How does a pinhole projection allow people to observe a solar eclipse indirectly?

A pinhole projection is a safe, indirect method for observing a solar eclipse because it avoids the dangers of looking directly at the Sun, which can cause permanent retinopathy and vision loss.1

To use this technique, you create a small hole in one side of a box or use an object with multiple holes, such as a colander. By positioning the device so the Sun is behind you, the light passes through the aperture and projects an image of the eclipse onto a surface, such as the opposite side of the box or the ground.1

This works on the principles of geometrical optics, where the pinhole acts as a simple aperture that allows light rays to pass through and form an inverted image of the light source on a projection surface. Because you are viewing the projected image rather than the Sun itself, your eyes are protected from the intense light that would otherwise damage your retina.21