What I've been doing is copied each stroke, selecting the end anchor point and moving it using the arrow keys:
Is there an easier way to do the following "semi-circle ray effect" in Illustrator?
Just a few simple rotate and duplicate steps. Working from the center point and rotating around it, starting with a line segment on either the left or right.
A quick and easy way... use a Transform effect (Effect → Distort & Transform → Transform...) on a single line, setting an appropriate number of copies and rotation angle*. Set the transform origin to the edge which you want to be the center of the "ray"...
*Quick tip: you can do basic math in the angle input; so if you want 10 rays over 180 degrees, you input
180/10, and it will set the correct angle for you.
If you want varying line lengths you can create a single line for each different length with a Transform effect on each, adjusting the rotation angle and number of copies as needed...