Solar constant: first direct measurements.
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 lambda less than 607 nanometers) was 7.0 percent less than that obtained by integration over Johnson'Scurve; for integral flux of lambda 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.
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