1.
Telescope mount
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A telescope mount is a mechanical structure which supports a telescope. Telescope mounts are designed to support the mass of the telescope, many sorts of mounts have been developed over the years, with the majority of effort being put into systems that can track the motion of the stars as the Earth rotates. Fixed-altitude mounts usually have the primary optics fixed at an angle while rotating horizontally. They can cover the sky but only observe objects for the short time when that object passes a specific altitude. Transit mounts are single axis mounts fixed in azimuth while rotating in altitude and this allows the telescope to view the whole sky, but only when the Earths rotation allows the objects to cross through that narrow north-south line. This type of mount is used in Transit telescopes, designed for precision astronomical measurement, Transit mounts are also used to save on cost or where the instruments mass makes movement on more than one axis very difficult, such as large radio telescopes. Altazimuth, altitude-azimuth, or alt-az mounts allow telescopes to be moved in altitude, or azimuth and this meant until recently it was normally used with inexpensive commercial and hobby constructions. Since the invention of digital tracking systems, altazimuth mounts have come to be used in all modern large research telescopes. Digital tracking has also made it a popular telescope mount used in amateur astronomy, besides the mechanical inability to easily follow celestial motion the altazimuth mount does have other limitations. The mount also has blind spot or zenith hole, a spot near the zenith where the rate in the azimuth coordinate becomes too high to accurately follow equatorial motion. These mounts also require a third axis to de-rotate the field as the telescope tracks, alt-alt mounts, or altitude-altitude mounts, are designs similar to horizontal equatorial yoke mounts or Cardan suspension gimbals. This mount is an alternative to the mount that has the advantage of not having a blind spot near the zenith. It has the disadvantage of having all the mass, complexity and these mounts may include a third azimuth axis to rotate the entire mount into an orientation that allows smoother tracking. Slewing or mechanically driving the mounts polar axis in a direction to the Earths rotation allows the telescope to accurately follow the motion of the night sky. Tilting the polar axis adds a level of complexity to the mount, mechanical systems have to be engineered to support one or both ends of this axis. Designs such as German equatorial or cross axis mounts also need large counter weights to counterbalance the mass of the telescope, larger domes and other structures are also needed to cover the increased mechanical size and range of movement of equatorial mounts. Because of this, equatorial mounts become less viable in very large telescopes and have been pretty much replaced by altazimuth mounts for those applications, instead of the classical mounting using two axles, the mirror is supported by six extendable struts. This configuration allows moving the telescope in all six degrees of freedom
2.
Camera
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Thumb|A2016 Nikon D810 A camera is an optical instrument for recording or capturing images, which may be stored locally, transmitted to another location, or both. The images may be individual still photographs or sequences of images constituting videos or movies, the camera is a remote sensing device as it senses subjects without physical contact. The word camera comes from camera obscura, which means dark chamber and is the Latin name of the device for projecting an image of external reality onto a flat surface. The modern photographic camera evolved from the camera obscura, the functioning of the camera is very similar to the functioning of the human eye. A camera may work with the light of the spectrum or with other portions of the electromagnetic spectrum. A still camera is a device which creates a single image of an object or scene. All cameras use the basic design, light enters an enclosed box through a converging lens/convex lens. A shutter mechanism controls the length of time that light can enter the camera, a display, often a liquid crystal display, permits the user to view scene to be recorded and settings such as ISO speed, exposure, and shutter speed. A movie camera or a video camera operates similarly to a camera, except it records a series of static images in rapid succession. When the images are combined and displayed in order, the illusion of motion is achieved, the forerunner to the photographic camera was the camera obscura. The oldest known record of this principle is a description by Han Chinese philosopher Mozi, Mozi correctly asserted that the camera obscura image is inverted because light travels in straight lines from its source. In the 11th century Arab physicist Ibn al-Haytham s wrote very influential essays about experiments with light through an opening in a darkened room. The use of a lens in the opening of a wall or closed window shutter of a room to project images used as a drawing aid has been traced back to circa 1550. Since the late 17th century portable camera obscura devices in tents, before the development of the photographic camera, it had been known for hundreds of years that some substances, such as silver salts, darkened when exposed to sunlight. The first person to use this chemistry to create images was Thomas Wedgwood, to create images, Wedgwood placed items, such as leaves and insect wings, on ceramic pots coated with silver nitrate, and exposed the set-up to light. These images werent permanent, however, as Wedgwood didnt employ a fixing mechanism and he ultimately failed at his goal of using the process to create fixed images created by a camera obscura. The first permanent photograph of an image was made in 1826 by Joseph Nicéphore Niépce using a sliding wooden box camera made by Charles. Niépce had been experimenting with ways to fix the images of a camera obscura since 1816, the photograph Niépce succeeded in creating shows the view from his window
3.
