I've been a bit worried about that, aiming the thing at the sun through a window which is incredibly awkward.The cores were about 4 meters long and were kept upright by sticking them through a piece of board with a slightly over sized elliptical hole. You need to adjust the angle constantly as the sun travels with a speed of close to 1 degree per 15 minutes while the angular size of the sun is about 0.5 degrees.
I get it about right by looking down the barrel right at the sun and aiming. And then waiting for the blue spots to disappear.
There has to be a better way!