The Bilderberg Model of the Photosphere and Low Chromosphere

From 17 through 21 April 1967, an international study week was held in the `Bilderberg' near Arnhem, Netherlands, with the aim of obtaining an internationally acceptable model of the solar photosphere and low chromosphere. It was found that such a model, based on observed intensities and center-to-limb observations of the solar continuous spectrum, could indeed be established. This model, henceforth called the Bilderberg Continuum Atmosphere (BCA), is shown in Table I, which gives the temperature, gas and electron pressures, and other data as functions of the continuous optical depth at 5000 Å between τ5000 = 10⁻⁷ and 25. The model is characterized by a flat temperature minimum of 4600 °K between τ5000 ≈ 10⁻² to 10⁻⁴. The model is homogeneous, and in hydrostatic equilibrium. A hydrogen-helium ratio of 10 has been assumed.