Editing Cosmic microwave background (section)

===CMBR dipole anisotropy (''ℓ'' = 1)===
CMB dipole represents the largest anisotropy, which is in the first spherical harmonic ({{nowrap|1=''ℓ'' = 1}}), a cosine function. The amplitude of CMB dipole is around {{val|3.3621|0.0010|u=mK}}.<ref name="cmbreview"/> The CMB dipole moment is interpreted as the peculiar motion of the Earth relative to the CMB. Its amplitude depends on the time due to the Earth's orbit about the barycenter of the solar system. This enables us to add a time-dependent term to the dipole expression. The modulation of this term is 1 year,<ref name="cmbreview"/><ref name="cobe">{{Cite web|title=COBE Differential Microwave Radiometers: Calibration Techniques.| url=http://articles.adsabs.harvard.edu/pdf/1992ApJ...391..466B| last= Bennett| first=C.}}</ref> which fits the observation done by COBE FIRAS.<ref name="cobe"/><ref>{{Cite journal|title=Dipole Modulation of Cosmic Microwave Background Temperature and Polarization.| last=Shosh| first=S.| journal=Journal of Cosmology and Astroparticle Physics| year=2016| volume =2016 |issue=1|page=046| doi=10.1088/1475-7516/2016/01/046 | arxiv=1507.04078 | bibcode=2016JCAP...01..046G | s2cid=118553819}}</ref> The dipole moment does not encode any primordial information.

From the CMB data, it is seen that the Sun appears to be moving at {{val|369.82|0.11|u=km/s}} relative to the reference frame of the CMB (also called the CMB rest frame, or the frame of reference in which there is no motion through the CMB). The [[Local Group]] — the galaxy group that includes our own Milky Way galaxy — appears to be moving at {{val|620|15|u=km/s}} in the direction of [[galactic longitude]] {{nowrap|1=''ℓ'' = {{val|271.9|2|u=°}}}}, {{nowrap|1=''b'' = {{val|30|3|u=°}}}}.<ref name="cmbreview"/> The dipole is now used to calibrate mapping studies.