 The disks of most stars are much too small in angular size to be observed with current ground @-@ based optical telescopes , and so <unk> telescopes are required to produce images of these objects . Another technique for measuring the angular size of stars is through <unk> . By precisely measuring the drop in brightness of a star as it is <unk> by the Moon ( or the rise in brightness when it reappears ) , the star 's angular diameter can be computed . 
