<p>What would you expect to see from a doppler effect as a result of the Earth's motion relative to the frame of the cmb?</p>
<p>I'd expect to see a globe with half &quot;red&quot; and half &quot;blue&quot;.  When that sphere that is projected onto a flat surface, I'd expect to see a &quot;yin-and-yang&quot; shape (unless by chance, the direction of motion was exactly aligned to the plane of the galaxy)</p>
<p>The &quot;poles&quot; are not aligned to the poles of the Earth (nor the poles of the sun, nor even the poles of the galaxy) the axis of the poles is the direction of motion of the Earth relative to the cmb.  So the direction does change a little as a result of the orbit of the Earth, but most of the motion is due to the motion of the sun in the galaxy and the motion of the galaxy in space.</p>
<p>The oval is a map of the whole sky, with the milky way along the middle.  The red-orange-green half is the direction of travel of the Earth (relative to the cmb) and the blue half is the side of the sky opposite to the direction of travel.</p>
<p>The blobs are mostly due to local sources of microwave radiation, that need to be subtracted from the whole to find anisotropies in the cmb.</p>

CC BY-SA 4.0
2022-10-28T03:25:54.120Z
So I would expect it to have these dipoles right at the poles of the earth, but they are offset, why is that?
realanswers
CC BY-SA 4.0
2022-10-28T05:56:57.413Z
I've edited.  The motion of the Earth relative to the cmb is not in the direction of the pole.
James K
CC BY-SA 4.0
2022-10-28T06:11:00.923Z
But note that the image is a map of the sky with the galaxy along the middle and the galactic poles at the top and bottom. The poles of the Earth (ie the pole star) is at some unknown (to me) position.
James K
CC BY-SA 4.0
2023-01-21T17:05:48.193Z
I am still confused, when we say the movement of the earth relative to the CMB, how is the CMB moving? or rather how are we moving through the CMB? is it the movement of the solar system through the milky way or?
realanswers
CC BY-SA 4.0
2023-01-21T17:10:39.290Z
In includes that motion, but it also includes the motion of the milkyway relative to the matter that filled the universe at the time of recombination.
James K
CC BY-SA 4.0
2023-01-21T19:27:45.960Z
Is there a resource you can refer me to that discusses this point in detail?
realanswers
CC BY-SA 4.0
2023-01-21T23:35:07.513Z
https://www.physics.unlv.edu/~jeffery/astro/cosmol/cmb_dipole_anisotropy.html
James K
CC BY-SA 4.0
2023-01-21T23:36:49.750Z
The dipole anisotropy is the least interesting.  It isn't related to cosmological properties, but only to the doppler shift caused by the the peculiar motion of the Solar system relative to the cosmic background.
James K
CC BY-SA 4.0
2023-01-21T23:47:28.307Z
I was looking for a more indepth discussion than the one provided. And I find it quite interesting and would like to understand it better :)
realanswers
CC BY-SA 4.0
2022-10-27T18:25:29.413Z
2022-10-28T05:55:59.860Z
2022-10-28T05:55:59.860Z
James K
<p>I do not see how this dipole anisotropy is due to the motion of the earth (and thus a doppler effect). Does anyone have a visualization of how this maps onto the earth and the motion of the earth such that I can see why it is a doppler effect?
<a href="https://i.sstatic.net/tf8GJ.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/tf8GJ.png" alt="enter image description here" /></a></p>

<cosmic-microwave-background><doppler-effect>
CMB dipole anisotropy maping to earth visualization
realanswers
# CMB dipole anisotropy maping to earth visualization

(Asked by: username_0 on 2022-10-27)

I do not see how this dipole anisotropy is due to the motion of the earth (and thus a doppler effect). Does anyone have a visualization of how this maps onto the earth and the motion of the earth such that I can see why it is a doppler effect?
[![enter image description here](https://i.sstatic.net/tf8GJ.png)](https://i.sstatic.net/tf8GJ.png)

**Tags:** cosmic-microwave-background, doppler-effect


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## 1 answers

### Answer by username_1 on 2022-10-27. Score: 3

What would you expect to see from a doppler effect as a result of the Earth's motion relative to the frame of the cmb?

I'd expect to see a globe with half "red" and half "blue". When that sphere that is projected onto a flat surface, I'd expect to see a "yin-and-yang" shape (unless by chance, the direction of motion was exactly aligned to the plane of the galaxy)

The "poles" are not aligned to the poles of the Earth (nor the poles of the sun, nor even the poles of the galaxy) the axis of the poles is the direction of motion of the Earth relative to the cmb. So the direction does change a little as a result of the orbit of the Earth, but most of the motion is due to the motion of the sun in the galaxy and the motion of the galaxy in space.

The oval is a map of the whole sky, with the milky way along the middle. The red-orange-green half is the direction of travel of the Earth (relative to the cmb) and the blue half is the side of the sky opposite to the direction of travel.

The blobs are mostly due to local sources of microwave radiation, that need to be subtracted from the whole to find anisotropies in the cmb.

> **Comments:**
> **username_0**: So I would expect it to have these dipoles right at the poles of the earth, but they are offset, why is that?  
> **username_1**: I've edited.  The motion of the Earth relative to the cmb is not in the direction of the pole.  
> **username_1**: But note that the image is a map of the sky with the galaxy along the middle and the galactic poles at the top and bottom. The poles of the Earth (ie the pole star) is at some unknown (to me) position.  
> **username_0**: I am still confused, when we say the movement of the earth relative to the CMB, how is the CMB moving? or rather how are we moving through the CMB? is it the movement of the solar system through the milky way or?  
> **username_1**: In includes that motion, but it also includes the motion of the milkyway relative to the matter that filled the universe at the time of recombination.  
> **username_0**: Is there a resource you can refer me to that discusses this point in detail?  
> **username_1**: https://www.physics.unlv.edu/~jeffery/astro/cosmol/cmb_dipole_anisotropy.html  
> **username_1**: The dipole anisotropy is the least interesting.  It isn't related to cosmological properties, but only to the doppler shift caused by the the peculiar motion of the Solar system relative to the cosmic background.  
> **username_0**: I was looking for a more indepth discussion than the one provided. And I find it quite interesting and would like to understand it better :)  

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