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Origin of the Radio Waves from Space

(Herkomst der radiogolven uit het wereldruim)
  • H. C. Van De Hulst
Part of the Studies in the History of Modern Science book series (SHMS, volume 10)

Summary

Radio waves, received from any celestial object — they being the far infrared portion of its spectrum — deserve attention. Observations of small objects are prevented by diffraction. The Sun may be a measurable object for future instruments.

The radiation observed from our galaxy must be due to the interstellar gas, the stars being ruled out by their small angular dimensions and the solid smoke particles⋆ being ruled out by their low temperature.

The spectral emission of a homogeneous layer of ionized hydrogen is computed. The continuous spectrum arising from free-free transitions has the intensity of black-body radiation at wavelengths largen than 6 m and has a nearly constant intensity at wavelengths smaller than 2 m, corresponding to a large and to a small optical thickness, respectively. These intensities, shown in Figure 2, agree with those computed by Henyey and Keenan⋆ and tally fairly well with the observations. No better accordance is to be expected, owing to the unknown electron density and extension of the interstellar gas and to unsatisfactory data about the directional sensitivity of the antenna.

Discrete lines of hydrogen are proved to escape observation. The 21.2-cm line, due to transitions between hyperfine structure components of the hydrogen ground level, might be observable if the lifetime of the upper level does not exceed 4 x 108 years, which, however, is improbable.

Reber’s observation of the Andromeda nebula suggests a rather high electron density. A cosmological remark concludes the article. The low background intensity due to remote nebulae contradicts the Hubble-Tolman static model.

Keywords

Radio Wave Spiral Nebula Homogeneous Layer Radio Region Small Optical Thickness 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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References

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Copyright information

© D. Reidel Publishing Company, Dordrecht, Holland 1982

Authors and Affiliations

  • H. C. Van De Hulst
    • 1
  1. 1.Zonnenburg ObservatoryUtrechtNetherlands

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