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Roger Ceragioli - One of the best experts on this subject based on the ideXlab platform.
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William Herschel and the “Front-View” Telescopes
The Scientific Legacy of William Herschel, 2018Co-Authors: Roger CeragioliAbstract:William Herschel is rightly regarded as one of the greatest Telescope makers in history. His instruments vastly exceeded in aperture and light-gathering power all those that came before his time, and established the Reflecting Telescope as a formidable instrument of astronomical research. To understand his research successes – and the limits of his success – we must understand the performance of his Telescopes.The present chapter attempts a comprehensive evaluation of the optical performance of Herschel’s Telescopes. This is possible because of the vast documentation he left behind relating to his building and usage of Telescopes, and also because a substantial number of his surviving mirrors have been tested using modern methods. After an introduction the chapter proceeds with a review of how the Reflecting Telescope developed before Herschel, and a consideration of engineering and materials problems in building reflectors. It then turns to optical matters, considering the types of imaging errors (aberrations) found particularly in Newtonian Telescopes, the design form favored by Herschel. Further on the chapter considers how the theory of those errors (aberration theory) developed before Herschel and into the nineteenth century. Study of the forms of aberration and the history of aberration theory is necessary for understanding what optical errors Herschel saw in his Telescopes, and what he could know – or not know – about them.Following this we consider Herschel’s methods of fabrication and optical testing, in particular concentrating on the small elliptical flat mirrors (“secondaries” or “diagonals”) that are a critical part of any Newtonian Telescope, even today. These petite mirrors form a relatively neglected area of study compared to Herschel’s more physically imposing primary mirrors, which have often been tested optically. It is ironic, therefore, that these small mirrors, precisely because they are used at a 45° tilt, called “oblique incidence” – versus the primaries used at “normal incidence” – have the potential to affect the final telescopic image just as gravely as the primaries, unless they are rigorously flat. Yet before the late nineteenth century there was no accurate method of assessing the surface profile of flat mirrors. The question, therfore, arises: How could Herschel make optically usable diagonal mirrors for Newtonian Telescopes? The analysis and solution of this question forms one of the most important results of the present chapter. The upshot is that because Herschel (and other eighteenth-century Telescope makers) could not make accurate flat mirrors – or any usable diagonal mirrors of large dimension – Herschel turned to the so-called “front-view,” or “Herschelian,” Telescope for his largest instruments.With all this as background, the next sections present a detailed discussion of the performance of eighteenth and early nineteenth-century Newtonian Telescopes, and a similar consideration of “front-views.” Attention is also devoted throughout the chapter to explaining how Lord Rosse’s giant Newtonian Telescopes of the mid-nineteenth century consituted a dramatic improvement on what came before and paved the way for the final triumph of the Reflecting Telescope over the refracting in astronomical research at the beginning of the twentieth century.The final section of the chapter discusses the protracted cover-up and controversy surrounding the failure of Herschel’s most famous Telescope, his so-called 40-ft front-view – by far the most massive Telescope constructed before the mid-nineteenth century – containing a 48-in. diameter mirror. The cover-up of this monumentally expensive failure ultimately ricocheted onto William Herschel’s son, John, who became embroiled in an acrimonious exchange of letters in the 1840s with Thomas Romney Robinson, director of the Armagh Observatory and ardent admirer of Lord Rosse’s grand achievements. Robinson emerged from the exchange victorious, but John, the dutiful son, although scathed, appeared the nobler figure. The tragic clash between these great men closes out the chapter.
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William Herschel and the “Front-View” Telescopes
Historical & Cultural Astronomy, 2017Co-Authors: Roger CeragioliAbstract:William Herschel is rightly regarded as one of the greatest Telescope makers in history. His instruments vastly exceeded in aperture and light-gathering power all those that came before his time, and established the Reflecting Telescope as a formidable instrument of astronomical research. To understand his research successes – and the limits of his success – we must understand the performance of his Telescopes.
Raymond N. Wilson - One of the best experts on this subject based on the ideXlab platform.
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Modern Telescope developments: pupil segmentation and techniques to reduce mass
Astronomy and Astrophysics Library, 1999Co-Authors: Raymond N. WilsonAbstract:In Chap. 5 of RTO I an account was given of the evolution of the Reflecting Telescope from the optical point of view from Lord Rosse, about 1830, up to about 1980. From about this time, the evolution of Telescope optics, which had retained certain essential features ever since Galileo’s Telescopes in 1610, was supplanted by a revolution. A summary of this process was recently given by the author [3.1].
