Solar System

Definition of Solar System

The Solar System is made up of all the planets that orbit our Sun. In addition to planets, the Solar System also consists of moons, comets, asteroids, minor planets, and dust and gas.

Everything in the Solar System orbits or revolves around the Sun. The Sun contains around 98% of all the material in the Solar System. The larger an object is, the more gravity it has. Because the Sun is so large, its powerful gravity attracts all the other objects in the Solar System towards it. At the same time, these objects, which are moving very rapidly, try to fly away from the Sun, outward into the emptiness of outer space. The result of the planets trying to fly away, at the same time that the Sun is trying to pull them inward is that they become trapped half-way in between. Balanced between flying towards the Sun, and escaping into space, they spend eternity orbiting around their parent star.

Process of Forming Solar System

This is an important question, and one that is difficult for scientists to understand. After all, the creation of our Solar System took place billions of years before there were any people around to witness it. Our own evolution is tied closely to the evolution of the Solar System. Thus, without understanding from where the Solar System came from, it is difficult to comprehend how mankind came to be.

Scientists believe that the Solar System evolved from a giant cloud of dust and gas. They believe that this dust and gas began to collapse under the weight of its own gravity. As it did so, the matter contained within this could begin moving in a giant circle, much like the water in a drain moves around the center of the drain in a circle.

At the center of this spinning cloud, a small star began to form. This star grew larger and larger as it collected more and more of the dust and gas that collapsed into it.

Further away from the center of this mass where the star was forming, there were smaller clumps of dust and gas that were also collapsing. The star in the center eventually ignited forming our Sun, while the smaller clumps became the planets, minor planets, moons, comets, and asteroids.

A Great Storm

Once ignited, the Sun's powerful solar winds began to blow. These winds, which are made up of atomic particles being blown outward from the Sun, slowly pushed the remaining gas and dust out of the Solar System. With no more gas or dust, the planets, minor planets, moons, comets, and asteroids stopped growing. You may have noticed that the four inner planets are much smaller than the four outer planets. Why is that?

Because the inner planets are much closer to the Sun, they are located where the solar winds are stronger. As a result, the dust and gas from the inner Solar System was blown away much more quickly than it was from the outer Solar System. This gave the planets of the inner Solar System less time to grow.

Another important difference is that the outer planets are largely made of gas and water, while the inner planets are made up almost entirely of rock and dust. This is also a result of the solar winds. As the outer planets grew larger, their gravity had time to accumulate massive amounts of gas, water, as well as dust.

The Solar System Has Over 100 Worlds

It is true that there are only eight planets. However, the Solar System is made up of over 100 worlds that are every bit as fascinating. Some of these minor planets, and moons are actually larger than the planet Mercury!

Others, such as Io, have active volcanoes. Europa has a liquid water ocean, while Titan has lakes, rivers, and oceans of liquid Methane. You can read more about these amazing worlds by clicking here.

The Asteroid Belt, The Kuiper Belt, And The Oort Cloud

You have probably heard about the Asteroid Belt. This band of asteroids sits between the orbits of the planets Jupiter and Mars. It is made up of thousands of objects too small to be considered planets. Some of them no larger than a grain of dust, while others, like Eros can be more than 100 miles across. A few, like Ida, even have their own moons.

Further out, beyond the orbit of the minor planet Pluto, sits another belt known as the Kuiper Belt. Like the Asteroid Belt, the Kuiper Belt is also made up of thousands, possibly even millions of objects too small to be considered planets. A few of these objects, like Pluto, are large enough that their gravity has pulled them into a sphere shape.

These objects are made out of mostly frozen gas with small amounts of dust. They are often called dirty snowballs. However, you probably know them by their other name... comets.

Every once in a while one of these comets will be thrown off of its orbit in the Kuiper Belt and hurled towards the inner Solar System where it slowly melts in a fantastic show of tail and light.

Beyond the Kuiper Belt sits a vast area known as the Oort Cloud. Here within this jumbled disorganized cloud live millions of additional comets. These comets do not orbit the Sun in a ring or belt. Instead, each one buzzes around in a completely random direction, and at extremely high velocities.

