The Optical Telescope
A telescope that is optical is a telescope that gathers and focuses light very keenly. It is mainly from the parts that are visible of the electromagnetic spectrum. That is to create a magnified image for the direct view or to make a photograph or we can say to collect data through electronic sensor image.
There are said to be three primary types of optical telescope that are:
The refractors which use lenses are dioptrics.
The reflectors that use mirrors are catoptrics.
The catadioptric telescopes combine lenses and mirrors.
Reflecting Telescope
Telescope is a device that is used to form magnified images of objects that are distant. The telescope is said to be undoubtedly the most important investigative tool in astronomy. It provides a means of collecting as well as analyzing radiation which comes from celestial objects, even those which are in the far reaches of the universe.
The term is Galileo astronomy that was revolutionized when he applied the telescope to the study of extraterrestrial bodies in the early 17th century.
Until then instruments magnification had never been used for this purpose. Since the work of Galileo’s pioneering that is increasingly more powerful optical telescopes which have been developed till date. We can say that as it has a wide array of instruments that is capable of detecting and measuring radiation in every region of the electromagnetic spectrum. The capabilities which are observational have been further enhanced by the invention of various kinds of instruments that are auxiliary that is the camera, spectrograph, and charge-coupled device and by the use of the electronic computers, the rockets, and spacecraft in conjunction with the system that is the telescope.
Astronomical Telescope
The telescope astronomer makes use of two lenses that are positive lenses: the objective, which usually forms the image of the object which is distant at its focal length. And the eyepiece that generally acts as a simple magnifier with which to view the image that is formed by the objective.
Its length is said to be equal to the sum of the focal lengths of the objective and eyepiece as well. And its angular magnification which is written as -fo /fe , giving an inverted image.
The telescope that is astronomical which can be used for terrestrial viewing but seeing the image that is in the position of upside down is a definite inconvenience. By viewing stars upside down direction there is no problem. A shorter telescope that is with upright viewing is said to be the Galilean telescope.
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Types of Reflecting Telescopes
A telescope that is the reflecting one also known as a reflector is a telescope that uses a single or is a combination which is of curved mirrors that reflect light and form an image. The telescope which is reflecting was invented in the 17th century by sir Isaac Newton as an alternative to the refracting telescope. Which at that time was a design which suffered from severe aberration chromaticity. Although the telescope that is reflecting one produces other types of optical aberrations.
It is a design that usually allows for very large objective diameter. Almost all of the major telescopes which are used in astronomy research are said to be reflectors.
The telescope which is reflecting comes in many designs and variations and may employ some extra elements that are optical to improve the image quality or we can say the place in the image in a mechanically position that is advantageous. Since the telescope that is reflecting use mirrors the design is sometimes referred to as the term "catoptric" telescope.
A primarily curved mirror is the telescope which is a reflector basic optical element that creates an image at the focal plane. The distance that is from the mirror to the focal plane is known as the focal length. The film or we say that a digital sensor may be located here to record the image easily or a secondary mirror which may be added to modify the optical characteristics or redirect the light to film. The digital sensors, or any other eyepiece for visual observation.
The telescope that is the reflecting is just like any other optical system that generally does not produce "perfect" images. The need to image objects which are at distances up to infinity is to view them at different wavelengths of light. Which is along with the requirement to have some way to view the image the mirror produces. This means that there is always some compromise in a reflecting telescope's optical design.
Non Optical Telescopes
We notice that until the 1930’s all the observations astronomical had been made in the visible region of the spectrum that is the electromagnetic one. Although there are some of the scientists who had predicted that some objects in space should produce a spectrum that is continuous beyond the visible and yet no one had observed them. The discovery of the radio which was extraterrestrial sources was made by accident by Karl Jansky who was working for the famous Bell Laboratories in 1933.
It was said that he was investigating a source of radio interference in short-wave radio transmissions that took across the Atlantic ocean. This was happening when he discovered that the noise was coming from the direction of the centre of the Milky way in the constellation Sagittarius. The first purpose that was for building a radio-telescope for observing radio sources emanating from space was in 1937. And since that time the field of astronomy which is of radio has become a fundamental area of research.
FAQs on Optical Telescope
1. What is an optical telescope and what is its primary function in astronomy?
An optical telescope is an instrument designed to gather and focus light, primarily from the visible light portion of the electromagnetic spectrum. Its main purpose is to create a magnified image of distant celestial objects, such as stars, planets, and galaxies, allowing us to see them in much greater detail than is possible with the naked eye.
2. What are the three main designs of optical telescopes?
The three principal designs of optical telescopes are distinguished by how they collect and focus light:
- Refracting Telescopes (Dioptrics): These use a large convex lens, known as the objective lens, to bend or refract light to a focal point.
- Reflecting Telescopes (Catoptrics): These use a large, curved primary mirror to collect and reflect light to a focal point.
- Catadioptric Telescopes: These are hybrid designs that use a combination of both lenses and mirrors to form an image, correcting for optical errors found in the other two types.
3. How does a refracting telescope form an image of a distant object?
A refracting telescope works by using a large objective lens at the front to gather light from a distant object. This lens bends the parallel light rays, bringing them to a focus to form a real, inverted image. A second, smaller lens called the eyepiece is then used to magnify this initial image, allowing the observer to see a larger, more detailed view.
4. What are the key components of a reflecting telescope, such as the Cassegrain design?
A reflecting telescope's main components are mirrors. It uses a large, concave primary mirror at the back of the tube to collect and focus light. Before the light reaches a focal point, a smaller secondary mirror intercepts it and reflects it towards an eyepiece, which is often located through a hole in the primary mirror in the popular Cassegrain design. This setup allows for a more compact and powerful instrument.
5. What is meant by the 'magnifying power' of a telescope and how is it determined?
The magnifying power of an astronomical telescope is a measure of how much larger it can make an object appear. It is defined as the ratio of the focal length of the objective lens (f₀) to the focal length of the eyepiece lens (fₑ). The formula is M = f₀ / fₑ. Therefore, a longer objective focal length and a shorter eyepiece focal length result in higher magnification.
6. Why are most modern, large astronomical observatories built with reflecting telescopes instead of refracting ones?
Modern research telescopes are predominantly reflectors for several critical reasons:
- Absence of Chromatic Aberration: Mirrors reflect all wavelengths of light equally, so they do not suffer from the colour fringing (chromatic aberration) that occurs in lenses.
- Structural Support: A large mirror can be supported across its entire back surface, allowing for the construction of much larger and heavier objectives than lenses, which can only be supported at their edges.
- Cost and Manufacturing: It is technically easier and less expensive to manufacture a large, high-quality mirror than a large, flawless lens.
7. Where are some major optical telescopes located in India?
India is home to several world-class optical observatories. Notable examples include the 3.6m Devasthal Optical Telescope near Nainital, operated by ARIES, which is the largest in Asia. Another significant facility is the Indian Astronomical Observatory in Hanle, Ladakh, situated at a high altitude for clearer skies. The Vainu Bappu Observatory in Kavalur, Tamil Nadu, also houses several important telescopes.
8. How does an optical telescope fundamentally differ from a radio telescope?
The fundamental difference lies in the type of electromagnetic radiation they are designed to detect. An optical telescope collects and focuses visible light, the same light our eyes can see. A radio telescope, on the other hand, uses a large dish antenna to collect much longer wavelength radio waves emitted by celestial objects. This allows astronomers to study different cosmic phenomena, such as the cold gas between stars, which are invisible to optical telescopes.
