# Cosmic microwave background the same as the first visible light at 379,000 yrs after the Big Bang? How do these measure the age of the universe?

Was the CMB emitted at the same time as visible light at 379,000 yrs after the BB ? Was this a one time event ? If headed away from us, how does it measure the age of the universe?

• What does "the same as" mean in your question? I ask because of course microwaves and visible light are not the same frequency, but I cannot guess what other "same"ness you are asking about. Sep 25, 2022 at 17:18
• The CMB is blackbody radiation. It was visible when it was originally released, but it's now redshifted to the microwave band because of expansion. Its original color was approximately $$\Large{\color{#ffb46b}■}$$ Sep 26, 2022 at 0:01
• "If headed away from us" What do you mean? You can't see light that's heading away from you. The CMB was released everywhere (over a relatively short time span), heading in every direction. Sep 26, 2022 at 5:18