Index of Refraction of Outer/Interplanetary Space

In summary, the index of refraction in interplanetary and outer space is not the same as that of a perfect vacuum due to the presence of a low density plasma. This leads to observable consequences, such as dispersion delay, which can be used to gather information about distant sources. While there is some theoretical understanding of this effect, it has not been directly measured. Additionally, there may be other factors, such as the presence of water, that can further affect the index of refraction in space. Further research and measurements are needed to fully understand the differences between the ideal vacuum's index of refraction and the index of refraction in real outer space.
  • #1
Jolb
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In electricity and magnetism, we typically assume that the relative permittivity (or dielectric constant) ε of air is equal to the "permittivity of free space" ε0, and likewise we assume that air has a relative permeability μ equal to the "permeability of free space" μ0. This is equivalent to assuming that air has the same index of refraction n as vacuum.

However, in reality, air has slightly different index of refraction from vacuum; the most obvious example is that there's some wavelength dependence in n that causes rainbows. Pretty much all substances have have an n that's different from that of the vacuum.

So my question is this: what is the index of refraction of the interplanetary space in our solar system, or in outer space (interstellar, intergalactic, etc.)? Since outer space and interplanetary space is not a pure vacuum, it must have a slightly different index of refraction... has this ever been measured? Is it observably different from the vacuum value?

Does quantum field theory predict any changes to the index of refraction of space when we go from a classical vacuum to a quantized electromagnetic field, given that the background radiation is about 3K?

In a nutshell, I want to know if there are any observable or theoretically predicted differences between the ideal vacuum's index of refraction and the index of refraction of real outer space.

Please include any references.
 
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  • #2
There are definitely observable consequences to space not being a perfect vacuum. Because space is filled with a low density plasma, the index of refraction is a function of frequency. This means the speed of light in interstellar space is a function of frequency. This means that if I observe a transient source, like a pulsar, the arrival time of the pulses is different depending on the frequency. Radio astronomers use this effect to get information on the distance to radio sources and the density of the intervening interstellar medium. Try looking up "dispersion delay". Here's a good link:

http://www.cv.nrao.edu/course/astr534/Pulsars.html
 
  • #3
Jolb said:
However, in reality, air has slightly different index of refraction from vacuum; the most obvious example is that there's some wavelength dependence in n that causes rainbows.
Rainbows come from the refraction in water, not in air.
References ;)


For visible light, it should be possible to evaluate the diffractive index, too. However, as I did not hear about a measurement yet (or do not remember it), the effect might be too small to observe.
 

1. What is the index of refraction of outer/interplanetary space?

The index of refraction of outer/interplanetary space is approximately 1.0003. This value is close to 1, indicating that light travels almost at its maximum speed in a vacuum in outer space.

2. Does the index of refraction change in different parts of outer/interplanetary space?

Yes, the index of refraction can vary slightly in different parts of outer/interplanetary space. Factors such as the density of particles and gravitational fields can affect the index of refraction in certain areas.

3. How is the index of refraction of outer/interplanetary space measured?

The index of refraction is typically measured using a spectrometer, which measures the bending of light as it passes through a medium. In the case of outer/interplanetary space, this measurement is done by observing the bending of light from distant stars as it passes through different regions of space.

4. What is the significance of the index of refraction in outer/interplanetary space?

The index of refraction in outer/interplanetary space is significant because it affects the path of light and other electromagnetic radiation through space. This can impact how we observe and study objects in outer space, as well as the accuracy of measurements and calculations.

5. Can the index of refraction of outer/interplanetary space be manipulated?

No, the index of refraction in outer/interplanetary space cannot be manipulated by humans. It is a natural property of space that is influenced by factors such as the density and composition of particles in a given region. However, scientists can account for the effects of the index of refraction in their studies and calculations.

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