A. D. C. Simpson - One of the best experts on this subject based on the ideXlab platform.
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AN ACCOUNT OF THE ROYAL SOCIETY'S NEWTON Telescope*
Notes and Records of the Royal Society of London, 1996Co-Authors: F. B. A. A. Rupert Hall, A. D. C. SimpsonAbstract:9THE FIRST Reflecting Telescope INUENTED BI S R ISAAC NEWTON AND MADE WITH HIS OWN HANDS IN THE YEAR 1671’ These words are engraved on a brass plate screwed to the base of the little Telescope that has been revered by the Royal Society as the handiwork of its greatest Fellow, Isaac Newton (1642-1727), who was President of the Society from 1703 until his death. Newton is normally credited with the invention of the Reflecting Telescope, an invention widely and enthusiastically publicized by the Royal Society when Newton sent one of his instruments to London to be inspected by the Society’s Council in 1671. In spite of the confident message on this engraved plate (its eccentric orthography suggesting an enhanced antiquity), the original Telescope presented by Newton in 1671 did not remain in the Society’s care. The surviving Newton Telescope (figure 1) was presented to the Society in 1766 by the antiquary George Scott, F.R.S., on behalf of Heath & Wing, a firm of scientific instrument-makers in the Strand, London. Scott affirmed that it was ‘formerly belonging to Sir Isaac Newton, P.R.S., and made by himself’. But can this instrument properly be associated with Newton? This brief account looks at the history and provenance of Newton’s early Reflecting Telescopes and argues that at least part of the extant instrument may be Newton’s, making it possibly the world’s oldest surviving Reflecting Telescope.
Gerhard Neukum - One of the best experts on this subject based on the ideXlab platform.
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Cassini Imaging Science: Instrument Characteristics And Anticipated Scientific Investigations At Saturn
Space Science Reviews, 2004Co-Authors: Carolyn C. Porco, Robert A. West, Steven Squyres, Alfred Mcewen, Anthony Delgenio, Andrew P. Ingersoll, Torrence V. Johnson, Carl D. Murray, Peter Thomas, Gerhard NeukumAbstract:The Cassini Imaging Science Subsystem (ISS) is the highest-resolution two-dimensional imaging device on the Cassini Orbiter and has been designed for investigations of the bodies and phenomena found within the Saturnian planetary system. It consists of two framing cameras: a narrow angle, Reflecting Telescope with a 2-m focal length and a square field of view (FOV) 0.35^∘ across, and a wide-angle refractor with a 0.2-m focal length and a FOV 3.5^∘ across. At the heart of each camera is a charged coupled device (CCD) detector consisting of a 1024 square array of pixels, each 12 μ on a side. The data system allows many options for data collection, including choices for on-chip summing, rapid imaging and data compression. Each camera is outfitted with a large number of spectral filters which, taken together, span the electromagnetic spectrum from 200 to 1100 nm. These were chosen to address a multitude of Saturn-system scientific objectives: sounding the three-dimensional cloud structure and meteorology of the Saturn and Titan atmospheres, capturing lightning on both bodies, imaging the surfaces of Saturn’s many icy satellites, determining the structure of its enormous ring system, searching for previously undiscovered Saturnian moons (within and exterior to the rings), peering through the hazy Titan atmosphere to its yet-unexplored surface, and in general searching for temporal variability throughout the system on a variety of time scales. The ISS is also the optical navigation instrument for the Cassini mission. We describe here the capabilities and characteristics of the Cassini ISS, determined from both ground calibration data and in-flight data taken during cruise, and the Saturn-system investigations that will be conducted with it. At the time of writing, Cassini is approaching Saturn and the images returned to Earth thus far are both breathtaking and promising.
Wang Gang - One of the best experts on this subject based on the ideXlab platform.
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Point-Ahead Angle and Coalignment Error Measurement Method for Free-Space Optical Communication Systems
JOURNAL OF LIGHTWAVE TECHNOLOGY, 2017Co-Authors: Wang Jianmin, Ye Zhou, Bai Rumeng, Wang GangAbstract:Microradian tracking and pointing errors significantly affect the link performance and the bit error probability in free-space optical communication. This paper proposes the measurement method for point-ahead angle and coalignment error, which can significantly mitigate the tracking and pointing error, thus reduces the power of the free-space optical communication system. By using technologies of corner cube reflector, off-axis Reflecting Telescope, vacuum long-light path and anti-interference support structure design, microangles can be measured accurately, especially the coalignment error angle which is formed by two wide, incoherent beams nearly antiparallel to each other. This paper introduces the measuring equipment's structure, together with the measurement method and theoretical measurement model. The measuring accuracy analysis indicated that the measurement uncertainty of both point-ahead angle and coalignment error was superior to 0.2 mu rad and the validation experimental results proved that measuring accuracies of point-ahead angle and coalignment error are all smaller than 1 mu rad.Ministry of Industry and Information Technology; National Defense Technology Basic Research Project [J312012A001]SCI(E)ARTICLE183886-38933