Altazimuth mount
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An altazimuth or alt-azimuth mount is a simple two-axis mount for supporting and rotating an instrument about two perpendicular axes – one vertical and the other horizontal. Rotation about the vertical axis varies the azimuth of the direction of the instrument. Rotation about the horizontal axis varies the altitude of the pointing direction and these mounts are used, for example, with telescopes, cameras, radio antennas, heliostat mirrors, solar panels, and guns and similar weapons. Several names are given to this kind of mount, including altitude-azimuth, azimuth-elevation, a gun turret is essentially an alt-azimuth mount for a gun, and a standard camera tripod is an alt-azimuth mount as well. When used as a telescope mount, the biggest advantage of an alt-azimuth mount is the simplicity of its mechanical design. The primary disadvantage is its inability to follow objects in the night sky as the Earth spins on its axis. On the other hand, an equatorial mount only needs to be rotated about an axis, at a constant rate. Altazimuth mounts need to be rotated about both axes at variable rates, achieved via microprocessor based two-axis drive systems, to track equatorial motion and this imparts an uneven rotation to the field of view that also has to be corrected via a microprocessor based counter rotation system. The design also does not allow for the use of setting circles to locate astronomical objects although modern digital setting circles have removed this shortcoming. Another limitation is the problem of gimbal lock at zenith pointing, when tracking at elevations close to 90°, the azimuth axis must rotate very quickly, if the altitude is exactly 90°, the speed is infinite. Thus, altazimuth telescopes, although they can point in any direction, cannot track smoothly within a zenith blind spot, typical current applications of altazimuth mounts include, Research telescopes Mounts for very large telescopes. In the largest telescopes the mass and cost of a mount is prohibitive. The simple structure of an alt-azimuth mount allows significant cost reductions, an altazimuth mount also reduces the cost in the dome structure covering the telescope since the simplified motion of the telescope means the structure can be more compact. Altazimuth mounts are cheap and simple to use
4.
Astrophotography
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Astrophotography is a specialized type of photography for recording photos of astronomical objects and large areas of the night sky. The first photograph of an object was taken in 1840. This is done by long time exposure since both film and digital cameras can accumulate and sum light photons over long periods of time. Astrophotography is a subdiscipline in amateur astronomy usually seeking aesthetically pleasing images rather than scientific data. Amateurs use a range of special equipment and techniques. With a few exceptions, astronomical photography employs long exposures since both film and digital imaging devices can accumulate and light photons over long periods of time, the amount of light hitting the film or detector is also increased by increasing the diameter of the primary optics being used. Since the Earth is constantly rotating, telescopes and equipment are rotated in the direction to follow the apparent motion of the stars overhead. This is accomplished by using either equatorial or computer-controlled altazimuth telescope mounts to keep celestial objects centered while the earth rotates, all telescope mount systems suffer from induced tracking error due to imperfect motor drives and mechanical sag of the telescope. Tracking errors are corrected by keeping a selected aiming point, usually a bright guide star, sometimes the object to be imaged is moving, so the telescope has to be kept constantly centered on that object. Guiding was formerly done manually throughout the exposure with an observer standing at the telescope making corrections to keep a cross hair on the guide star, since the advent of computer-controlled systems this is accomplished by an automated systems in professional and even amateur equipment. These all require specialized equipment such as telescopes designed for imaging, for wide field of view. Astronomical CCD cameras may use cryogenic cooling to reduce thermal noise, specialized filters are also used to record images in specific wavelengths. The development of astrophotography as a tool was pioneered in the mid-19th century for the most part by experimenters and amateur astronomers. Because of the long exposures needed to capture relatively faint astronomical objects. Early photographic processes also had limitations, the daguerreotype process was far too slow to record anything but the brightest objects, and the wet plate collodion process limited exposures to the time the plate could stay wet. The first-known attempt at astronomical photography was by Louis Jacques Mandé Daguerre, inventor of the process which bears his name. Tracking errors in guiding the telescope during the long exposure meant the photograph came out as an indistinct fuzzy spot, the Sun may have been first photographed in an 1845 daguerreotype by the French physicists Léon Foucault and Hippolyte Fizeau. No photographic alteration was caused by the light of the corona condensed by a lens for two minutes, during totality, on a sheet of paper prepared with bromide of silver, the Suns solar corona was first successfully imaged during the Solar eclipse of July 28,1851
5.
