Discontinuity in the Brightness of the Twilight Sky at Different Wavelengths

Abstract

A search for discontinuity in the sky twilight brightness at different wavelengths and different solar depressions for altitudes 0, 5, 10, 30, 50 & 70 degrees is done. It is found that the logarithmic of difference in the brightness log (I1-I2) of two similar patches lying at solar and anti-solar verticals are not suffering of any discontinuity, when plotted versus sun's depression. Whatever, the ratio I1/I2 shows that there is discontinuity in the curves at altitudes less than or equal 30 degrees. While for altitudes 50 & 70 degrees slight patches of discontinuities have been detected. The phenomenon of discontinuities may be referred to the changes in the sky twilight brightness due to the effect of the Earth's shadow on diffusing and luminescent layers in the upper atmosphere.