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, Construction working, uses, ray diagram
Simple Telescope
A simple working telescope requires nothing more than a pair of lenses mounted in a tube. The lens in front, known as the objective, focuses an image; the lens in back, known as the eyepiece, magnifies the image. Although it may seem like a crude device, a simple telescope nicely illustrates the basic working principles of more powerful astronomical instruments.
LENSES
Light normally moves in straight lines, but there are situations in which this is not true. You are already familiar with some: for example, the distortions you see looking through the surface of the ocean occur because light bends as it passes from the water into the air. Long before we understood why light bends as it passes from one transparent material to another, people had used this effect to create lenses: optical devices which can gather light together or spread it apart.
In order to understand how a lens works, you need to know a little about how light behaves in passing from one material to another. Imagine a tank of water on the table in front of you; the surface of the water should be perfectly flat and horizontal. If you shine a ray of light straight down from above, it will pass through the surface of the water without bending. But if you shine the light in at an angle, it will bend as it passes through the surface. Fig. 1 illustrates two important facts about this effect. First, in passing from air to water, the light always bends into the water. Second, the smaller the angle between the light ray and the surface, the more it bends in passing through. The same rules would also apply if the tank of water was replaced with a block of glass.
To create a lens which can focus many parallel rays of light to a single point, the idea is to curve the surface of the glass so that all these rays, after passing through, come together at the same place. It's a bit tricky to do this right, but we don't need to worry about the details. The simplest kind of lens is a `plano-convex' lens; one side is flat, while the other bulges out at the middle. Fig. 2 shows how such a lens focuses light. The optical axis of the lens is the thick line which passes right through the middle of the lens; a ray of light traveling along the optical axis is not bent at all. Rays which pass through the top of the lens are bent downward, while rays which pass through the bottom of the lens are bent upward. Thus all these light rays are bent toward the optical axis. If the lens is well-made, all rays meet at the same focal point. The distance between the lens and the focal point, measured along the optical axis, is called the focal length.
A simple lens in operation. Parallel light rays come from the right, pass through the lens, and meet at the focal point on the left. The thick line through the middle of the lens is the optical axis; the distance F is the focal length.
Image formation
A lens which could only focus light rays striking the glass head-on (as in Fig. 2) would be fairly useless for astronomy. Fortunately, most lenses can also accept rays which come in at a slight angle to the optical axis, and bring them to a focus as well. This focal point is not the same as the focal point for rays which are parallel to the optical axis; depending on the angle of the incoming rays, their focus lies on one side or the other of the optical axis, as shown in figure. But if the lens is well-made, all these focal points will lie on a plane which is parallel to the face of the lens; this is called the focal plane.
A simple lens forming an image. The red rays arrive with an downward slant, and come to a focus below the optical axis, while the blue rays arrive with a upward slant, and come to a focus above the optical axis. The vertical dotted line at left represents the focal plane.
There's one slightly subtle consequence of this image-formation process: the image is upside-down! Fig. 4 shows why: rays from the lower part of the subject (on the right) come together at the upper part of the image (left), and vice versa. This is also true of a camera; of course, you turn the prints right way up when you get them back from the store, so you're probably not aware that the image is upside down inside your camera.
The image formed by a simple lens is upside-down with respect to the subject. Here the subject (right) is an arrow with a red tip pointing upward; its image (left, at the focal plane) points down.
EYEPIECES AND MAGNIFICATION
To make a telescope you can actually look through, you'll need to add another lens. This eyepiece lens magnifies the image formed by the large objective lens and directs the light to your eye. Basically, the eyepiece works a lot like a magnifying glass; it enables your eye to focus much more closely than it normally can. The eyepiece on a typical telescope allows you to inspect the image formed by the objective lens from a distance of an inch or less. Fig. 5 shows how the objective lens and eyepiece work together in a simple telescope.
The magnification of a telescope is easy to calculate once you know the focal lengths F and f of the objective lens and eyepiece, respectively. The formula for the magnification M is
M = F ÷ f
Here you can use any units for F and f, as long as you use the same units for both. For example, if you measure F in millimeters, you should also measure f in millimeters. Using the values for F and f you measured above, calculate the expected magnification of your telescope.
To measure the magnification of your telescope directly, we will set up a target – basically a picture of a ruler with marks a unit distance apart. From the other end of the room, focus your telescope on the target. Now look through the telescope while keeping both eyes open; you should see a double image, where one image is magnified and the other is not. Compare the two images; how many of the unmagnified units fit within one magnified unit? The answer is a direct measurement of your telescope's magnification; record it in your notebook and compare it to the magnification you calculated using the formula above.
Astronomical telescope
An astronomical telescope is an optical instrument which is used to see the magnified image of distant heavenly bodies like stars, planets, satellites and galaxies etc. The final image formed by an astronomical telescope is always virtual, inverted and magnified.