Catadioptric system
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A catadioptric optical system is one where refraction and reflection are combined in an optical system, usually via lenses and curved mirrors. Catadioptric combinations are used in focusing systems such as lights, headlamps, early lighthouse focusing systems, optical telescopes, microscopes. Other optical systems use lenses and mirrors are also referred to as catadioptric such as surveillance catadioptric sensors. Catadioptric combinations have been used in many optical systems. In the 1820s, Augustin-Jean Fresnel developed several catadioptric lighthouse reflectors, léon Foucault developed a catadioptric microscope in 1859 to counteract aberrations of using a lens to image objects at high power. In 1876 a French engineer, A. Mangin, invented what has come to be called the Mangin mirror, the two surfaces of the reflector have different radii to correct the aberration of the spherical mirror. Light passes through the glass twice, making the system act like a triplet lens. Mangin mirrors were used in searchlights, where they produced a true parallel beam. Catadioptric telescopes are optical telescopes that combine specifically shaped mirrors and lenses to form an image and their designs can have simple all-spherical surfaces and can take advantage of a folded optical path that reduces the mass of the telescope, making them easier to manufacture. Catadioptric dialytes are the earliest type of catadioptric telescope and they consist of a single-element refractor objective combined with a silver-backed negative lens. The first of these was the Hamiltonian telescope patented by W. F. Hamilton in 1814, there are several telescope designs that take advantage of placing one or more full-diameter lenses in front of a spherical primary mirror. Some of these designs have been adapted to create compact, long-focal-length catadioptric cassegrains, the Schmidt corrector, the first full-diameter corrector plate, was used in Bernhard Schmidts 1931 Schmidt camera. The relatively thin and lightweight corrector allows Schmidt cameras to be constructed in diameters up to 1.3 m, the design has lent itself to many Schmidt variants. Popular sub-types Schmidt–Cassegrain telescopes are one of the most popular commercial designs on the amateur astronomical market, the design replaces the Schmidt Camera film holder with a Cassegrain secondary mirror, making a folded optical path with a long focal length and a narrow field of view. Wartime secrecy kept these inventors from knowing about each others designs, albert Bouwers built a prototype meniscus telescope in August 1940 and patented it in February 1941. It used a spherically concentric meniscus and was suitable as a monochromatic astronomical camera. In a later design he added a cemented doublet to correct chromatic aberration, Dmitri Maksutov built a prototype for a similar type of meniscus telescope, the Maksutov telescope, in October 1941 and patented it in November of that same year. His design corrected spherical and chromatic aberrations by placing a weak negative-shaped meniscus corrector closer to the primary mirror, popular sub-types Maksutov–Cassegrain telescopes are the most commonly seen design that uses a meniscus corrector, a variant of the Maksutov telescope
6.
