Interferometric Measurements of the Green Corona Line During the Total Solar Eclipse of 1954 June 30

Abstract

A detailed description is given of a successful attempt to observe interference fringes with a Fabry–Perot interferometer from the 5303 A corona line during a total eclipse. Low-absorption coatings for the interferometer and a narrow pass-band interference filter (equivalent width of ~25 A of the continuous spectrum, peak transmission 25 per cent) have been employed. In spite of thin cloud during totality, which was estimated to have reduced the available intensity by a factor of 2, it proved possible to measure fringe half-widths for various position angles and distances from the solar limb. The measurements seem to indicate a decrease of the line widths with increasing distance from the Sun. Interpreted in terms of kinetic temperatures, |$T=2.2\times{10}^{6}\,\text{to}\,5\times{10}^{6}$| deg. K, with most values near |$2.5\times{10}^{6}$|⁠, for regions situated 1.05 to 1.3 radii from the solar centre. The paper concludes with suggestions for improvements to the equipment for a future occasion.