Principle of Astronomical Telescope
An astronomical telescope works on the principle that when an object to be magnified is placed at a large distance from the objective lens of telescope, a virtual, inverted and magnified image of the object is formed at the least distance of distinct vision from the eye held close to the eye piece.
Construction of Astronomical Telescope
An astronomical telescope consists of two convex lenses : an objective lens O and an eye piece E. the focal length fo of the objective lens of astronomical telescope is large as compared to the focal length fe of the eye piece. And the aperture of objective lens O is large as compared to that of eye piece, so that it can receive more light from the distant object and form a bright image of the distant object. Both the objective lens and the eye piece are fitted at the free ends of two sliding tubes, at a suitable distance from each other.
Working of Astronomical telescope
The ray diagram to show the working of the astronomical telescope is shown in figure. A parallel beam of light from a heavenly body such as stars, planets or satellites fall on the objective lens of the telescope. The objective lens forms a real, inverted and diminished image A’B’ of the heavenly body. This image (A’B’) now acts as an object for the eye piece E, whose position is adjusted so that the image lies between the focus fe’ and the optical centre C2 of the eye piece. Now the eye piece forms a virtual, inverted and highly magnified image of object at infinity. When the final image of an object is formed at infinity, the telescope is said to be in ‘normal adjustment’.
It should be noted that, the final image of object (such as stars, planets or satellites) formed by an astronomical telescope is always inverted with respect to the object. But it does not matter whether the image formed by an astronomical telescope is inverted or not, as all the heavenly bodies are usually spherical is shape.
Magnifying Power of an Astronomical Telescope
The Magnifying Power of a telescope is given by:
m = 
Magnifying Power of an Astronomical Telescope
Where, fo = Focal length of the objective lens
fe = Focal length of the eye-piece lens
And the length (L) of the tube of telescope is equal to the sum of the focal lengths of the objective lens and the eye piece. Thus, L = fo + fe
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A telescope is an optical instrument that makes distant objects appear closer. Telescopes are used for a variety of purposes, including astronomy, navigation, and surveillance.
There are two main types of telescopes: refracting telescopes and reflecting telescopes. Refracting telescopes use lenses to bend and focus light, while reflecting telescopes use mirrors.
Refracting telescopes were the first type of telescope to be invented. They were invented in the early 1600s by Hans Lippershey and Zacharias Janssen. Refracting telescopes are relatively simple to make and use, but they have a few limitations. One limitation is that they can only be used to view objects that are above the horizon. Another limitation is that they can suffer from chromatic aberration, which is a distortion of colors that can make images appear blurry.
Reflecting telescopes were invented in the late 1600s by Isaac Newton. Reflecting telescopes are more complex to make than refracting telescopes, but they have several advantages. One advantage is that they can be used to view objects that are below the horizon. Another advantage is that they do not suffer from chromatic aberration.
There are several different types of reflecting telescopes. The most common type is the Newtonian telescope, which uses a primary mirror to reflect light to a secondary mirror that then reflects it to the eyepiece. Other types of reflecting telescopes include the Cassegrain telescope, the Schmidt-Cassegrain telescope, and the Maksutov-Cassegrain telescope.
Catadioptric telescopes are a type of telescope that uses both lenses and mirrors. The most common type of catadioptric telescope is the Schmidt telescope, which uses a spherical primary mirror and a corrector plate to correct for spherical aberration. Other types of catadioptric telescopes include the Maksutov telescope and the Ritchey-Chrétien telescope.
Active optics telescopes are a type of telescope that uses computers to control the shape of the primary mirror in order to compensate for atmospheric turbulence. Adaptive optics telescopes are a type of telescope that uses a deformable mirror to correct for atmospheric turbulence in real time. Extremely large telescopes are a type of telescope that have a primary mirror that is larger than 10 meters in diameter.
Telescopes have played a major role in the advancement of astronomy. They have allowed astronomers to see objects that are too faint or too far away to be seen with the naked eye. Telescopes have also allowed astronomers to study the universe in great detail.
Telescopes are an essential tool for astronomers, and they have helped us to learn a great deal about the universe.
What is a telescope?
A telescope is an optical instrument that makes distant objects appear closer. Telescopes use lenses or mirrors to collect light and focus it on a small area, making the image appear larger.
What are the different types of telescopes?
There are two main types of telescopes: refracting telescopes and reflecting telescopes. Refracting telescopes use lenses to collect and focus light, while reflecting telescopes use mirrors.
What are the advantages and disadvantages of each type of telescope?
Refracting telescopes are generally easier to use than reflecting telescopes, but they are also more expensive. Reflecting telescopes are less expensive than refracting telescopes, but they can be more difficult to use.
What are some of the most important features to consider when choosing a telescope?