Mount Wilson Observatory
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The Mount Wilson Observatory is an astronomical observatory in Los Angeles County, California, United States. The MWO is located on Mount Wilson, a 1, 740-metre peak in the San Gabriel Mountains near Pasadena, the observatory was conceived and founded by George Ellery Hale, who had previously built the 1 meter telescope at the Yerkes Observatory, then the worlds largest telescope. The Mount Wilson Solar Observatory was first funded by the Carnegie Institution of Washington in 1904, among the conditions of the lease was that it allow public access. There are three solar telescopes at Mount Wilson Observatory, today, just one of these telescopes, the 60 foot Solar Tower, is still used for solar research. The Snow Solar Telescope was the first telescope installed at the fledgling Mount Wilson Solar Observatory and it was the worlds first permanently mounted solar telescope. Solar telescopes had previously been portable so they could be taken to solar eclipses around the world, the telescope was donated to Yerkes Observatory by Helen Snow of Chicago. George Ellery Hale, then director of Yerkes, had the telescope brought to Mount Wilson to put it into service as a scientific instrument. Stellar research soon followed as the brightest stars could have their spectra recorded with very long exposures on glass plates, today the Snow solar telescope is mostly used by undergraduate students who get hands on training in solar physics and spectroscopy. It was also used publicly for the May 9,2016 transit of Mercury across the face of the sun, the 60-foot Solar Tower soon built on the work started at the Snow telescope. At its completion in 1908, the tower design of the 60 foot focal length solar telescope allowed much higher resolution of the solar image. The higher resolution came from situating the optics higher above the ground, on June 25,1908, Hale would record Zeeman splitting in the spectrum of a sunspot, showing for the first time that magnetic fields existed somewhere besides the earth. A later discovery was of the polarity in sunspots of the new solar cycle of 1912. The success of the 60 foot Tower prompted Hale to pursue yet another, taller tower telescope, in the 1960s, Robert Leighton discovered the sun had a 5-minute oscillation and the field of heliosiesmology was born. The 60 foot Tower is operated by the Department of Physics, the 150-foot focal length solar tower expanded on the solar tower design with its tower-in-a-tower design. An inner tower supports the optics above, while an outer tower and this design allowed complete isolation of the optics from the effect of wind swaying the tower. Two mirrors feed sunlight to a 12-inch lens which focuses light down at the ground floor and it was first completed in 1910, but unsatisfactory optics caused a two-year delay before a suitable doublet lens was installed. Research included solar rotation, sunspot polarities, daily sunspot drawings, the solar telescope would be the worlds largest for 50 years until the McMath-Pierce Solar telescope was completed at Kitt Peak in Arizona in 1962. In 1985, UCLA took over operation of the tower from the Carnegie Observatories after it was decided to stop funding the observatory
7.
Hale Telescope
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The Hale Telescope is a 200-inch, f/3.3 reflecting telescope at the Palomar Observatory in California, US, named after astronomer George Ellery Hale. With funding from the Rockefeller Foundation, he orchestrated the planning, design, and construction of the observatory and it is still in active use. It was the largest optical telescope in the world from its completion in 1948 until the BTA-6 was built in 1976, the chief optical designer for Hales previous 100-inch telescope was George Willis Ritchey, who intended the new telescope to be of Ritchey–Chrétien design. Compared to the parabolic primary, this design would have provided sharper images over a larger usable field of view. However, Ritchey and Hale had a falling out, with the project already late and over budget, Hale refused to adopt the new design, with its complex curvatures, and Ritchey left the project. The Mount Palomar Hale telescope turned out to be the last world-leading telescope to have a primary mirror. The Corning Glass Works was assigned the task of making a 200-inch primary mirror, construction of the observatory facilities and dome started in 1936, but because of interruptions caused by World War II, the telescope was not completed until 1948 when it was dedicated. Due to slight distortions of images, corrections were made to the telescope throughout 1949 and it became available for research in 1950. The 200-inch Hale saw first light on January 26,1949 under the direction of American astronomer Edwin Powell Hubble, targeting NGC2261, the photographs made then were published in the astronomical literature and in the May 7,1949 issue of Colliers Magazine. It is equipped with optical and infrared array imagers, spectrographs. It has also used lucky cam imaging, which in combination with adaptive optics pushed the mirror close to its resolution for certain types of viewing. One of the Corning Labs glass test blanks for the Hale was used for the C. Donald Shane telescopes 120-inch primary mirror, the collecting area of the Hale is about 31,000 square inches. The optical tube assembly uses a Serrurier truss, then newly invented by Mark U, Serrurier of Caltech in Pasadena in 1935, designed to flex in such a way as to keep all of the optics in alignment. Theodore von Karman designed the system to avoid potential issues with turbulence during tracking. Pyrex was chosen for its low expansion qualities so the mirror would not distort the images produced when it changed shape due to temperature variations. The mirror was cast in a mold with 36 raised mold blocks, the shape of a central hole was also part of the mold so light could pass through the finished mirror when it was used in a Cassegrain configuration. The defective mirror was used to test the annealing process, after the mold was re-engineered, a second mirror was successfully cast. After cooling several months, the mirror blank was transported by rail to Pasadena
8.
