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Emeritus
Sci Advisor
PF Gold
P: 2,977
 Quote by Mk What range of A) electromagnetic frequencies and/or B) electromagnetic frequencies we can see are MOST commonly found in the universe? How's that?
The CMB is the dominant form (by energy density) of radiation in the universe. It's at millimeter wavelengths. The dominant form of optical light, as can be seen in the link I gave, is in an emission line at around 650 nm, which is red light. This is the Balmer alpha line of hydrogen, commonly seen in regions with heavy star formation activity.