Wien's law and black body emition

AI Thread Summary
Black bodies emit a full spectrum of electromagnetic radiation, but Earth's atmosphere absorbs certain wavelengths, affecting observed peak wavelengths and temperatures. The peak wavelength does shift due to atmospheric absorption, which can make stars appear cooler or hotter depending on the wavelengths absorbed. The Earth's atmosphere is opaque to UV light and more transparent in the infrared, with specific absorption bands. Astronomers use advanced techniques to account for atmospheric absorption when analyzing data from telescopes. Understanding these absorption effects is crucial for accurate temperature measurements of celestial bodies.
Gabokappa
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Hi i was just wondering you when black bodies emit all spectrum of electromagnetic radiation. Now are atmosphere absorbs a particular part, therefore the peak wavelength and temperature appear to be different according to the rules of wiens law. Now does Earth atmosphere absorb Shorter wavelengths so that the peak shifts to the larger wavelength there fore black body say like a su appear cooler, or does the atmosphere absorb the longer waves, there fore peak shifts to the shorter waves and seems hotter?
 
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The peak doesn't shift.

If some frequencies are absorbed, they just aren't present in the spectrum any more (or their intensities are lower), and so the spectrum is not perfect black-body any more.
 
James R said:
The peak doesn't shift.

If some frequencies are absorbed, they just aren't present in the spectrum any more (or their intensities are lower), and so the spectrum is not perfect black-body any more.

No the peak does shift i read it in various places. Its slightly different then absorption lines. The peak wavelenght in the wiens law equation shifts. And its due to this shift that stars when observed from Earth have a slightly different temperature. But it depends which wavelengths the atmosphere absorbs. Thats what I am not sure about
 
apparently it happens both ways, depends what wavelength your looking at say UV and infra red
 
Can you quote the relevant parts of your references, or link to them, or at least say what they are?
 
A belated welcome to Physics Forums, Gabokappa!

The Earth's atmosphere is opaque to UV (we could make a more precise statement, e.g. plot the absorption as a function of wavelength), and more or less transparent into the IR, except for various bands due to absorption by water, etc (again, we could make this a more precise statement).

It is relatively straight-forward to work out what the observed spectrum of a blackbody - beyond the Earth's atmosphere - would be like, i.e. taking account of the absorption of the atmosphere. We could even plot this as a function of the temperature of the blackbody.

Astronomers have been aware of these factors for decades, if not centuries, and have developed quite sophisticated techniques for removing the effects of atmospheric absorption from the data they take from the instruments attached to their telescopes.

Do you have a particular aspect of this topic you are interested in, Gabokappa?
 
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