Interferometric Measurements of Wave-lengths : II. Measurements at 6500 a and a General Discussion of the solar red Shift

Abstract

It has been suggested that the largest wave-length displacement of solar lines to the red will be observed for resonance lines. To test this prediction the wave-lengths of a number of lines, including the calcium inter-system resonance line $${4}^{1}\,\text{S}-{4}^{3}\text{P}$$, have been measured in the 6500 A region by the method of circular channels. Contrary to the theoretical prediction the resonance line has the smallest red shift which has yet been observed. This resonance line is very faint and it appears to exemplify the phenomenon (frequently referred to by Burns) of a variation in line displacement with line strength. In a discussion of the red shifts at 6500 A, together with the earlier results at 5080 A and 6020 A, it is clear that line strength is the dominating factor affecting the shifts. In order to make a quantitative examination of this effect over all wave-length regions, line strengths are expressed in equivalent “ergs”, a unit proportional to the absolute energy absorbed by the line. If ∆ (milliangstroms) is the solar red shift at wavelength λ it is shown that there is a linear relation between $$\Delta /{\lambda }^{2}$$ and the logarithm of the equivalent “ergs”, a relationship which is applicable at all wave-lengths. 158 solar red shifts measured in the Allegheny Observatory—Bureau of Standards work are analysed in exactly the same way as the 20 Oxford results. These confirm the empirical relationship over a wave-length range extended by 1000 A, and a greatly increased range of line strengths.