The Solar Emission Intensity at 11

Abstract

Observations were made during spring 1958 of the central emission intensity of the Sun at a wave-length of 11.10 μ (901 cm ⁻¹ ), by direct comparison with the emission of a black body at 1300 °K. The solar intensity was reduced to approximately that of the black body by the use of rotating sector disks, and the ratio of intensities was then measured by a calibrated electrical attenuator so that the system was independent of the detector linearity. The only subsidiary measurements needed were the absolute reflectivity of one mirror and the variation of reflectivity with angle of reflection of another. The slit width of 0.031 μ or 2.5 cm ⁻¹ was small enough to enter an atmospheric “window” where the terrestrial absorption obeys Lambert's law, thereby allowing extrapolation to extra-terrestrial intensity. The weighted mean of five measurements of the central intensity was $$I_\odot (11.10)\mu$$ = 2.408 ± 0.016 × 10 ¹⁰ erg cm ⁻² ster ⁻¹ sec ⁻¹ (per cm wave-length range). This is equivalent to a central temperature $$T_\odot (11.10)\mu$$ = 5036 ± 30°K.