It's fascinating to learn about nature because much of it differs from common understanding. For example, what is light? How much light do we see? Are there things we don't see?
These questions are important. Light is electromagnetic radiation that appears on a wide spectrum. There are many regions of light, from radio waves to gamma waves, but what humans see is only a tiny sliver in the middle of the spectrum. If you imagine that spectrum the length of the Brooklyn Bridge, what humans see is only two feet wide. The rest of the spectrum is "invisible" to us.
This is why "black holes", which science recently discovered, are "invisible" -- they project only X-ray light humans can't see. If you look through the world's most powerful telescope, you can't see a black hole. We found them through their effect on other celestial bodies. Using math, we confirmed their existence by noting their gravitational force on other stars. No human can "see" a black hole which is why scientists debated for decades whether they really exist.
Here on Earth there are many animals that see light that's invisible to us. Birds and insects, for instance, see UV light that enables them to find food. Snakes see infrared light which lets them see warm-blooded prey in pitch-black night.
Humans see by having light cells in our eyes that detect color (cones) and intensity (rods). While we have only three types of cones, many animals have four, enabling them to see UV light. They find this handy for locating things to eat. Dogs have only two cones so they can't see colors red and green. Cats too have fewer cones but more rods so they see greater detail in low-light, making them good hunters.
The greatest human fallacy is to believe that if we don't see something, it doesn't exist. That was disproven by the recent discovery of black holes. It's also disproven by animals who possess sensory capabilities we lack; they perceive the world differently and see things we can't. Nature is amazing whether we know it or not.
