When I was a kid I happened to encounter a solar eclipse. I was taught that I should not look at the Sun directly when it is undergoing an eclipse, but I was extremely curious to see it.
Somebody suggested to me that if I created a pinhole in cardboard and place the cardboard in the Sun and managed to get the light passing through the pinhole on a screen inside the room then I could see the eclipse on the screen. I did that and I could see the eclipse on the screen.
My question is, why was I not seeing a circular illumination on the screen? But to my surprise, as the eclipse was progressing on the Sun, the illumination I saw on the screen was also undergoing the same eclipse! It means the illumination on the screen was the image of the Sun!
Why was it not a uniformly illuminated circular patch on the screen? Why was it undergoing an eclipse? The light was passing through all the portions of the hole, so why was an eclipse showing on the screen?
In summary, how does a pinhole create an image of the Sun? And not always a circular illumination?
Edit1: If we place a single point source of light in front of the pinhole then it creates a circular illumination on the screen, but if we put an extended object in front of the pinhole then it creates an inverted image of the object on the screen, how? An extended object can also be considered as a collection of infinite point sources of light. If one source produces a circular patch then infinite sources should also produce the same circular patch, just of greater intensity. The shape of the patch should not change. Why does the shape of the patch change to the shape of the object on the screen? Kindly help.