistant from the Earth's center. The Moon is able to distort the shape of our ocean surface away from a perfect sphere by just a few meters.
Chris

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Re: APOD: CMB Dipole: Speeding Through the... (2022 Apr 03)

Post by Ann » Mon Apr 04, 2022 3:11 pm

Chris Peterson wrote: Mon Apr 04, 2022 2:40 pm
Ann wrote: Mon Apr 04, 2022 2:29 pm
johnnydeep wrote: Mon Apr 04, 2022 1:30 pm

The same even if the moon and earth were not rotating or orbiting each other? That can't be right. If, for the sake of argument, there was a zero mass infinitely strong pole holding the earth and moon in position relative to each other, wouldn't all the oceans of the earth eventually migrate to the side closest to the moon?
That's what it seems like to me.
You're ignoring the gravity of the Earth itself on the oceans, which is greater by many orders of magnitude than the forces exerted by the Moon's gravity. If all the water were on the Moon side of the Earth, it would be piled up very high with respect to the center of the Earth. It would run "downhill" back towards the other side until the surface was once again nearly equidistant from the Earth's center. The Moon is able to distort the shape of our ocean surface away from a perfect sphere by just a few meters.
I still don't get it, sorry.

Tides on the Earth.png

I'm perfectly fine with the idea that the gravity of the Moon makes waters rise on the side of the Earth that is closest to the Moon. (And the fact that waters rise by only a few meters is not a concern to me.)

What I don't get - no, I don't - is how waters can rise on the side of the Earth that is opposite the Moon?

Why, oh why?

Ann
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Re: APOD: CMB Dipole: Speeding Through the... (2022 Apr 03)

Post by Chris Peterson » Mon Apr 04, 2022 3:15 pm

Ann wrote: Mon Apr 04, 2022 3:11 pm
Chris Peterson wrote: Mon Apr 04, 2022 2:40 pm
Ann wrote: Mon Apr 04, 2022 2:29 pm

That's what it seems like to me.
You're ignoring the gravity of the Earth itself on the oceans, which is greater by many orders of magnitude than the forces exerted by the Moon's gravity. If all the water were on the Moon side of the Earth, it would be piled up very high with respect to the center of the Earth. It would run "downhill" back towards the other side until the surface was once again nearly equidistant from the Earth's center. The Moon is able to distort the shape of our ocean surface away from a perfect sphere by just a few meters.
I still don't get it, sorry.


Tides on the Earth.png

I'm perfectly fine with the idea that the gravity of the Moon makes waters rise on the side of the Earth that is closest to the Moon. (And the fact that waters rise by only a few meters is not a concern to me.)

What I don't get - no, I don't - is how waters can rise on the side of the Earth that is opposite the Moon?

Why, oh why?

Ann
Because the water on the opposite side isn't rising. All of the water is being pulled toward the Moon. It's just being pulled more on the Moon side. Which is why the end result is a slightly elongated sphere.
Chris

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Ann
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Re: APOD: CMB Dipole: Speeding Through the... (2022 Apr 03)

Post by Ann » Mon Apr 04, 2022 3:29 pm

Chris Peterson wrote: Mon Apr 04, 2022 3:15 pm
Ann wrote: Mon Apr 04, 2022 3:11 pm
Chris Peterson wrote: Mon Apr 04, 2022 2:40 pm

You're ignoring the gravity of the Earth itself on the oceans, which is greater by many orders of magnitude than the forces exerted by the Moon's gravity. If all the water were on the Moon side of the Earth, it would be piled up very high with respect to the center of the Earth. It would run "downhill" back towards the other side until the surface was once again nearly equidistant from the Earth's center. The Moon is able to distort the shape of our ocean surface away from a perfect sphere by just a few meters.
I still don't get it, sorry.


Tides on the Earth.png

I'm perfectly fine with the idea that the gravity of the Moon makes waters rise on the side of the Earth that is closest to the Moon. (And the fact that waters rise by only a few meters is not a concern to me.)

What I don't get - no, I don't - is how waters can rise on the side of the Earth that is opposite the Moon?

Why, oh why?

Ann
Because the water on the opposite side isn't rising. All of the water is being pulled toward the Moon. It's just being pulled more on the Moon side. Which is why the end result is a slightly elongated sphere.

So why is the tide high in the picture at left? Maybe because the Moon is pulling the Earth's waters to the other side of the Earth?

And why is the tide low in the picture at right? Hmm... maybe because the Moon is pulling the Earth's waters to the other side of the Earth?

No, wait. The tide is low when the Moon is circa 90 degrees away from that spot on the Earth. That makes sense... or no?

Ann
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