The WMAP objective is to measure the temperature differences in the

[azizlwl]

The WMAP objective is to measure the temperature differences in the Cosmic Microwave Background (CMB) radiation.

My question are,
1.How to distinguish all the radiations of 13 billion years ago from others of the latter ones.
2.How the distance of radiation source is measured.

Thanks.

 

[Chalnoth]

The WMAP objective is to measure the temperature differences in the Cosmic Microwave Background (CMB) radiation.

My question are,
1.How to distinguish all the radiations of 13 billion years ago from others of the latter ones.
2.How the distance of radiation source is measured.

Thanks.

By the spectrum. The CMB has a black body spectrum at 2.725K, with tiny differences in this temperature from place to place at a level of about one part in one hundred thousand in temperature.

Other things we see in the sky have very different emission rates. Most are not black bodies, and tend to have temperatures very different from the CMB. So they will emit more radiation at low frequencies and less at high frequencies, or vice versa, depending upon how the radiation is emitted.

It is for this reason that the WMAP satellite measures the sky at not one but five different frequencies, from 23GHz to 94GHz. The Planck satellite, which is expected to release its first cosmological results next year, measures the sky at nine different channels from 30GHz to 857GHz, so that it is even better at distinguishing between the CMB and other stuff out there.