<p>Given the z redshift of 1089, and the temperature difference between then and now of about 1089, I tried scaling the ev, freq. and wavelength by 1089....</p>
<p>Is that right?</p>
<p>I get a freq. of about 240 Terahertz, 1.25 micron wavelength and almost exactly 1 ev of photon energy.....</p>
<p>Does that correspond to a blackbody
temperature of just under 3000 K?</p>

CC BY-SA 4.0
2020-08-10T12:29:29.913Z
I just went to Omni's online black body calculator and got 965 nm (or .965 micron) wavelength and THz for freq., after typing in 3000 K.  Is that close enough?
Kurt Hikes
CC BY-SA 4.0
2020-08-10T12:38:40.153Z
In the above comment, I meant 180 THz.
Kurt Hikes
CC BY-SA 4.0
2020-08-10T12:43:05.237Z
I know the Omni Wien's black body calculator's 'peak frequency' doesn't match it's 'peak wavelength' precisely.... Maybe because 'spectral radiance' peak values are different if you start with freq. than if you start with wavelength... (See Wikipedia article on the CMB if confused...)
Kurt Hikes
CC BY-SA 4.0
2020-08-10T14:01:19.333Z
Orange. See https://physics.stackexchange.com/a/133943/123208
PM 2Ring
CC BY-SA 4.0
2020-10-01T15:45:50.137Z
I thought more people would be curious about this...
Kurt Hikes
<astrophysics><redshift><temperature><cosmic-microwave-background><black-body>
What was the energy/wavelength/frequency of the CMB when first emitted/released?
Kurt Hikes
# What was the energy/wavelength/frequency of the CMB when first emitted/released?

(Asked by: username_0 on 2020-08-10)

Given the z redshift of 1089, and the temperature difference between then and now of about 1089, I tried scaling the ev, freq. and wavelength by 1089....

Is that right?

I get a freq. of about 240 Terahertz, 1.25 micron wavelength and almost exactly 1 ev of photon energy.....

Does that correspond to a blackbody
temperature of just under 3000 K?

**Tags:** astrophysics, redshift, temperature, cosmic-microwave-background, black-body
> **Comments:**
> **username_0**: I just went to Omni's online black body calculator and got 965 nm (or .965 micron) wavelength and THz for freq., after typing in 3000 K.  Is that close enough?  
> **username_0**: In the above comment, I meant 180 THz.  
> **username_0**: I know the Omni Wien's black body calculator's 'peak frequency' doesn't match it's 'peak wavelength' precisely.... Maybe because 'spectral radiance' peak values are different if you start with freq. than if you start with wavelength... (See Wikipedia article on the CMB if confused...)  
> **username_1**: Orange. See https://physics.stackexchange.com/a/133943/123208  
> **username_0**: I thought more people would be curious about this...  

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## 0 answers

