Abstract

Experimental and calibration procedures used for photometric zenith measurements at Loiyengalani (2.75°N, 36.6°E) during the total solar eclipse of 30 June 1973 are described briefly. Comparison was made between sky brightness at wavelengths in the 3914–6300-Å range during totality and morning twilight at Dar es Salaam. The twilight 3914- and 6300-Å sky background ratio is sometimes close to the expected value for a pure Rayleigh molecular scattering process, but the corresponding ratio at eclipse mid-totality is about one-third this, indicating a shift toward the red consistent with an atmosphere containing aerosols. The zenith sky brightness at 5600 Å was <1 kR/Å, somewhat lower than has been observed at low latitudes during the past 50 years. Comparison of the 6300-Å line emission rate of 1.4 ± 0.6 kR with the Jan. 1974 Atmosphere Explorer satellite dayglow analysis suggests the main source of O(1D) atoms during totality is by excitation of O(3P) atoms in the lower thermosphere. About 1 kR of 5577 Å was also observed, but the 5200-Å emission was too low for reliable detection. An unexpectedly high 3914-Å emission rate of at least 1 kR was apparent, the high rate being supported by observation at 4278 Å.

© 1981 Optical Society of America

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Zenith Skylight Intensity and Color during the Total Solar Eclipse of 20 July 1963

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