Dobsonian telescope
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Dobsons telescopes featured a simplified mechanical design that was easy to manufacture from readily available components to create a large, portable, low-cost telescope. The design is optimized for visually observing faint, deep-sky objects such as nebulae and this type of observation requires a large objective diameter of relatively short focal length and portability for travel to relatively less light-polluted locations. Dobsonians are popular in the telescope making community, where the design was pioneered. A number of commercial telescope makers also sell telescopes based on this design and it is hard to classify the Dobsonian Telescope as a single invention. In the field of amateur telescope making most, if not all, john Dobson, credited as having invented this design in the 1950s, points out that for hundreds of years, wars were fought using cannon on Dobsonian mounts. Since he built these telescopes as aids in his avocation of instructional sidewalk astronomy, Dobsons design allows a builder with minimal skill to make an extremely large telescope out of common items. Dobson optimized the design for visual observation of faint objects such as clusters, nebulae. These dim objects require a large objective mirror able to gather a large amount of light, because deep sky observing often requires travel to dark locations away from city lights, the design benefits from being more compact, portable, and rugged than standard large Newtonian telescopes. Construction tubes, Dobson replaced the traditional aluminum or fiberglass telescope tube with the thick compressed paper tubes used in construction to concrete columns. Sonotubes, the leading brand employed by Dobson, are less expensive than commercially available telescope tubes and are available in large sizes. Dobsonian scopes are intended to be transported out to dark sky locations, Sonotubes have the added advantage of being thermally stable and non-conductive which minimizes unwanted convection currents in the light path caused by handling of the tube assembly. A square mirrorbox, Dobson used a box for the tube base. This gave a rigid surface to attach the carpet support for the porthole mirrors he was using. A simple alt-azimuth mount, Dobson opted for a simple to build and he used a “gun carriage type” design consisting of a flat platform on which sits a rotating box with semicircular depressions cut in the top for the altitude bearings. All parts were made from plywood and other common materials, for the azimuth motion Dobson used a combination of Teflon blocks turning on a flat Formica covered surface. For the altitude motion, Dobson used a large diameter axle closet flange turning on Teflon bearing blocks attached to the altitude cutouts. The design of Dobsonian telescopes has evolved over the years, but most commercial or amateur-built Dobsonian telescopes follow many or most of the design concepts, the Dobsonian design has the following characteristics, Altazimuth mount, An equatorial telescope mount with clock drive was left out of the design. Equatorial mounts tend to be massive, expensive, complicated, and have the characteristics of putting the eyepiece of Newtonian telescopes in very hard to access positions
9.