Beyond The Oort Cloud

The Sun's solar winds continue pushing outward until they finally begin to mix into the interstellar medium, becoming lost with the winds from other stars. This creates a sort of bubble called the Heliosphere. Scientists define the boundaries of the Solar System as being the border of the Heliosphere, or at the place where the solar winds from the Sun mix with the winds from other stars.

The Heliosphere extends out from the Sun to a distance of about 15 billion miles, which is more than 160 times further from the Sun than is the Earth.

 

The Planet
The planet Mercury is the closest of the planets to the Sun. Because this planet lies so close to the Sun, and as a result somewhat near to Earth, it is visible to observers on Earth in the late evening or early morning sky. Because of this, Mercury has become a part of the mythology and legend of almost every culture throughout the history of the Earth. This planet is often called a morning star. This is because Mercury shines brightly in the early morning just before the sun rises. It has also been called an evening star for the same reason. Mercury is often visible for a brief period of time just after the Sun sets.

Mercury
Because of its proximity to the Sun, Mercury's evolution took a slightly different course than that of the other planets. As the Sun formed, it pushed much of the lighter gas and dust out of the inner Solar System, leaving behind only heavier elements. As a result, Mercury is made out of a large percentage of heavier elements, mainly iron. It is essentially a large metal ball of iron with a very thin silicate crust. Mercury's core makes up about 75% of the planet. Its thin mantle, or crust, is only about 300 to 400 miles thick (500 to 600 km). Next to Earth, Mercury is the second most dense planet in our Solar System.As Mercury's iron core cooled it contracted, or shrunk. This caused its rocky crust to become wrinkled. Scientists call these wrinkles Lobate Scarps. This scarps can be hundreds of miles long and even up to a mile high. Mercury's core has not cooled completely, however. Researcher recently found evidence that Mercury has a molten core.The surface of the planet Mercury is covered with craters. These craters have been created by eons of accidental encounters with asteroids and comets. All celestial bodies within the Solar System are subject to these bombardments. However, many of the planets have the ability to heal themselves through natural geological processes. The planet Mercury is too small and has too little gravity to hold onto an atmosphere. Any gases released from the planet quickly escape into space. Also, Mercury is so close to the Sun that any atmosphere is quickly blown away by the Sun's solar winds. That means that there is almost no air on Mercury.Mercury is just a little bit larger than Earth's moon. The surface of Mercury that faces the Sun can reach about 800 degrees Fahrenheit. On the other hand, the temperature on the nighttime side can plummet to almost -300 degrees Fahrenheit. This is because Mercury has little to no atmosphere to help regulate temperature.Because of its close location to the Sun, the planet Mercury has become tidally locked to the Sun, or nearly so. The tidal forces of the Sun have over eons of time slowed down the rotation of Mercury to match its revolution around the Sun. The result is that Mercury rotates very slowly. One day on Mercury is about 58-1/2 Earth days long. But while Mercury's days are very long, its revolution around the Sun is rather fast. Mercury can complete one orbit around the Sun in only 88 Earth days. That's just about 3 months here on Earth. This is why Mercury's name is so appropriate. In mythology, Mercury was a speedy messenger, just like the planet's speedy revolution around the Sun. Mercury has no moons.

Venus
The planet Venus has long been one of the most misunderstood of all the inner planets. Like the Earth, Venus has an atmosphere. However, Venus' atmosphere is far thicker than that of the Earth, making it difficult for modern science to penetrate. Interestingly, scientists have recently been able to peek through the thick clouds and get a few glimpses of the surface. There are numerous volcanoes and many mountains that appear misshapen.

There is much we still do not know about how this planet looks and what it is like. However, using special instruments and probes scientists have in recent years unlocked many of the secrets long hidden by this mysterious world. In the 1970s, the Soviet Union actually was able to land more than one probe on the surface of Venus. These scientific probes only lasted a few hours before they were destroyed by the intense heat of the planet. These probes were able to take several pictures and send them back to earth for scientists to study.

The Earth Has a Sister
Venus is in many ways Earth's sister planet. It is almost identical in size, chemistry, gravity and density as the Earth. In other words, Venus is made up of almost the exact same types of materials as the Earth and in about the same amounts. Venus has volcanoes, mountains and sand, just like Earth.

