Relative Abundance of Light Frequencies?

In summary: T^4, so we would receive the same radiation (~1.3 kW/m^2, but with a completely different spectrum) if the whole sky would glow with 410K. Not... likely.
  • #1
mishima
556
34
I was curious if anyone had ever seen information about how often one frequency of electromagnetic radiation appears in the universe compared to the other. What is the most common frequency or range of frequencies, etc? Is there a way to even estimate this?
 
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  • #2
microwave dominates everything as that's the cosmic background.
 
  • #3
Ah, of course. How about second most abundant?
 
  • #4
In terms of photon number, I would expect it to be ordered by frequency: More microwave photons than infrared, more infrared than visible, more visible than UV and so on.

In terms of energy, high-energetic photons have some advantage, of course. Visible light <-> infrared might be interesting. UV, X-rays and gamma rays are rare, I would not expect that the order changes here.
 
  • #5
An object (so called black body) at any temperature will emit a spectrum of em radiation. http://faculty.virginia.edu/consciousness/new_page_6.htm shows how the spectrum varies with the temperature of the emitter and there are many more you can find. There is a maximum wavelength for each spectrum.
There are a very large number of bodies, all at different temperatures (stars, gas clouds, rocks etc.) and they all will be producing different spectra with different maxima (plus they will all be constantly absorbing radiation from elsewhere). There will be an effective 'representative' /mean temperature if you look in all directions from here which is actually pretty cold (about 3K) which is the Cosmic Microwave Background Radiation which is arriving from all directions and that implies a wavelength of around 1.8mm (long infra red).
On Earth, we 'see' a mean temperature of about 300K (dominated by the nearby Sun, of course) but most places in the Universe are nowhere near a hot source so the mean temperature, seen from an 'average location' in the Universe will probably be not far above the CMBR temperature . I think this statement must be justified on the grounds that, even from Earth (well within the Galaxy) the CMBR has been measured with some confidence - so, if even from our position, we can 'see' a significant amount of 'really empty space' then that's what you would see, all around you, at most locations in the Universe.
Is there another factor that I have left out - something obvious, to do with the statistics, perhaps?
 
  • #6
sophiecentaur said:
There is a maximum wavelength for each spectrum.
Why? The Planck spectrum does not have one, and I don't see any reason to expect a maximum wavelength.
At the other side - short wavelength - there is a sharp drop at a temperature-dependent value (if the spectrum is expressed as function of wavelength), but that is not a minimal wavelength either.
 
  • #7
I suspect sophiecentaur meant to say something like "maximum-intensity wavelength" i.e. the wavelength of the peak of the blackbody distribution.
 
  • #8
jtbell said:
I suspect sophiecentaur meant to say something like "maximum-intensity wavelength" i.e. the wavelength of the peak of the blackbody distribution.

Right. I was gibbering a bit. I meant the spectral peak (broad, of course).
 
  • #9
sophiecentaur said:
On Earth, we 'see' a mean temperature of about 300K (dominated by the nearby Sun, of course)
No, during the day the sunlight we see has a temperature of ~5850K or so (from the temperature of the Sun's photosphere). The Earth's surface is roughly 300K in some regions, so the Earth glows infrared, but the power from the Sun (during the day) greatly exceeds the Earth's thermal glow.
 
  • #10
Khashishi said:
No, during the day the sunlight we see has a temperature of ~5850K or so (from the temperature of the Sun's photosphere). The Earth's surface is roughly 300K in some regions, so the Earth glows infrared, but the power from the Sun (during the day) greatly exceeds the Earth's thermal glow.

I was merely arguing that we are (obviously) in thermal equilibrium. We must be losing the same average power that we are absorbing and that means an average effective temperature of around 300K (A simple model involving the Earth being a black conducting ball with no atmosphere, of course). The vast majority of the energy we receive is from the Sun so it 'dominates' our resulting temperature. In most other locations in space, our temperature would be only a few K.
 
  • #11
Khashishi said:
No, during the day the sunlight we see has a temperature of ~5850K or so (from the temperature of the Sun's photosphere). The Earth's surface is roughly 300K in some regions, so the Earth glows infrared, but the power from the Sun (during the day) greatly exceeds the Earth's thermal glow.
We see ~6000K in a very narrow solid angle. If you average the flux over the full hemisphere, you get a value which is a bit above 300K.

(radius of sun)/(distance to sun) is ~0.005, so the sun covers 0.005^2 of the sky. Radiation scales with T^4, so we would receive the same radiation (~1.3 kW/m^2, but with a completely different spectrum) if the whole sky would glow with 410K. Not the whole surface is perpendicular to the solar radiation, this gives a lower equilibrium temperature. In addition, Earth is not a perfect black body, of course.
 

1. What is relative abundance of light frequencies?

The relative abundance of light frequencies refers to the distribution of light wavelengths within a given environment or system. It is a measure of how much of each wavelength of light is present, compared to the other wavelengths, and is typically expressed as a percentage or ratio.

2. How is relative abundance of light frequencies measured?

The relative abundance of light frequencies can be measured using a variety of methods, depending on the specific environment or system being studied. Some common techniques include spectroscopy, which uses a spectrometer to measure the intensity of different wavelengths of light, and photometry, which measures the amount of light at specific wavelengths using filters and detectors.

3. What factors can affect the relative abundance of light frequencies?

There are many factors that can influence the relative abundance of light frequencies, including the properties of the light source, the composition of the medium through which the light is traveling, and the presence of any absorbing or reflecting materials. Additionally, the angle and distance at which the light is observed can also impact its relative abundance.

4. Why is the relative abundance of light frequencies important in scientific research?

The relative abundance of light frequencies is an important parameter in many fields of scientific research, including astronomy, chemistry, and biology. It can provide valuable information about the composition and properties of a system, and can also be used to identify and study specific substances or phenomena based on their unique spectral signatures.

5. How can the relative abundance of light frequencies be used in practical applications?

The relative abundance of light frequencies has many practical applications, such as in the development of new materials and technologies, environmental monitoring, and medical diagnostics. It can also be used in industries such as agriculture and food production to optimize growth conditions and ensure product quality. Additionally, the relative abundance of light frequencies is crucial in the design and operation of devices such as solar panels and optical sensors.

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