# The size of the sun using pinhole imagery

taylorb
Does intensity of the sun affect this? I keep trying to do it, and when you have a square shape you should still see an image of the sun.. right? Well it is not working! I live in a place with VERY intense sun and no clouds... could this be the problem?

Any help!? Thanks so much...

Homework Helper
What, exactly, are you seeing? How big is the hole? How far apart are the hole and your imaging plane?

taylorb
OK... what I did was cut a square in the center of a piece of stiff construction paper. Then I covered the square with a piece of tin foil. Then I punctured the middle of the piece of tin foil with a sewing needle (very small). When I went outside I started out with the pinhole about a foot away from the piece of white paper on the ground that I was trying to project the image onto. I got a tiny dot... slightly bigger than the pinhole itself... very difficult to measure. So I moved the pinhole further away and closer to try and make the image bigger with very little change. So I have put it very close and about four and a half feet away. We are also meant to try it with a small square and it is still meant to show an image of the sun, but when I make a small square that is exactly what is projected on the piece of white paper!

Thanks!

Homework Helper
Taylor,

As a rough guide, basic geometry gives the spot size as

$$y = D_H + L \theta$$

where $D_H$ is the diameter of the hole, $L$ is the distance between the hole and the image plane and $\theta$ is the angular diameter of the Sun (in radians). In order to get a "good" image of the Sun, you will need to arrange for $L \theta$ to be larger than $D_H$.

Good luck!

shyboy
experimentally speaking, you may put some smoked glass otside the pinhole to check if light intensity affects the spot size. that is one of the way to do physics.