However, if they are twins, then Venus is the evil twin; she is the Earth gone wrong, very wrong. Venus is a deadly world where the surface temperature is hot enough to cook a meal in mere minutes. There is nowhere to hide from this ever present furnace. And with the atmosphere containing mostly carbon dioxide, it makes Venus a highly toxic place. No living thing would ever be able to survive on Venus.

Global Warming
In the early days of Venus' 4 billion year long life, it would have appeared very similar to the Earth. The two would have been almost identical. However, over a period of a few million years, forces on Venus caused it to take a very different course than the Earth.

Venus lies much closer to the Sun than does our planet. That single fact has caused an unstoppable chain of events that doomed Venus to its fiery existence. Owing to its closer proximity to the Sun, Venus' temperature should have been only slightly warmer than that of the Earth. But as the planet warmed, the water evaporated. This increase in water vapor in the atmosphere began a cycle of global warming that could not be stopped. Water vapor is a very effective greenhouse gas. (Greenhouse gas soaks up hot air and prevents it from escaping into space). The increase in water vapor caused the temperature to rise further, which caused more water to evaporate, causing the temperature to climb still further.

Today it is likely that all of Venus' water has evaporated into the atmosphere. This atmosphere effectively traps the Sun's energy causing the surface to burn much hotter than it naturally would. The temperatures on Venus can reach almost 900 degrees Fahrenheit (approx 482 degrees Celsius).

Venus is Dry
The Earth has a protective layer known as the Ozone Layer. This important shield protects the Earth from the Sun's ultraviolet radiation. Venus does not have an ozone layer. As a result, the ultraviolet radiation from the Sun finds its way directly into Venus' atmosphere. Over many billions of years this radiation has slowly broken down water molecules into hydrogen and oxygen. As a result, there is today very little water left on Venus.

Geography
Venus has many, many volcanoes. We don't know for sure, but it is possible that Venus has more volcanoes than any of the other planets in our Solar System. But unlike the volcanoes on Earth that can sometimes erupt in an explosive manner, the volcanoes on Venus are believed to erupt in a less violent way. In fact, it is believed that they don't erupt at all. Instead, it is thought that the lava just slowly flows out onto the surface.

Venus has a few mountainous areas along with extensive flat areas. There are craters and evidence that the surface long ago moved, much like the surface of the Earth moves today. But unlike the Earth's surface, there is no evidence that Venus has a tectonic plate system.

From West to East
If you somehow found a way to survive the scorching heat found on the surface of Venus, you would quickly notice something strange about the days. Aside from the fact that Venus rotates very slowly so that a day on Venus lasts more than 100 Earth days, Venus also rotates in the opposite direction as almost all the other planets.

Instead of the Sun rising in the east and setting in the west, the Sun on Venus would appear to rise in the west and set in the east.

Moons:
Venus has no moons.
 

Earth

The Earth is the biggest of all the terrestrial planets. A terrestrial planet is a dense planet found in the inner Solar System. The diameter of Earth is 7,926 miles. The circumference measured around the equator is 24,901 miles. There are currently almost 7 billion people living on the Earth. About 30% of the Earth's surface is covered with land, while about 70% is covered by oceans.

Our planet is  an oasis of life in an otherwise desolate universe.  The Earth's temperature, weather, atmosphere and many other factors are just right to keep us alive. 

The Earth has one moon. 

Mars
Mars was the Roman god of war and agriculture. It may not seem like these two things go together, but they do. Mars protected those who fought for their communities, and stayed home to raise crops for food. In Greek, Mars was known as Ares.

The Planet
Mars excites scientists because its mild temperament is more like the Earth's than any of the other planets. Evidence suggests that Mars once had rivers, streams, lakes, and even an ocean. As Mars' atmosphere slowly depleted into outer space, the surface water began to permanently evaporate. Today the only water on Mars in either frozen in the polar caps or underground.

You may sometimes hear Mars referred to as the "Red Planet." This is because the surface of Mars is red. If you stood on the surface of Mars, you would see red dirt and rocks everywhere.

Exploration
At first, the only way modern explorers could study Mars was with satellites that would fly close to the surface of Mars and take pictures as it did so. The satellites would then send these pictures back to Earth.

As scientific technology became more advanced, scientists were able to put spacecraft into orbit around the Red Planet. These types of missions allowed scientists and researchers to obtain even more information about Mars.