Earth's rotation
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Earths rotation is the rotation of the planet Earth around its own axis. The Earth rotates from the west towards east, as viewed from North Star or polestar Polaris, the Earth turns counter-clockwise. The North Pole, also known as the Geographic North Pole or Terrestrial North Pole, is the point in the Northern Hemisphere where the Earths axis of rotation meets its surface and this point is distinct from the Earths North Magnetic Pole. The South Pole is the point where the Earths axis of rotation intersects its surface. The Earth rotates once in about 24 hours with respect to the sun, Earths rotation is slowing slightly with time, thus, a day was shorter in the past. This is due to the effects the Moon has on Earths rotation. Atomic clocks show that a modern-day is longer by about 1.7 milliseconds than a century ago, analysis of historical astronomical records shows a slowing trend of 2.3 milliseconds per century since the 8th century BCE. Among the ancient Greeks, several of the Pythagorean school believed in the rotation of the rather than the apparent diurnal rotation of the heavens. Perhaps the first was Philolaus, though his system was complicated, in the third century BCE, Aristarchus of Samos suggested the suns central place. However, Aristotle in the fourth century criticized the ideas of Philolaus as being based on rather than observation. He established the idea of a sphere of fixed stars that rotated about the earth and this was accepted by most of those who came after, in particular Claudius Ptolemy, who thought the earth would be devastated by gales if it rotated. In the 10th century, some Muslim astronomers accepted that the Earth rotates around its axis, treatises were written to discuss its possibility, either as refutations or expressing doubts about Ptolemys arguments against it. At the Maragha and Samarkand observatories, the Earths rotation was discussed by Tusi and Qushji, in medieval Europe, Thomas Aquinas accepted Aristotles view and so, reluctantly, did John Buridan and Nicole Oresme in the fourteenth century. Not until Nicolaus Copernicus in 1543 adopted a heliocentric world system did the earths rotation begin to be established, Copernicus pointed out that if the movement of the earth is violent, then the movement of the stars must be very much more so. He acknowledged the contribution of the Pythagoreans and pointed to examples of relative motion, for Copernicus this was the first step in establishing the simpler pattern of planets circling a central sun. Tycho Brahe, who produced accurate observations on which Kepler based his laws, in 1600, William Gilbert strongly supported the earths rotation in his treatise on the earths magnetism and thereby influenced many of his contemporaries. Those like Gilbert who did not openly support or reject the motion of the earth about the sun are often called semi-Copernicans, however, the contributions of Kepler, Galileo and Newton gathered support for the theory of the rotation of the Earth. The earths rotation implies that the bulges and the poles are flattened
10.
Amateur astronomy
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Amateur astronomy is a hobby whose participants enjoy watching the sky, and the abundance of objects found in it with the unaided eye, binoculars, or telescopes. Many amateurs are beginners or hobbyists, while others have a degree of experience in astronomy and often assist. Amateur astronomers often look at the sky using nothing more than their eyes, people have studied the sky throughout history in an amateur framework, without any formal method of funding. It is only within about the past century, however, that amateur astronomy has become an activity clearly distinguished from professional astronomy, collectively, amateur astronomers observe a variety of celestial objects and phenomena. Common targets of amateur astronomers include the Moon, planets, stars, comets, meteor showers, and a variety of deep sky objects such as clusters, galaxies. Many amateurs like to specialise in observing particular objects, types of objects, one branch of amateur astronomy, amateur astrophotography, involves the taking of photos of the night sky. Most amateur astronomers work at visible wavelengths, but a small minority experiment with wavelengths outside the visible spectrum, non-visual amateur astronomy includes the use of infrared filters on conventional telescopes, and also the use of radio telescopes. Some amateur astronomers use home-made radio telescopes, while others use radio telescopes that were built for astronomy research but have since been made available for use by amateurs. The One-Mile Telescope is one such example, Amateur astronomers use a range of instruments to study the sky, depending on a combination of their interests and resources. Commercial telescopes are available, new and used, but it is common for amateur astronomers to build their own custom telescopes. Some people even focus on amateur telescope making as their primary interest within the hobby of amateur astronomy, although specialized and experienced amateur astronomers tend to acquire more specialized and more powerful equipment over time, relatively simple equipment is often preferred for certain tasks. Amateur astronomers also use star charts that, depending on experience and intentions, Amateur astronomers often like to keep records of their observations, which usually takes the form of an observing log. Observing logs typically record details about which objects were observed and when, sketching is sometimes used within logs, and photographic records of observations have also been used in recent times. The information gathered is used to help studies and interactions between amateur astronomers in yearly gatherings, although not professional information or credible, it is a way for the hobby lovers to share their new sightings and experiences. The Internet is a tool of amateur astronomers. The popularity of CCD imaging among amateurs has led to large numbers of web sites being written by individuals about their images, much of the social interaction of amateur astronomy occurs on mailing lists or discussion groups. Discussion group servers host numerous astronomy lists, a great deal of the commerce of amateur astronomy, the buying and selling of equipment, occurs online. Many amateurs use online tools to plan their observing sessions using tools such as the Clear Sky Chart
