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**Diffraction pattern??**

This isn't a homework problem, but something I noticed and would like to understand. Hopefully I have posted this in the right area:

I have a window that faces west. The other day I noticed a perfectly circular patch of light (several inches in diameter) on the wall directly opposite my window (which had curtains on it, pulled closed). At first I couldn’t figure out where the light was coming from, so I stood in front of the wall with the light pattern on my chest and walked forward to try to find the source. As I got closer to the window, the light pattern became rectangular and I realized it was coming from the vertical slit between the drapes that were covering the window. After opening the drapes, I realized the sun was low in the sky and looked like a small round ball of light. So the light on the wall was the image of the sun. As I closed the drapes again, the slit in the drapes became longer (just because of the way they fell closed). I turned around to look at the light pattern on the wall again, and there were about 10 perfect circles of light in a vertical line from floor to ceiling, all the same size, same intensity. So what was I observing? Is this diffraction through a slit? Why does the size of the slit determine how many circles I see, and why does the light pattern change from circular to rectangular the closer I get to the window (like the circles all shrink together to make a rectangle, like the slit in the drapes)?

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