Zenith sky brightness and airglow emissions during the equatorial solar eclipse of 30 June 1973

Experimental and calibration procedures used for photometric zenith measurements at Loiyengalani (2.75 degrees N, 36.6 degrees 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-A range during totality and morning twilight at Dar es Salaam. The twilight 3914- and 6300-A 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 A was <1 kR/A, somewhat lower than has been observed at low latitudes during the past 50 years. Comparison of the 6300-A line emission rate of 1.4 +/- 0.6 kR with the Jan. 1974 Atmosphere Explorer satellite dayglow analysis suggests the main source of O((1)D) atoms during totality is by excitation of O((3)P) atoms in the lower thermosphere. About 1 kR of 5577 A was also observed, but the 5200-A emission was too low for reliable detection. An unexpectedly high 3914-A emission rate of at least 1 kR was apparent, the high rate being supported by observation at 4278 A.