Determination of times of second and third contact from flash spectrum sequence

Abstract

The predicted times of contact of a total solar eclipse have uncertainty of a few seconds due to (i) irregular profile of the lunar limb, (ii) difference between the geometrical and gravitational centres of the Moon's disc and (iii) possible variation in the adopted value of solar diameter. An experiment was conducted to determine the times of second and third contact by recording the flash spectrum sequence for comparison with the predictions for our camp at Robertsganj. The equipment included a 16 mm movie camera loaded with 100 ASA color negative film, a 60° prism, digital clock synchronized with radio time signals and safety filters. The entire sequence of the flash spectrum shows that H-alpha 10 emission begins to appear from 8h40m30s Strong emission in Helium (5876 Å) can be seen at 8h40m30s. Numerous emission lines flash out against very faint continuum at 8h40m46s marking the beginning of totality. Second flash begins at 8h41m37s during totality. Multiple emission lines flash against very faint and narrow continuum at 8h41m40s marking end of totality. The computed times and actual duration of totality after correction for lunar 11mb profile have been found to be in agreement to within a second with observed times.