Then, as technology advanced even more, scientists and researchers were able to actually land spacecraft on the surface of Mars. To learn more about these amazing explorations.

Moons:
Mars has two moons, their names are Deimos and Phobos.

Jupiter
If you traveled to Jupiter on vacation, you would be very heavy. If you weigh 70 pounds (32 kg) on Earth, on Jupiter you would weigh 185 pounds (84 kg). This is because Jupiter is such a large planet and so has more gravity.

The Planet
Jupiter is by far the largest planet in our Solar System. The Earth could fit inside Jupiter more than 1000 times.

Jupiter is a very stormy planet. There are storms found throughout the atmosphere, and most of the storms seem to never end. The many different cloud formations and storms in the atmosphere also make Jupiter a very colorful planet.

Jupiter's great red spot, visible in the picture above to the right, is where a giant storm has been raging for at least 300 years. This red spot is also called "The Eye of Jupiter" because of its shape. This storm's super hurricane winds blow across an area larger than the Earth.

Jupiter is considered a gas giant because it does not have a solid surface. Under its atmosphere is a large liquid ocean of hydrogen and water. What lies in between that ocean and the atmosphere? Actually, there is no in between. The atmosphere slowly gets thicker and thicker until it becomes part of the ocean. In other words, Jupiter's ocean has no surface on which you could float a boat. The sky becomes the ocean.

Rings
Did you know Jupiter has rings? They are faint and are only able to be viewed when Jupiter passes in front of the Sun. This is because the light from the Sun lights them up for us to see here on Earth. There are three rings in all. They are named Gossamer, Main and Halo.

Moons:
Jupiter has 50 official moons and 12 provisional (unofficial) moons. The four largest and most well-known were discovered by Galileo in the year 1610. Their names are Io, Europa, Ganymede and Callisto. Some of the other moons are Adrastea, Ananke, Carme, Elara, Himalia, Leda, Lysithea, Metis, Pasiphae, Sinope, and Thebe.

 

Saturn
Because Saturn is bigger than the Earth, you would weigh more on Saturn than you do here. If you weigh 70 (32 kg) pounds on Earth, you would weigh 74.5 pounds (34 kg) on Saturn. Probably not as much as you thought, right? Keep reading to find out why.

The Planet
In many ways, Saturn is similar to Jupiter, but it is much smaller. It is the second largest planet in our Solar System and it is a gas giant like Jupiter. Under the clouds of methane, hydrogen and helium, the sky gradually turns into liquid until it becomes a giant ocean of liquid chemicals.

Saturn is the least dense planet in our Solar System. It is made up of mostly hydrogen and helium, which are the two lightest elements in the universe and thus make Saturn the lightest planet that we know of. This is why you wouldn't weigh as much on Saturn as you think you would because of its size. And because Saturn is so light, it does not have as much gravity. Interestingly, it is believed Saturn would actually be able to float in water because the hydrogen and helium that make up the planet are so lightweight.

Because Saturn is such a lightweight planet and it spins so fast, Saturn is not perfectly round like most of the other planets. Like Jupiter, Saturn is wider in the middle and more narrow near its top and bottom.

The Rings
Saturn is most well-known for its rings. However, it is not the only planet with rings. Jupiter, Uranus and Neptune also have rings. Saturn is a favorite object for many observers. Its beautiful rings are 169,800 miles wide (approx 273,266 km). But the rings are amazingly thin, estimated to be less than a kilometer thick. That's only a little more than half a mile (0.62 miles to be exact)! The rings are split into categories, Ring A, Ring B, Ring C, Ring D, Ring E, Ring F and Ring G, totaling 7 in all. The rings are not solid but rather are made up of particles of ice, dust and rocks. The rings are held in place around Saturn by the moons that also orbit this large planet. The gravity of these moons also cause the gaps that are seen in between the rings.

Moons:
Saturn has 53 official moons and 9 provisional (unofficial) moons. The most well-known of Saturn's moons is probably Titan. It is the second largest moon in the Solar System next to Jupiter's Ganymede. Titan is larger than the planet Mercury. Some of the other moons are Atlas, Calypso, Dione, Enceladus, Hyperion, Iapetus, Janus, Mimas, Phoebe, and Tethys.

