Finding the angle between a point on a circle and the circle's center

I want to be able to tap somewhere on a circle and calculate the angle of that tap in relation to the circle's center (using a sphere collider). Is there some convenient code that would help with this?
I looked at this code but am not sure if it will help much...

Code (csharp):

1. var target : Transform;
2. function Update () {
3.     var targetDir = target.position - transform.position;
4.     var forward = transform.forward;
5.     var angle = Vector3.Angle(targetDir, forward);
6.     if (angle < 5.0)
7.         print("close");
8. }

 

It looks like this might be doing the trick:

Code (csharp):

1. var angle = 0.0;
2. angle = Mathf.Atan2(hit.point.y-object.transform.position.y, hit.point.x-object.transform.position.x)*180 / Mathf.PI;