People watch as something lights up the sky.
The people are at a fireworks show.
We can't tell if the light is from fireworks, it could be an aurora.
exists e1 x1 x2 x3 x4.(n_sky(x3) & as(e1,x4) & n_thing(x4) & Theme(e1,x2) & Actor(e1,x1) & v_watch(e1) & up(x2,x3) & n_light(x2) & n_people(x1))
exists p1 x1.(n_people(x1) & exists x2 x3.(at(x1,x2) & n_show(x2) & of(x2,x3) & n_firework(x3)))