 

 

Uranus
It would take you many years to fly a rocket to Uranus. When you arrived you would weigh less because Uranus' gravity is not as strong as the Earth's. If you weigh 70 pounds (32 kg) on Earth, you would weigh 62 pounds (28 kg) on Uranus.

The Planet
Like Jupiter and Saturn, Uranus is a gas giant. But Uranus is a little different. Unlike all the other planets and most of the moons in our Solar System, Uranus spins on its side. It is believed that long ago a very large object smashed into this planet. The crash was so powerful that it completely changed the direction of Uranus' planetary rotation. However, a more recent theory is that the extreme tilt of Uranus' axis may have been caused by a large moon that was slowly pulled away from the planet by another large planet long ago when our Solar System was still new. It is thought that the gravitational pull of this moon moving away from Uranus may have caused it to tilt on its side.

Like Saturn, the thick atmosphere of Uranus is made up of methane, hydrogen and helium. But Uranus is an extremely cold planet. It has been called the "ice giant." It is believed that Uranus is made up of rock and ice and has a large rocky core. Because of the tremendous planetary pressure of Uranus, there could possibly be trillions of large diamonds in or on the surface of this planet.

Scientists also believe that on the surface of Uranus there may be a huge ocean. And, interestingly, it is thought that the temperature of this ocean may be extremely hot, maybe even as hot as 5000 degrees Fahrenheit (2760 Celsius).

Uranus is almost identical to the planet Neptune.

Rings
Uranus also has rings, though they don't stretch out as far as the rings of Saturn. The rings of Uranus are made up of black dust particles and large rocks.

Moons:
Uranus has 27 moons. Five of these moons are large and the rest are smaller. The largest moon is Titania, followed by Oberon, Umbriel, Ariel and Miranda. Some of the smaller moons are named: Belinda, Bianca, Caliban, Cordelia, Cressida, Desdemona, Juliet, Ophelia, Portia, Puck, and Rosalind.

 

Neptune 
For many, centuries people did not know that this planet even existed. It was discovered by Johann Galle and Heinrich D'Arrest in 1846.

Neptune is the smallest of the four gas giants in our Solar System. Much like Saturn and Uranus, Neptune's atmosphere contains hydrogen, helium and methane.

Not much was known about Neptune until it was visited by the spacecraft Voyager 2 on August 25, 1989. Voyager 2 took many pictures of the planet, and much of what we know today about Neptune came from this single visit. These pictures show a brilliant blue planet with a few thin white clouds laced around its surface.

In Neptune's atmosphere, there is a large white cloud that moves around rather quickly. The "scooting" of this cloud around the atmosphere has led it to be named "Scooter."

When Voyager 2 visited Neptune, its pictures showed a giant storm much like the storm on Jupiter. This storm is called the "Great Dark Spot" because it appears as a dark oval shape on the surface of the planet. We do not know how long this storm has been active or if it is still present. More recently, the Hubble Space Telescope sent pictures back to Earth and there was no sign of the Great Dark Spot. These pictures did show two other dark spots that eventually faded away.

Neptune is a very windy place. No other planet in the Solar System has winds that are as strong as Neptune's. The winds near the Great Dark Spot were believed to have reached nearly 1,200 miles per hour (approx 1931 km per hour). Perhaps this extremely windy atmosphere contributes to the appearance and disappearance of the great dark spots.

Rings
Neptune has six rings which circle the planet. These rings are believed to be fairly new. The rings are more irregular than the rings of other planets. There are areas of varying thickness throughout the rings.

Moons:
Neptune has 13 moons that we know of. Because Neptune is so far away, it is difficult to see any of these worlds. There are probably many more moons orbiting this blue planet which we have not yet discovered. Perhaps you will be the astronomer who discovers some of these worlds. The first moon to be discovered was Triton. Triton was discovered by an amateur astronomer in England named William Lassell only 17 days after Neptune was discovered in 1846. The names of the other moons are: Despina, Galatea, Halimede, Laomedeia, Larissa, Naiad, Nereid, Neso, Proteus, Psamathe, Sao, and Thalassa.

Asteroids
An asteroid is a large rock in outer space. Some, like Ceres, can be very large, while others are as small as a grain of sand. Due to their smaller size, asteroids do not have enough gravity to pull themselves into the shape of a ball.  Astronomers group asteroids into different categories based on the way they reflect sunlight.

