Sentence:  Similarly, the rays diverging from the sun will pass by you and converge on the point directly opposite the sun, the shadow of your head. All <WSD>sunbeams</WSD>, and thus all shadows, appear to converge there....Only perspective makes all shadows appear to converge on the antisolar point. But this point is also the center of the rainbow, so as you look at the rainbow, all <WSD>sunbeams</WSD> and shadows will lie along radii of the bow as they flow straight to its center. 
Meaning of the word marked with <WSD> tags:  A visible, narrow, and intense (relative to ambient light) ray of sunlight.