The Blue Sun of 1950 September

1951/10/01 by R. W. Wilson · 1 voice · 1 citation
Environmental Science · #Atmospheric aerosols and clouds #Wind and Air Flow Studies

paper · doi:10.1093/mnras/111.5.478

openalex publication_date 1951/10/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/29

Abstract

This paper deals with the “blue” Sun observed at Edinburgh on 1950 September 26. Spectrophotometric observations of the “ blue ” and normal Suns give an extinction curve of the layer causing the phenomenon. This covers the wave-length range 3800–6300 A. and shows blueing on the long wave-length side, and reddening on the short wave-length side, of a minimum situated at λ 4350. This affords an experimental verification of an outstanding feature of scattering theory. It is concluded that the scattering particles producing the minimum are dielectric, and uniform in size and constitution. A relation between the size and refractive index of the dielectric particles is deduced. In addition to the selective effect, there is a heavy non-selective extinction which may arise from another system of absorbing particles in the layer. Other workers have established the source of the layer as the extensive forest fires burning in Alberta on 1950 September 23.

Cited by

• On the effects of size factor on albedo versus wavelength for light scattered by small particles under Mie and Rayleigh regimes

Discussions

• Fun fact: Canadian wildfire smoke crossed the Atlantic Ocean and turned the Sun blue in September 1950. Astronomer Robert Wilson made spectrometer observations at the Royal Observatory, Edinburgh, and [bsky, 0 points, 1 comments]

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