There are 26 very large asteroids have been discovered, which is probably most of the big ones. But there are still millions of smaller ones that we have yet to see because they are too tiny, only a mile or so across.

 

Comet

A comet is a small world which scientists sometimes call a planetesimal. They are made out of dust and ice, kind of like a dirty snow ball. Comets come from two places:  The Kuiper Belt and the Oort Cloud. 

Imagine a place far, far away at the very edge of the Solar System. A place where millions of comets can be seen swishing around in every direction. These icy comets are orbiting the Sun in two different places, both of which are very distant.  One place is called the Oort cloud, and the other is called the Kuiper Belt.
A comet will spend billions of years in the Kuiper Belt or Oort Cloud.  Sometimes two comets will come very close to each other, or even crash into one another.  When this happens the comets change directions.  Sometimes their new path will bring them into the Inner Solar System.

This is when a comet begins to shine. Up until now the comet has been among millions of others exactly the same, but as they approach the warmer Inner Solar System they begin to melt leaving behind magnificent tails.

Unfortunately, comets don't live very long once they enter the warmer part of the Solar System. Just like a snowman melts in the summer, comets melt in the Inner Solar System.   Although it is the most glorious part of their lives, traveling through the Inner Solar System eventually kills them.  After several thousand years they melt down to a little bit of ice and dust, not nearly enough to leave a tail. Some even melt away completely. 

Meteorits 

You have probably heard of a shooting or falling star, but have you ever seen one? If you have ever spent any amount of time looking up at the night sky, then you probably have - a flash of light streaking high above through the darkness for just a moment, disappearing just as quickly as it appeared - sometimes so quick that you cannot be sure if you have really seen something or imagined it. You might think that your eyes are playing tricks on you, but shooting stars are definitely real! Your parents may have told you to quickly make a wish on a shooting star before it vanishes - what will your next wish be when you get to see one?

Here’s another question for you, a little bit harder this time: do you know what a shooting star is? Their names are a little misleading and this causes some people to think that these fast moving trails of light really are stars that have fallen out of the sky. However, this is not true. Our Sun is a star, our closest star, and the other stars are many many miles away (it would take more than your lifetime to travel to them!) and since they are much bigger than a shooting star, they are certainly not responsible, so we can count them out. If you are still not sure of the answer, then you might be surprised to learn that shooting stars are just tiny bits of dust entering the Earth’s atmosphere from space. Tiny particles, like grains of sand or pebbles on a beach, like to crash into the atmosphere at amazingly fast speeds - some faster than a car travelling at his highest speed along the motorway! But don’t worry - they are not big enough to harm you! If you pick up a stone from the beach, however, you will find that a fast moving pebble does not quite look the same as a shooting star, no matter how hard you throw it. This is because the light that you see is the heat of the air around them as they fly into the atmosphere and burn up.

 

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OPTIC

EYES

The eye is one of the most complex parts of the body. The different parts of the eye allow the body to take in light and perceive objects around us in the proper color, detail and depth. This allows people to make more informed decisions about their environment. If a portion of the eye becomes damaged, you may not be able to see effectively, or lose your vision all together. Eyes are one of the five senses which is the only means of optical natural living things. Optical instrument is not God's gift to the less sophisticated tools of modern optics. The lens in our eye is the fastest lens when focusing an object to make it look obvious. There is no one tool that could rival any speed created an object. 

 

There are several physical and chemical elements that make up the eye. The eye is also heavily involved with the nervous system, which allows the brain to take in information from the eyes and make the appropriate decisions on how to act upon this information. The nerves must be kept in prime condition or the brain may start to receive false images, or you will not take in enough information to get an accurate perception of your environment.

