The solar diameter determination from data of the 1991 July 11 solar eclipse photoelectric observation

It is known that the solar diameter value obtained from the solar eclipse observations depends much less on atmospherical effects than those determined from the ground-based solar diameter measurements. The solar semidiameter, totality duration and some other parameters of the 1991 July 11 solar eclipse have been determined using photoelectric observations at 4 sites near the northern edge of the path of the total eclipse. The observational data have been obtained at the spectral band covering the wide region from 0.40 to 1.0 mu m, and effective wave-length is equal to approximately 0.65 mu m. To determine the solar semidiameter, a theoretical light curve was described by integral equation and fitted with a least squares method to each observational light curve. The solar semidiameter was one of the best-fit parameters. The lunar limb corrections have been obtained from Watt's charts, the Sun's and Moon's apparent ephemerides have been computed using LE200/DE200 fundamental ephemerides. As the solar semidiameter is a nonlinear parameter of the theoretical light curves, the nonlinear programming has been used to minimize the functional in the least squares method. The average value of the solar semidiameter obtained from 4 estimations is equal to 959 ".69 +/- 0 ".12 for Sun-Earth distance 1 AU. Due to he fact that the influence of the chromosphere light on the eclipse light curve was taken into an account partially and the linear assumption on the solar limb darkening used, the result obtained is only preliminary one. However, the results obtained show that our observation data do not contain any significant errors. The result can be corrected in future.