Have you ever noticed your cat intently watching nothing?
No matter how hard you look, there is nothing there. Scientists have recently discovered that there may really be something worth your cat’s attention. It’s that cats can see ultraviolet light and you can’t. He’s seeing into the invisible world.
Your cat really is seeing something—in ultraviolet light. SOURCE: Koshki 13
Most people have seen the science experiment using a prism. When you hold a triangle of glass to sunlight, it breaks the white light into a rainbow of color. It separates the light into different wavelengths of energy. The reds are the longest waves, oranges, yellows are shorter, and so it goes. At the other end of the spectrum are purples and violets, the shortest visible waves.
The waves you see are not the only wavelengths of light. Beyond the reds are infrared waves, which are thermo-radiation, heat waves. When you wear goggles to see infrared, you can trace animals in the dark by their body heat. On the other side of the spectrum are the even shorter waves: ultraviolet (UV). These waves can give you a tan or even sunburn or (with slightly different waves) a useful disinfectant light. Too much exposure to some ultraviolet waves can damage your eyes and cause cataracts.
Sunlight contains not only light we can see but also infrared and ultraviolet which is invisible. SOURCE: American Society for Photobiology
Scientists studying eyes have discovered that a number of animals use ultraviolet to see. Your cat and dog have UV vision, so do rats, mice, moles and bats. The birds and the bees see ultraviolet light, as do all insects, fish as well as some amphibians and reptiles.
Seeing in ultraviolet has some advantages. If you are nocturnal like a cat, and wandering in the dark, seeing more of the light spectrum is useful. Bees see patterns on flowers that help them find pollen. Rodents use it to follow urine trails. Reindeer seem to use UV vision to see polar bears, which, in visible light, blend in with the snow.
A flower in visible light and what a bee sees. SOURCE: Wikipedia
So next time you notice your cat staring intently at something invisible, remember—he may be gazing at rat pee. Aren’t you glad you don’t see it?
Evelyn Browning Garriss, historical climatologist, is a longtime writer for The Old Farmer's Almanac. She is also editor of The Browning World Climate Bulletin and has advised farmers, businesses, and investors worldwide on upcoming climate events and their economic and social impact for the past 21 years.