Cycle related solar vacuum ultraviolet (VUV) variability Various studies has shown that the Sun was in an extremely inactive state during the prolonged minimum of the cycle 23 compared to other recent minima. Following these studies in this thesis work it was tried to have a closer look at the variability of the quiet Sun network and internetwork radiance between the last two solar minima. The aim of this dissertation is to find out whether there is a change in the radiance properties of the upper chromosphere and transition region (at some specific wavelengths of the VUV spectrum) over the last solar cycle. We carried out a statistical study ...