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Clock Drive
In astronomy, a clock drive (also known as a field rotator) is a motor-controlled mechanism used to move an equatorial mounted telescope along one axis to keep the aim in exact sync with the apparent motion of the fixed stars on the celestial sphere. Overview Clock drives work by rotating a telescope mount's polar axis, the axis parallel to the Earth's polar axis (also called the right ascension axis) in the opposite direction to the Earth's rotation one revolution every 23 hours and 56 minutes (called ''sidereal day''), thereby canceling that motion. This allows the telescope to stay fixed on a certain point in the sky without having to be constantly re-aimed due to the Earth's rotation. The mechanism itself used to be clockwork but nowadays is usually electrically driven. Clock drives can be light and portable for smaller telescopes or can be exceedingly heavy and complex for larger ones such as the 60-inch telescope at the Mount Wilson Observatory. Clock-driven equatorial pla ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Aldershot Observatory 02
Aldershot () is a town in Hampshire, England. It lies on heathland in the extreme northeast corner of the county, southwest of London. The area is administered by Rushmoor Borough Council. The town has a population of 37,131, while the Farnborough/Aldershot built-up area, Aldershot Urban Area, a loose conurbation (which also includes other towns such as Camberley, Farnborough, Hampshire, Farnborough, and Farnham) has a population of 243,344, making it the thirtieth-largest urban area in the UK. Aldershot is known as the "Home of the British Army", a connection which led to its rapid growth from a small village to a Victorian era, Victorian town. History Early history The name may have derived from alder trees found in the area (from the Old English 'alder-holt' meaning copse of alder trees). Any settlement, though not mentioned by name, would have been included as part of the Hundred (division), Hundred of Crondall referred to in the Domesday Book of 1086. The Church of St M ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Song Dynasty
The Song dynasty (; ; 960–1279) was an imperial dynasty of China that began in 960 and lasted until 1279. The dynasty was founded by Emperor Taizu of Song following his usurpation of the throne of the Later Zhou. The Song conquered the rest of the Ten Kingdoms, ending the Five Dynasties and Ten Kingdoms period. The Song often came into conflict with the contemporaneous Liao, Western Xia and Jin dynasties in northern China. After retreating to southern China, the Song was eventually conquered by the Mongol-led Yuan dynasty. The dynasty is divided into two periods: Northern Song and Southern Song. During the Northern Song (; 960–1127), the capital was in the northern city of Bianjing (now Kaifeng) and the dynasty controlled most of what is now Eastern China. The Southern Song (; 1127–1279) refers to the period after the Song lost control of its northern half to the Jurchen-led Jin dynasty in the Jin–Song Wars. At that time, the Song court retreated south of the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Equatorial Mount
An equatorial mount is a mount for instruments that compensates for Earth's rotation by having one rotational axis, the polar axis, parallel to the Earth's axis of rotation. This type of mount is used for astronomical telescopes and cameras. The advantage of an equatorial mount lies in its ability to allow the instrument attached to it to stay fixed on any celestial object with diurnal motion by driving one axis at a constant speed. Such an arrangement is called a sidereal or clock drive. Equatorial mounts achieve this by aligning their rotational axis with the Earth, a process known as polar alignment. Astronomical telescope mounts In astronomical telescope mounts, the equatorial axis (the '' right ascension'') is paired with a second perpendicular axis of motion (known as the '' declination''). The equatorial axis of the mount is often equipped with a motorized "''clock drive''", that rotates that axis one revolution every 23 hours and 56 minutes in exact sync with the appar ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Achromatic Lens
An achromatic lens or achromat is a lens that is designed to limit the effects of chromatic and spherical aberration. Achromatic lenses are corrected to bring two wavelengths (typically red and blue) into focus on the same plane. The most common type of achromat is the achromatic doublet, which is composed of two individual lenses made from glasses with different amounts of dispersion. Typically, one element is a negative (concave) element made out of flint glass such as F2, which has relatively high dispersion, and the other is a positive (convex) element made of crown glass such as BK7, which has lower dispersion. The lens elements are mounted next to each other, often cemented together, and shaped so that the chromatic aberration of one is counterbalanced by that of the other. In the most common type (shown), the positive power of the crown lens element is not quite equalled by the negative power of the flint lens element. Together they form a weak positive lens that will b ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tartu Observatory
The Tartu Observatory ( et, Tartu Observatoorium) is the largest astronomical observatory in Estonia. On 1 January 2018, Tartu Observatory was joined again to the University of Tartu, and the observatory is now an institute of the university. It is located on the Tõravere hill, about 20 km south-west of Tartu in Nõo Parish, Tartu County. The old Tartu Observatory located in Tartu city centre, is known internationally for its connection to Friedrich Georg Wilhelm von Struve and the Struve Geodetic Arc, of which it is the first reference point. History The Tartu Observatory was founded at the Imperial University of Dorpat as it was reopened in 1802. The observatory building was completed in 1810 on the Toome hill in Dorpat. The instruments were installed in 1814 by von Struve who subsequently started observations. In 1824, a 9" Fraunhofer refractor arrived, the largest achromatic telescope in the world at the time. When von Struve began assembling his Geodetic Arc in ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Joseph Von Fraunhofer