Eye Parts	Description and Functions
Cornea	The cornea is the outer covering of the eye. This dome-shaped layer protects your eye from elements that could cause damage to the inner parts of the eye. There are several layers of the cornea, creating a tough layer that provides additional protection. These layers regenerate very quickly, helping the eye to eliminate damage more easily. The cornea also allows the eye to properly focus on light more effectively. Those who are having trouble focusing their eyes properly can have their corneas surgically reshaped to eliminate this problem.
Sclera	The sclera is commonly referred to as the "whites" of the eye. This is a smooth, white layer on the outside, but the inside is brown and contains grooves that help the tendons of the eye attach properly. The sclera provides structure and safety for the inner workings of the eye, but is also flexible so that the eye can move to seek out objects as necessary.
Pupil	The pupil appears as a black dot in the middle of the eye. This black area is actually a hole that takes in light so the eye can focus on the objects in front of it.
Iris	The iris is the area of the eye that contains the pigment which gives the eye its color. This area surrounds the pupil, and uses the dilator pupillae muscles to widen or close the pupil. This allows the eye to take in more or less light depending on how bright it is around you. If it is too bright, the iris will shrink the pupil so that they eye can focus more effectively.
Conjunctiva Glands	These are layers of mucus which help keep the outside of the eye moist. If the eye dries out it can become itchy and painful. It can also become more susceptible to damage or infection. If the conjunctiva glands become infected the patient will develop "pink eye."
Lacrimal Glands	These glands are located on the outer corner of each eye. They produce tears which help moisten the eye when it becomes dry, and flush out particles which irritate the eye. As tears flush out potentially dangerous irritants, it becomes easier to focus properly.
Lens	The lens sits directly behind the pupil. This is a clear layer that focuses the light the pupil takes in. It is held in place by the ciliary muscles, which allow the lens to change shape depending on the amount of light that hits it so it can be properly focused.
Retina	The light focuses by the lens will be transmitted onto the retina. This is made of rods and cones arranged in layers, which will transmit light into chemicals and electrical pulses. The retina is located in the back of the eye, and is connected to the optic nerves that will transmit the images the eye sees to the brain so they can be interpreted. The back of the retina, known as the macula, will help interpret the details of the object the eye is working to interpret. The center of the macula, known as the fova will increase the detail of these images to a perceivable point.
Ciliary Body	Ciliary body is a ring-shaped tissue which holds and controls the movement of the eye lens, and thus, it helps to control the shape of the lens.
Choroid	The choroid lies between the retina and the sclera, which provides blood supply to the eye. Just like any other portion of the body, the blood supply gives nutrition to the various parts of the eye.
Vitreous Humor	The vitreous humor is the gel located in the back of the eye which helps it hold its shape. This gel takes in nutrients from the ciliary body, aqueous humor and the retinal vessels so the eye can remain healthy. When debris finds its way into the vitreous humor, it causes the eye to perceive "floaters," or spots that move across the vision area that cannot be attributed to objects in the environment.
Aqueous Humor	The aqueous humor is a watery substance that fills the eye. It is split into two chambers. The anterior chamber is located in front of the iris, and the posterior chamber is directly behind it. These layers allow the eye to maintain its shape. This liquid is drained through the Schlemm canal so that any buildup in the eye can be removed. If the patient's aqueous humor is not draining properly, they can develop glaucoma.

  

The Image Formation in eyes

Our eyes can see when there are objects that reflect light entering the eye. The light is then refracted by the lens of the eye so that the image formed on the retina. The image formed by the lens of the eye is real inverted and scaled. The shadow is then transmitted to the brain by the optic nerve so that we can see and respond. Here's an illustration of the formation of the optical instrument . 

Accommodation power   

The distance between the lens of the eye is the retina remains will never change unless permanent damage. To see objects lying fickle, convex eyepiece should be changed. By changing the curvature of the lens is to change the distance of the lens focus. When the eyes see objects that are far away, the eye muscles are relaxed and the lens of the eye becomes more flat (thinning). Conversely, when the eyes see objects that are very close, in a state of contraction of the eye muscles and eye lenses become more convex (thicken). Thickening and thinning is intended that the eye shadow can fall right in retina so it can be seen clearly. Well, the ability to thicken and the depletion of the eye lens is called the power of accommodation of the eye.

PP and PR

Optical devices have a restricted range of eye see objects. We know there is much point his name near the eye and the eye point. Eyes Far point (punctum remotum) is the furthest point of the eye that can still be seen with the eye in a state of berakomodasi. Near the eye point (punctum proximum) is the closest point of the eye that can still be seen clearly by eye in a state of maximum accommodation. Normally a point distant normal adults is not infinite and the closest point is 25 cm. If a point distant or near the point of no longer seseuai with normal size then the sign of optical instruments naturally we experienced eye defects. There is a picture that show the PP and PR in different eyes.

