How to find the terminal point?

I was doing my homework and was stuck on a problem for a really long time, and eventually checked the answer key to try and see if I could understand the solution. This is the first part but I still don't understand what it is saying.

For this question, we're going to use our filled in unit circle:

By definition, answers the question "What is the angle between $-\pi/2$  and $\pi/2$  with a sine of $\frac{-\sqrt{3}}{2}$?" Since the sine is the vertical coordinate of the corresponding terminal point, we see that the only such angle in the interval is $-\pi/3$ which means that $\arcsin\left(-\frac{\sqrt{3}}{2}\right)= -\frac{\pi}{3}$

Can someone explain to me how this works? Because aren't there two intervals where the angle is? Sorry if this doesn't make sense. All help is greatly appreciated.