Changes

==Characteristics==

==Characteristics==

One interesting feature of the CMB is that it provides a rest frame against which one can measure the motion of galaxies and other astronomical objects. Since the cosmic microwave background is made of electromagnetic waves, a moving observer will observe a [[Doppler shift]] of the cosmic microwave background, whereas a stationary observer will not. Since the frequency of the cosmic microwave background is known (160.2&nbsp;GHz <ref name="physorg">http://www.physorg.com/tags/cosmic+microwave+background/</ref>), the velocity of the observer can easily be calculated. Our very Earth sees a Doppler shift in the cosmic microwave background, a shift that must be subtracted from measurements of the CMB to obtain its true temperature distribution.

One interesting feature of the CMB is that it provides a rest frame against which one can measure the motion of galaxies and other astronomical objects. Since the cosmic microwave background is made of electromagnetic waves, a moving observer will observe a [[Doppler Effect|Doppler shift]] of the cosmic microwave background, whereas a stationary observer will not. Since the frequency of the cosmic microwave background is known (160.2&nbsp;GHz <ref name="physorg">http://www.physorg.com/tags/cosmic+microwave+background/</ref>), the velocity of the observer can easily be calculated. Our very Earth sees a Doppler shift in the cosmic microwave background, a shift that must be subtracted from measurements of the CMB to obtain its true temperature distribution.

The thermal black-body spectrum of the cosmic microwave background is 2.725 K.<ref name="physorg"/>

The thermal black-body spectrum of the cosmic microwave background is 2.725 K.<ref name="physorg"/>