If vectors $ \overrightarrow{A} = \cos \, \omega t \, \widehat{ i} + \sin \, \omega \, t \widehat{j}$ and $ \overrightarrow{ B} = \cos \, \frac{ \omega \, t }{ 2} \widehat{i} + \sin \, \frac{ \omega \, t }{ 2} \widehat{j}$ are functions of time, then the value of $t$ at which they are orthogonal to each other is