Abstract
BAUMBACH1 derived in 1937 the electron densities in the solar corona from a compilation of many measurements of its surface brightness. His values for Ne have proved useful in many investigations of the physical state of the corona and the radio waves emitted by it. However, for two reasons, they are not entirely accurate. First, it has now become clear2 that only part of the surface brightness arises from electron scattering (K-component). In the outer corona the other part (F-component) is stronger. It has circular symmetry and may be ascribed to diffraction by interplanetary dust. Secondly, the brightness and shape of the corona change with the 11-year cycle of solar activity. These changes, which are partially masked by the superposition of the constant F-component, have been neglected in Baumbach‘s work.
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References
Baumbach, S., Astr. Nachr., 263, 121 (1937).
Cf. van de Hulst, H. C., Astrophys. J., 105, 471 (1947).
Nikonov, V. B., Bull. Abastumani Obs., 7, 33 (1943).
Appleton, E. V., and Hey, J. S., Phil. Mag., 37, 73 (1946).
Martyn, D. F., Proc. Roy. Soc., A, 193, 44 (1948).
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VAN DE HULST, H. Brightness Variations of the Solar Corona. Nature 163, 24 (1949). https://doi.org/10.1038/163024a0
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DOI: https://doi.org/10.1038/163024a0
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