Solar Constant: First Direct Measurements

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Science  30 Aug 1968:
Vol. 161, Issue 3844, pp. 888-891
DOI: 10.1126/science.161.3844.888


The solar constant was directly measured from an altitude of about 82 kilometers-apparently the first such determination. The total solar intensity was 136.1 milliwatts per square centimeter, or 1.952 calories per square centimeter, per minute-about 2.5 percent less than Johnson's derived value. Energy in the ultraviolet and visible regions (for λ less than 607 nanometers) was 7.0 percent less than that obtained by integration over Johnson'Scurve; for integral flux of λ greater than 607 nanometers there was almost perfect agreement. Seven supporting series of measurements from lower altitudes agreed extremely well with these results after correction for atmospheric extinction.