Abstract
The photometry of coronal colour negatives is carried out. The films were obtained at the March 7, 1970 and July 10, 1972 eclipses. A distribution of the coronal brightness in the red (635 nm), green (545 nm), and blue (455 nm) wavelength intervals up to distances of (6–7)R ⊙ is deduced (Figure 1). Colour indexes of the corona (the emission ratio red/blue - C rb and green/blue - C gb) have been obtained. We assume C rb = C gb = 1 in the inner corona (≤2R ⊙). The maximum of colour indexes of the 1970 corona are at the distances of about 4R ⊙ (C rb≤ 1.9 and C gb ≤ 1.7). A slight reddening within the limits of the errors was found in the 1972 corona.
There is a correlation between colour indexes and diffuse external reinforcements (RED) brightness. The analysis of the results leads to the conclusion that RED consists of dust grains with radii ≥1 μm. RED brightness is evaluated to be 4 × 10-10 B ⊙. There is 1 grain of dust in the elementary volume with cross section of 1 cm2 along the line of sight. The intensity of dust emission in wavelength interval 10 μm deduced by the authors is approximately 1 μW cm-2 s m−1. That is in agreement with Mankin et al. (1974) and Léna et al. (1974) observations. The whole dust mass of RED is ≤1% of the coronal gas mass contained within RED region. The dust grain number density is about 10-11 cm-3.
Determinations of the colour of the solar corona have been made by a number of scientists (Tikhov, 1940, 1957; Allen, 1946; Blackwell, 1952; Michard, 1956; Sharonov, 1958; Nay et al., 1961). The corona colour was found to be somewhat redder than the Sun's. However this question is not finally settled to date.
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Ajmanov, A.K., Nikolsky, G.M. The colour of the solar corona and dust grains in it. Sol Phys 65, 171–179 (1980). https://doi.org/10.1007/BF00151391
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DOI: https://doi.org/10.1007/BF00151391