 

Disorders of the Eye

Refractive errors of the eye are seen in 20 percent of children and have been found to run in families. The most common refractive errors are astigmatism, hyperopia (farsightedness) and myopia (nearsightedness).

11.  Hyperopia

Hyperopia is a condition in which an image of a distant object becomes focused behind the retina; making objects up close appear out of focus. The characteristics of patients with nearsightedness is he cannot see clearly objects that are located close eye though was maximum accommodation. The cause is not the eye lens can become convex properly so that the rays from close objects will cast a shadow in the back of the retina. People with nearsightedness can be helped by using glasses (optical instrument) or positive convex lens. The power of the lens that can be used depending on the patient hyperopia point near the patient. In order to view objects at a normal reading distance (25 cm), then the patient must use a farsighted eyeglass lenses that produce shadows in front of the lens at a distance equal to a point near the patient

12. Myopia

      Myopia is a condition in which, opposite of hyperopia, an image of a distant object becomes focused in front of the retina, making distant objects appear out of focus. Myopia is the most common refractive error seen in children and can be corrected with eye glasses or contact lenses. A person who has a disability eye nearsighted cannot see distant objects clearly. This eye defect caused the eye lens cannot be flattened well so that parallel rays coming from objects falling in front of the retina. Point the patient is far less than infinity. People with nearsightedness (myopia) can be helped by using glasses with concave lenses or negative. The amount of lens power (diopters) used very nearsighted patients far point depend on the patients. In order to see objects at a distance of infinity as normal eye, nearsighted patients should use a concave lens which produces a shadow in front of the lens at a distance equal to the far point the patient. So the distance of virtual shadow is formed s’ = point away patients

 3. Astigmatism 

 Astigmatism is a condition in which an abnormal curvature of the cornea can cause two focal points to fall in two different locations, making objects up close and at a distance appear blurry. People with astigmatism are not able to see the lines and vertical horizontal together. The reason is the shape of the cornea is not spherical but rather curved in one area than in other areas. Astigmatism suffers can be helped with optical instrument such as silindris lens. Only an eye care professional can accurately detect, diagnose and treat astigmatism. That's why it's so important to test children who may not know they're having a vision problem, and why routine comprehensive eye care exams are vital to maintaining healthy vision and healthy sight. Astigmatism treatments help the eyes focus images correctly on the retina at near, middle and far distances. This can be accomplished through prescription eyeglasses, contact lenses or in some instances, through the use of surgery that reshapes the cornea of the eye. Each astigmatism treatment option has benefits and drawbacks that should be discussed completely with an eye care professional.

 

14. Presbyopia

In Presbyopia, a person’s eye progressively diminishes in its ability to focus on near objects with age. The exact mechanism that causes this “loss” in focusing ability is not completely proven. However, most researchers believe that the crystaline lens inside the eye loses its flexibility with age as an early cataract begins to form. It is a defect of the eye in which sufferers have not been able to see well objects at a great distance and very close. Patients have much less than infinite point and near point greater than 25 cm. This loss in flexibility directly causes a loss in person’s ability to focus. Similar to grey hair, presbyopia is a symptom that everyone experiences as they age. The first symptoms are usually noticed by 38 years of age and present to us as headaches.

Treatment for presbyopia has advanced significantly in recent years with many options now available to our patients. Some of the following options you may find helpful as follows.

1.      Reading Glasses

Over the counter reading glasses are sold to many people in drug stores, and in dollar stores. They are an effective form of treatment for people who see well in the distance. Of course, these do not work for near sighted individuals, and only work well for far sighted individuals who have small degrees of far sightedness.

2.      Contact Lenses

This is a very effective form of treatment that can be tried during a contact lens examination

3.      Bifocal Glasses

This works very well for most people. The top portions of the glasses are for seeing in the distance and the bottom portions of the lenses are for seeing up close. The two main types of bifocal glasses are glasses with and without a line. A progressive addition lens does not have a line. Lots of people prefer the “no line” or progressive lens because it is cosmetically pleasing. However, we prefer the lined bifocal because it is easier for a patient to adapt too. During the routine eye examination, a prescription is always given to the patient, and bifocal glasses are an excellent option for glasses. 

 

 

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