Joseph Ritter von Fraunhofer (; ; 6 March 1787 – 7 June 1826) was a German physicist and optical lens manufacturer. He made optical glass, an achromatic telescope, and objective lenses. He also invented the spectroscope and developed diffraction grating. In 1814, he discovered and studied the dark absorption lines in the spectrum of the sun now known as Fraunhofer lines. The German research organization Fraunhofer Society, which is Europe's biggest Society for the advancement of applied research, is named after him. Biography Joseph Fraunhofer was the 11th child, born into a Roman Catholic family in Straubing, in the Electorate of Bavaria, to Franz Xaver Fraunhofer and Maria Anna Fröhlich. He was orphaned at the age of 11 and started working as an apprentice to a harsh glassmaker named Philipp Anton Weichelsberger. In 1801, the workshop in which he was working collapsed, and he was buried in the rubble. The rescue operation was led by Prince-Elector Maximilian Joseph. The ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Henry Lonsdale
Henry Lonsdale M.D. (1816–1876) was an English physician, now known as a biographer. Early life Born in Carlisle, Cumberland, he was son of Henry Lonsdale, a tradesman there. After attending a local school he was apprenticed in 1831 to Messrs. Anderson & Hodgson, medical practitioners in Carlisle. In 1834 he went to study medicine at Edinburgh, and was in his third year appointed assistant to Robert Knox the anatomist, and also to John Reid, the physiologist. He studied during the summer of 1838 in Paris, and in passing through London became a member of the Royal College of Surgeons and licentiate of the Society of Apothecaries. Physician On his return to Edinburgh Lonsdale graduated M.D. In autumn 1838, overworked, he took temporary charge of a country practice at Raughton Head in Cumberland. He helped to found the Inglewood Agricultural Society, a monthly club, the first of its kind in the county. He also gave a course of popular lectures on science, and acquired the fr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
George Graham (clockmaker)
George Graham, FRS (7 July 1673, maybe 1675 – 16 November 1751) was an English clockmaker, inventor, and geophysicist, and a Fellow of the Royal Society. He was born in Kirklinton, Cumberland. A Friend (Quaker) like his mentor Thomas Tompion, Graham left Cumberland in 1688 for London to work with Tompion. He later married Tompion's niece, Elizabeth Tompion. Career Graham was partner to the influential English clockmaker Thomas Tompion during the last few years of Tompion's life. Graham is credited with inventing several design improvements to the pendulum clock, inventing the mercury pendulum and also the orrery. He was made Master of the Worshipful Company of Clockmakers in 1722. Between 1730 and 1738, Graham had as an apprentice Thomas Mudge, who went on to be an eminent watchmaker in his own right, and invented the lever escapement, an important development for pocket watches.Harold Bagust, "The Greater Genius?", 2006, Ian Allan Publishing, (page 15) He was widely ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Setting Circles
Setting circles are used on telescopes equipped with an equatorial mount to find astronomical objects in the sky by their equatorial coordinates often used in star charts or ephemerides. Description Setting circles consist of two graduated disks attached to the axes – right ascension (RA) and declination (DEC) – of an equatorial mount. The RA disk is graduated into hours, minutes, and seconds. The DEC disk is graduated into degrees, arcminutes, and arcseconds. Since the RA coordinates are fixed onto the celestial sphere, the RA disk is usually driven by a clock mechanism in sync with sidereal time. Locating an object on the celestial sphere using setting circles is similar to finding a location on a terrestrial map using latitude and longitude. Sometimes the RA setting circle has two scales on it: one for the Northern Hemisphere and one for the Southern. Application Research telescopes Historically setting circles have rivaled the telescopes optics as far as difficulty in ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Giovanni Domenico Cassini
Giovanni Domenico Cassini, also known as Jean-Dominique Cassini (8 June 1625 – 14 September 1712) was an Italian (naturalised French) mathematician, astronomer and engineer. Cassini was born in Perinaldo, near Imperia, at that time in the County of Nice, part of the Savoyard state. Cassini is known for his work on astronomy and engineering. He discovered four satellites of the planet Saturn and noted the division of the rings of Saturn; the Cassini Division was named after him. Giovanni Domenico Cassini was also the first of his family to begin work on the project of creating a topographic map of France. The ''Cassini'' space probe, launched in 1997, was named after him and became the fourth to visit the planet Saturn and the first to orbit the planet. Life Time in Italy Cassini was the son of Jacopo Cassini, a Tuscan, and Giulia Crovesi. In 1648 Cassini accepted a position at the observatory at Panzano, near Bologna, to work with Marquis Cornelio Malvasia, a rich amate ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Aerial Telescope
An aerial telescope is a type of very long focal length refracting telescope, built in the second half of the 17th century, that did not use a tube. Instead, the objective was mounted on a pole, tree, tower, building or other structure on a swivel ball-joint. The observer stood on the ground and held the eyepiece, which was connected to the objective by a string or connecting rod. By holding the string tight and maneuvering the eyepiece, the observer could aim the telescope at objects in the sky. The idea for this type of telescope may have originated in the late 17th century with the Dutch mathematician, astronomer and physicist Christiaan Huygens and his brother Constantijn Huygens, Jr., though it is not clear if they actually invented it. Invention and application Very long "tubed" telescopes Telescopes built in the 17th and early 18th century used single element non-achromatic objective lenses that suffered from interfering rainbow halos (chromatic aberration) introduced b ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Robert Hooke
Robert Hooke FRS (; 18 July 16353 March 1703) was an English polymath active as a scientist, natural philosopher and architect, who is credited to be one of two scientists to discover microorganisms in 1665 using a compound microscope that he built himself, the other scientist being Antoni van Leeuwenhoek in 1676. An impoverished scientific inquirer in young adulthood, he found wealth and esteem by performing over half of the architectural surveys after London's great fire of 1666. Hooke was also a member of the Royal Society and since 1662 was its curator of experiments. Hooke was also Professor of Geometry at Gresham College. As an assistant to physical scientist Robert Boyle, Hooke built the vacuum pumps used in Boyle's experiments on gas law, and himself conducted experiments. In 1673, Hooke built the earliest Gregorian telescope, and then he observed the rotations of the planets Mars and Jupiter. Hooke's 1665 book ''Micrographia'', in which he coined the term "cell", ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
