How Far Can We See and Why

How Far Can We See and Why?

The Human Eye Can See More Than You Think

Human eyes are capable of seeing light waves up to around 20,000 times brighter than what your eyes could perceive. These light waves are called Infrared (IR) or Visible Light. There are other types of wavelengths which our eyes cannot detect such as X-rays and Gamma Rays but they do not affect us in any way so it does not matter if we cannot see them.

Humans have three different types of cones in their eyes:

One type is sensitive to blue light. This cone allows us to distinguish between reds, oranges and yellows. The second type is sensitive to green light.

This allows us to differentiate between greens and blues. The third type is sensitive to ultraviolet (UV) light. This enables us to distinguish between infrared lights and visible lights such as sunlight or moonlight.

As humans we all have two types of rods in our eyes:

These allow us to see yellow and orange colors. They also enable us to see in black and white images. Humans also have one type of melanopsin, which enables them to see in color.

Melanopsins are found only in the skin cells, not the retina itself.

Our Eyes Are Not Just For Seeing!

In addition to helping us to see, our eyes are also able to produce tears. The tear film covers the surface of your eyes and keeps them from being damaged by dirt, dust and wind. Tears also keep our vision clear and enable us to distinguish between colours.

The cornea is the outer layer of our eyes. It is the part that you can see. The middle layer is called the Iris and it controls the size of the pupil.

The pupil is the black circle that can be seen in the middle of your eye. The retina is at the back of your eye. It converts the images that you see into electrical signals and sends them to the brain via the optic nerve, which connects your eyes and brain.

The brain then interprets these electrical signals into meaningful images. The lens inside our eyes is able to adjust its shape in order to focus light on the retina so we can see objects more clearly.

We are able to see things because the retina contains millions of light sensitive cells (Called rods and cones). Rods work best in dim light, but they do not distinguish colours well. Cones work best in well lit areas, but they do not work in the dark.

There are three different types of cones: red, green and blue. The brain is able to combine the information provided by these cells so we can see a kaleidoscope of beautiful colours.

For people who do not have working cones, the world looks like a black and white photo. Most colourblind people cannot distinguish between red and green colours.

Light waves travel in different wavelengths. The wavelengths we are able to see are from approximately 390 to 700 nanometers (nm). Each wavelength has a different colour.

The colours of the rainbow go from Violet (The shortest wavelength) to Red (the longest wavelength).

Violet Red

400 700

Blue Green Yellow Or an ge

The colour of an object depends on the wavelength of light it reflects and absorbs. For example, we see grass as green, because it reflects green wavelengths and absorbs all other wavelengths. If an object reflects red and blue wavelengths and absorbs all the rest, we will see that object as purple.

How is this useful?

There are many animals that are able to see colours that we cannot. For example, bees and spiders can see the ultraviolet (UV) light that is invisible to humans. UV light has a wavelength of between 100 and 400 nm. This means it has a shorter wavelength than violet light. Birds, reptiles, fish, and many other animals can also see into the ultraviolet spectrum.

Light travels in waves and each colour has a different wavelength.

Infrared (IR) light has a longer wavelength than red light. We cannot see this type of light, but some animals such as rattlesnakes can. They are able to sense the body heat of their prey in the same way we can see its shadow on the ground.

Have you ever seen objects through night vision goggles or in a dark room with a candle?

The objects give off far less visible light than normal, but they glow with an eerie green colour. This is because the goggles are picking up infrared light.

Have you ever wondered what it would be like to see in the dark or able to see invisible objects?

So have scientists and they have developed tools to help you do just that.

Some animals naturally see in the dark (Have you ever heard of a cat’s eyes at night?

). Others have adapted to such an extent that they can see better than us in the dark. Toothed whales, some birds (Like the common house martin) and many insects have a layer of tissue behind their eyes called the “tapetum lucidum”. This layer reflects light back to the light-sensitive cells in the retina, giving these animals night vision.

Detection of heat is another way that animals sense their surroundings. This process is known as thermoreception. Most mammals, including humans, are able to sense heat differences in their surroundings.

We use this process subconsciously every day when we feel the difference in temperature between a room and the hallway. There are three types of Thermal Sensor:

* Anterior Lobe Thermoreceptors – These are nerves in the front of your tongue that respond to warm and cool sensations but do not respond to the actual heat or cold of an object. This is why you do not burn yourself when you drink something that is too hot. You do not taste the heat.

* Pain Sensitive Thermoreceptors – These are nerves in the skin that detect high temperatures resulting in extreme pain.

* Temperature Receptor – These are nerves that can detect both extremes of heat and cold.

Have you ever been camping?

Well if you have, you may have noticed that when it is night time it becomes much colder. This is because the sun’s heat is not present and there is no replacement heat source.

Sensing the world around us involves more than just using our eyes, ears and the use of tools. It also involves the senses of taste, smell, touch, and even our instinct or intuition. Chemical sensors allow animals to taste and smell their surroundings.

Have you ever noticed how good food tastes when you are really hungry?

This is because our sense of taste increases when we are hungry. Food also tastes better when we eat it with the sense of smell. This is why when you have a cold your food doesn’t taste as good. You can’t smell it! Most animals rely heavily on their sense of taste to tell them whether their food is poisonous or not. We use only a small portion of our taste buds so that we are not overwhelmed with taste and don’t get sick of the same food all the time.

Most animals have a much better sense of smell than us. Some, such as dogs, rely heavily on their sense of smell for everything. They can tell whether you are nervous, scared or even happy by your scent!

The sense of touch is also important when sensing the environment. This is how most animals get information about their physical environment. This is how we tell whether an object is hot or cold, sharp or blunt, smooth or rough.

Some animals such as the American Bison have thick coats to protect them from the harsh winter.

A good sense of touch can also be used for defence. The porcupine has hundreds of small quills that point out from its skin that can easily prick anyone who tries to touch it. Many animals such as the hedgehog and the pangolin have a thick armour of scales to protect them from predators.

Many animals rely heavily on their sense of hearing. Some animals such as the Owl are known as silent killers because of their exceptional hearing allowing them to hunt at night with ease. The main use for most animals though is to tell them when danger is near so that they can either fight or take flight.

Some animals have more acute senses than others. They may be able to hear, see, smell or taste things that we cannot. For example, dogs can hear sounds that are inaudible to us, such as higher pitch noises.

Some snakes can even smell the change in your scent that occurs just before you have a heart attack!

The world is an amazingly diverse and exciting place with many different animals. Each animal has its own set of senses that allow it to sense the world around it and respond accordingly.

The human senses are the five traditional senses: touch, taste, sight, hearing and smell. The human senses allow a person to perceive their surroundings and respond to it accordingly.

The sense of touch is used to tell the difference between anything either soft or hard. This sense is usually perceived through the hands, but sometimes it can be perceived through other parts of the body, such as lips and feet.

The sense of taste allows a person to distinguish foods and drinks according to their taste. This one of the least important human senses because most humans do use this sense to avoid poisons or anything that might harm them.

The sense of sight is the most important human sense because it helps a person to see their surroundings clearly. It is so important that a person who cannot see is considered to be handicapped or even disabled.

The sense of smell allows an individual to distinguish different smells. While this is not the most important human sense, it can be used to help them avoid dangers or follow a path.

Hearing is another human sense that is used to perceive sounds in the environment. It is also one of the most important senses because people can use it to identify dangers and other things from afar.

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