The most important features to consider when choosing a telescope are the aperture, the magnification, and the field of view. The aperture is the diameter of the main lens or mirror in the telescope. The larger the aperture, the more light the telescope can collect and the brighter the image will be. The magnification is the ability of the telescope to make objects appear larger. The higher the magnification, the larger the object will appear in the eyepiece. The field of view is the amount of sky that can be seen at once through the telescope. A wider field of view is useful for observing large objects, such as planets and galaxies.
How do I use a telescope?
To use a telescope, first find a comfortable position to stand or sit in. Then, hold the telescope up to your eye and look through the eyepiece. You may need to adjust the focus knob to get a clear image. Once you have a clear image, you can use the telescope to observe distant objects.
What are some of the things I can see with a telescope?
With a telescope, you can see a variety of objects, including planets, stars, galaxies, and nebulae. You can also use a telescope to observe the Moon and the Sun.
What are some of the safety precautions I should take when using a telescope?
When using a telescope, it is important to take safety precautions to protect your eyes and your telescope. First, never look directly at the Sun with a telescope. The Sun’s light can damage your eyes. Second, always use a sun filter when observing the Sun. Third, never point a telescope at anything that could be dangerous, such as a power line or a moving vehicle.
Where can I learn more about telescopes?
There are many Resources available to learn more about telescopes. You can find books, websites, and even online courses on the subject. You can also visit a local astronomy club or observatory to learn more about telescopes and astronomy.
- A telescope is an optical instrument that makes distant objects appear closer.
- The two main types of telescopes are refracting telescopes and reflecting telescopes.
- Refracting telescopes use lenses to bend and focus light, while reflecting telescopes use mirrors to do the same.
- The main advantage of refracting telescopes is that they are relatively easy to make and use.
- The main advantage of reflecting telescopes is that they can be made larger than refracting telescopes.
- The largest telescope in the world is the Gran Telescopio Canarias, which is located in the Canary Islands.
- The Gran Telescopio Canarias has a primary mirror that is 10.4 meters in diameter.
- The Gran Telescopio Canarias is used to study objects in space, such as stars, galaxies, and planets.
- The Hubble Space Telescope is a space telescope that was launched in 1990.
- The Hubble Space Telescope has a primary mirror that is 2.4 meters in diameter.
- The Hubble Space Telescope is used to study objects in space, such as stars, galaxies, and planets.
- The Hubble Space Telescope has made many important discoveries, such as the expansion of the universe and the existence of dark matter.
- The James Webb Space Telescope is a space telescope that is scheduled to be launched in 2021.
- The James Webb Space Telescope will have a primary mirror that is 6.5 meters in diameter.
The James Webb Space Telescope will be used to study objects in space, such as stars, galaxies, and planets.
The first telescope was invented in the early 1600s by Hans Lippershey.
- Lippershey was a Dutch spectacle maker who accidentally invented the telescope while trying to make a new type of eyeglasses.
- Galileo Galilei was one of the first people to use a telescope to study the sky.
- Galileo made many important discoveries with his telescope, such as the four largest moons of Jupiter and the phases of Venus.
- Isaac Newton invented the reflecting telescope in the late 1600s.
- Newton’s reflecting telescope was much more powerful than the refracting telescopes that were available at the time.
- Newton’s reflecting telescope allowed astronomers to see objects in space that were previously invisible.
- The invention of the telescope revolutionized astronomy and led to many important discoveries about the universe.
- Telescopes are still used by astronomers today to study objects in space.
Telescopes have helped us to learn a great deal about the universe, and they will continue to be an important tool for astronomers in the future.
What is the main purpose of a telescope?
(A) To make distant objects appear closer.
(B) To study objects in space.
(C) To make objects in space appear larger.
(D) To make objects in space appear brighter.What are the two main types of telescopes?
(A) Refracting telescopes and reflecting telescopes.
(B) Optical telescopes and radio telescopes.
(C) Ground-based telescopes and space telescopes.
(D) Large telescopes and small telescopes.What is the main advantage of refracting telescopes?
(A) They are relatively easy to make and use.
(B) They can be made larger than reflecting telescopes.
(C) They can see objects in space that are invisible to reflecting telescopes.
(D) They are more accurate than reflecting telescopes.What is the main advantage of reflecting telescopes?
(A) They are relatively easy to make and use.
(B) They can be made larger than refracting telescopes.
(C) They can see objects in space that are invisible to refracting telescopes.
(D) They are more accurate than refracting telescopes.What is the largest telescope in the world?
(A) The Gran Telescopio Canarias.
(B) The Hubble Space Telescope.
(C) The James Webb Space Telescope.
(D) The Keck Telescope.The Hubble Space Telescope is a space telescope that was launched in
(A) 1990.
(B) 1995.
(C) 2000.
(D) 2005.The Hubble Space Telescope has a primary mirror that is
(A) 2.4 meters in diameter.
(B) 4 meters in diameter.
(C) 6.5 meters in diameter.
(D) 10 meters in diameter.