The Koobi Fora experiment: continuum observations of solar spicules during the 30 June 1973 eclipse.

Summary. Limb observations of chromospheric spicules in the continuum near 4700 A were obtained during the solar eclipse of 30 June 1973, in an experiment conducted close to the edge of the path of totality in northern Kenya. The experimental apparatus and observing techniques which were employed are described and some results of the data analysis are presented. The observations indicate that spicules may extend to substantially greater heights in the corona than one infers from filtergrams and spectra of the stronger spicule emission lines. The derived continuum intensity distribution within a single chromospheric emission feature is interpreted as being due to the collective effect of one or more spicules within the "blur circle" defined by the quality of the seeing during eclipse. This intensity distribution, when corrected for the probable number of spicules contributing to the observed emission at each height, leads to a straightforward determination of the spicule electron density as a function of height, since the continuum emission is almost certainly the result of Thomson scattering of photospheric radiation by free electrons. The inferred densities at heights less than 10000 km are in reasonable agreement with previous determinations. Key words: eclipse electron scattering spicules