Snell’s window

What is Snell’s Window?

Snell’s window, also known as the circle of least confusion, is a phenomenon that occurs when an observer looks at the underwater world from above. It is a circular patch of light that appears on the surface of the water, and it is named after the Dutch mathematician Willebrord Snell. The window is a result of the way that light refracts as it passes from one medium to another, such as from air to water.

The Physics Behind Snell’s Window

When light travels from one medium to another, such as from air to water, it changes direction. This change in direction is called refraction, and it can cause objects to appear distorted or even disappear when viewed through the water’s surface. However, when the angle of incidence of the light is less than a certain critical angle, known as the Brewster angle, the light is refracted in a way that allows it to reach the observer’s eye without undergoing total internal reflection. This creates a circular patch of light on the water’s surface, which is Snell’s window.

Examples of Snell’s Window in Nature

Snell’s window can be observed in a variety of natural settings, such as when looking down into a swimming pool, watching fish swim in a river, or observing the ocean from a boat. It is also a common phenomenon in nature documentaries, where filmmakers use it to capture stunning underwater footage. The effect can be particularly striking when the light is coming from a low angle, such as during sunrise or sunset, and the water surface is calm and flat.

Snell’s Window in Underwater Photography

Snell’s window is a popular subject for underwater photographers, who use it to create dramatic images that play with the viewer’s perception of space and scale. By positioning the subject of the photograph below the window, the photographer can create a sense of depth and distance, as well as an otherworldly sense of weightlessness. Snell’s window can also be used as a natural frame or vignette that draws the viewer’s eye to the subject of the image. Overall, Snell’s window is a fascinating natural phenomenon that has captured the imagination of scientists, artists, and photographers alike.