A small piggy looks at us from the surface of a shell which has a hole at the top. If you try to catch the piggy your hand grasps the air.

The toy is made of two concave mirrors facing each other. In the hole of the top mirror a reflection of the piggy is created. But the pig is standing at the bottom.

The phenomenon of mirage experienced on a desert is a reflection of a distant oasis. The image is created by the light beams curved over the heated sand.

The toy is made of two concave mirrors facing each other. Both mirrors have the same focal length, and the distance between the mirrors (along the optical axis of the set) is equal to this focal length (i.e. it is half the length of the radius of the curve).

Light beams radiating from the object bounce back to the focal point of the upper mirror where they are reflected parallel to the optical axis of the set and they run towards the bottom mirror. Then they are reflected by the bottom mirror towards its focal point which is located in the aperture in the upper mirror. As a result a reversed real image of the object is created in the aperture.

The calculation where the image is created is more difficult. Since the object is located in the focal point (p = R/2), the first image, according to concave mirror equation:

1/p + 1/q = 2/R

is created within the distance of infinity q = ∞.

Due to a spherical aberration the object, whose mirage we want to obtain by means of this toy has to be relatively small and short with relation to the radius of the mirror curve.

MA mirage on the desert is created in a different way - warming up of the air near the ground, changes its refractive index (smaller near the ground, larger higher above). As a result light rays undergo bending, as they do in a fibre-optic cable, and mirages are created in the air.