Animals whose eyes glow green when subjected to the illumination of light are considered to be nocturnal animals. Usually, when light enters their eyes, it hits photoreceptors present on the retina. These photoreceptors transmit the received information to the brain. However, at times the light fails to hit the photoreceptors. The eyes of these animals usually have a reflective layer called the Tapetum Lucidum, a special layer located behind the retina which acts the same way as a mirror (Jacobs 27). Animals use a variety of reflective materials to provide the Tapetal reflectance, which includes cholesterol, zinc, collagen, guanine, among others. The combination of these materials provides the characteristic green glow. The green-colored eyes of the animals are visible at night because their pupils are more dilated in order to see better in dimmer light. This is a common phenomenon observed in animals such as cats, dogs, raccoons, hyenas, and lions (Warrant & Johnsen 77). It improves the animals’ eyesight and is useful when they are hunting for prey or scavenging during low light conditions.
What Causes “Red- Eye” in Flash Pictures?
The red-eye effect in photographs is the appearance of red pupils. It mainly occurs when a photographic flash is used when there is low light or darkness. It appears in the human eyes or in the animals whose eyes have the Tapetum Lucidum. The red-eye effect is mainly caused by the presence of blood vessels in the choroid located behind the retina which provides nourishment to the eye. Therefore, the red color of blood is reflected back during flash photography.
Why Does a Blue Sky Have White Clouds?
Research shows that sunlight is white, which is a combination of all the colors of the rainbow. Tiny gas molecules scatter the shorter wavelength blue light of the sun in all directions. The sky color is mainly composed of violet, but the human eyes are not very sensitive to violet and hence, the color appears as blue.
Clouds are usually composed of millions of water droplets or ice crystals. The cloud droplets have an average size of about 10 microns and though that is relatively tiny, the droplets are much bigger than the wavelength of light (Zangwill 578). The different colors of light scatter when they hit a droplet. Consequently, this redirects light in different directions. According to Dr. Kaufman, looking at a cloud from a different angle enables one to see a mixture of all the scattered colors, which is known as Mie scattering.
Why do the Clouds Appear Red at Sunset?
The color of the sun tends to vary based on time. For instance, the sun appears yellow during midday. As the sun approaches the horizon, the sunlight traverses a longer distance through the atmosphere, which makes the rainbow colors encounter atmospheric particles that are smaller in size. The result is the scattering of a large amount of blue light, which has a shorter wavelength (Le Shiffer et al. 46). The red light, having a longer wavelength is least scattered. During sunset, people’s eyes tend to be concentrated with orange and red frequencies. Moreover, a high number of particles in the atmosphere due to pollutants makes the red sunset more pronounced and clear. Clouds appear red due to the red sunlight that illuminates them.
What is the “Green Flash” seen in some sunsets in Hawaii?
When light rays travel longer distances, they tend to bend downwards as they go from the upper, less dense atmosphere to the lower, more dense atmosphere. Since the refractive index is proportional to the wavelength of light, green rays are bent more than other colored rays. As expected, blue light is refracted most. But it is scattered out of the line of sight, leaving the green light. This results in a green flash right before the sun sets completely. In Hawaii, certain atmospheric conditions such as particle size create mirages, magnifying the green flash, which would otherwise be invisible to the naked eye (Gutierrez et al. 101).
Jacobs, Gerald. Comparative Color Vision. Amsterdam: Elsevier, 2013.
Le Shiffer, Katerina, John Louis Warpakowski Furlan and Richard Tobias Inman. “Methods and Apparatus for Efficient, Automated Red Eye Detection.” U.S. Patent No. 8,374,403, 2006.
Warrant, Eric J., and Sönke Johnsen. “Vision and the Light Environment.” Current Biology, vol. 23, no. 22, 2014, pp. 990-94.
Zangwill, Nick. “Clouds of Illusion in the Aesthetics of Nature.” The Philosophical Quarterly, vol. 63, no. 252, 2013, pp. 576-96.
Gutierrez, Diego, Francisco José Serón, and Adolfo Muñoz. “Chasing the Green Flash: a Global Illumination Solution for Inhomogeneous Media.” Slovakia: ACM, 2004, pp. 97-105.