# 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...

#### Tide

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!

#### Tide

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.

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