Correct-Answer to Question #22:
What is the Cosmic Microwave Background Radiation?

Q.  What is the Cosmic Microwave Background Radiation?
A.  CMBR is long-wavelength electromagnetic radiation which we receive from all points of the sky.

Q.  Where does CMBR lie on the electromagnetic spectrum?
A.  It's in the microwave and far-infrared spectrum, of lower energy than visible light and most infrared, but above radio.

Q.  Is it important in the big picture?
A.  Yes, CMBR makes up more than 70% of the energy in the radiation reaching us from space -- and a lot more than 90% of the photons.

Q.  Where does it originate?
A.  From the "Oort Soup" -- all sorts of planetesimals and planets in interstellar space, distant from stars.

Q.  How is it produced?
A.  It's just normal black-body radiation from matter at low temperatures, under 3 K.

Q.  Where can I find out more?

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