Emission of helium in prominences and the chromosphere

The excitation of the levels (2¹ P, 3¹ D, 5¹ D, 6¹ D and 7¹ D) of helium in quiescent prominences and the chromosphere is considered using the observations made during the 1952, 1961 and 1970 solar eclipses (Thomas and Athay, 1961; Athay and Orrall, 1957; Rigutti and Russo, 1964; Kubota et al., 1972) as well as by means of high altitude coronographs (Jefferies and Orrall, 1962). It is shown that the lower levels of the singlet series of helium, like the lower levels of hydrogen, are excited by resonance (λ = 584 Å) and photospheric radiation. The higher levels are populated by transitions from the triplet system, so that a relative state LTE is established between the systems for n ? 6.