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Digges, Leonard - TELESCOPES

lens astronomy thomas radio

It is not clear who made the first telescope. It may well have been , who probably made a telescope about 1550, with a convex lens whose image was reflected to the side by a concave mirror for viewing. A claim has long been made for Hans Lippershay ( c .1570– c .1619), a Dutch spectacle maker who sought a patent in 1608 for a design we would now class as Galilean. What is certain is that such telescopes were on sale in Paris, Milan and London in 1609 and that quickly heard of the device, deduced its construction , made several for himself and within a year had seen mountains on the Moon, sunspots, the phases of Venus and the four larger satellites of Jupiter, all for the first time. His best telescope had a magnification of about 30 ×. In the next century many more refracting telescopes (ie using lenses only) were made. In design, a positive lens forms the eyepiece; the image is inverted, but for terrestrial use a second lens in the eyepiece gives an erect image. These early telescopes were awkward to use; in particular, as the red and blue ends of the spectrum are not brought to the same focus by a simple lens, the image is seen to have colour fringes.

Became interested in telescopes in the 1660s, but soon decided (incorrectly) that colour fringes were unavoidable with lenses, and in 1668, when he was 26, he made for himself a small reflecting telescope which solved this problem .

The value of a telescope in astronomy depends largely on the area of its main lens or mirror, which gathers light and so allows the eye (or a camera) to observe small, dim, or distant objects by concentrating their light. cast, ground and polished mirrors for his telescopes (which were of Newtonian or related type) up to 48 in (122 cm) across, with a focal length of up to 40 ft (12 m), and used them to discover a new planet (Uranus), to examine nebulae (clouds of luminous gas or dust) and to show that the Milky Way is dense with stars. The mirrors were made of an alloy of copper and tin, and soon tarnished. In the 1840s the Earl of Rosse made similar mirrors 72 in (183 cm) across, but the unsuitable climate of Birr Castle and Parsonstown, his estate in Eire, gave few clear nights to use his massive instruments.

Refracting telescopes were restored to favour after began making achromatic lenses made of two components: one of crown glass and one of flint glass, a combination that largely solved the colour problem. However, a large lens requires two good surfaces and fairly flawless glass between them, and the largest in use is a 40 in (1 m), with focal length 62 ft (19 m), in the USA.

  In this century reflectors have proved dominant: usually of Pyrex glass, silvered or aluminized, driven electrically to follow the apparent motion of the stars, and linked to a spectroscope, a camera or an electronic detector (a CCD, charge-coupled device) rather than a human eye. Their massive mountings provide a substantial engineering problem: in the first half of the 20th-c high locations in California were favoured, and 60 in (1.5 m), 100 in (2.5 m) and 200 in (5 m) instruments are used in the Mount Wilson and Mount Palomar Observatories there. But atmospheric pollution and light pollution from cities have proved a problem, and recent large instruments have been placed at high points in Hawaii, Las Palmas and Chile to reduce this. One of the largest (but of inferior optical quality) is the 6 m (236 in) reflector installed in 1969 on Mt Pastukhov in the northern Caucasus.

Telescopes can also be designed to detect radiation outside the visible range, and the radio, ultraviolet, infrared and X-ray regions are all much studied. The Second World War gave a great impetus to astronomy, wartime radar and rocket missiles giving a basis for major advances. Radio astronomy stemmed from work by , who showed that the stars included radio sources, studied after the war by and others. An infrared astronomical satellite (IRAS) was launched in 1983, with a 24 in (61 cm) reflecting telescope for infrared rays; it survived for 10 months and located many infrared sources. Telescopes for use in the ultraviolet spectrum had been used in satellites in the 1970s. By 1986 the space probe Giotto passed close to comet and transmitted TV pictures of its nucleus to Earth (see chronology); in 1990 satellites were launched carrying a telescope to detect X-ray sources among stellar objects (ROSAT), and a 95 in (2.4 m) reflecting telescope (named after ) to observe deep space. The Hubble Space Telescope, after repairs in space had corrected some defects, proved to be excellent, and entirely free from unwanted effects due to the Earth’s atmosphere; the data are transmitted by radio. The period 1950–2050 should be a golden age for astronomy, with new information becoming available at an unprecedented rate. At last, after 380 years, astronomers have escaped from the great restriction on their observational work, the Earth’s atmosphere.

At the time of writing, the world’s largest optical telescope is the Keck I, on the summit of Mauna Kea (4200 m/13 780 ft), Hawaii. It weighs 297 t, and the mirror system is 10 m in diameter and consists of 36 hexagonal segments fitted together. Its huge size and good location enable it to record very distant and faint objects, allowing better estimates to be made of the size and age of the universe than any made previously. With its nearby sibling Keck II complete, the paired system, used as an optical interferometer, gives high resolution: and the key role of optical astronomy will be reaffirmed and Thomas Digges ( c .1546–1595) English mathematicians, surveyors and probable inventors of the telescope.

Following his studies at Oxford, Leonard Digges published his book Prognostication which sold well in various editions from 1553. It contained astronomical, astrological and meteorological tables and advice, and was followed in 1556 by a book on practical surveying. However, in early 1554 he took part, with others from his county of Kent, in a nationwide revolt against a Catholic royal marriage. The revolt was easily suppressed and its leaders beheaded; Digges was also condemned but later reprieved.

When he died aged 39, he left his 13-year old son Thomas in the care of the mathematician John Dee (1527–1608) and the boy grew up with the same interests as his father. In 1571, when he was 25, Thomas published Pantometria , a book on surveying originally drafted by his father and ‘lately finished’ by Thomas himself. It contains a description of a telescope using a lens and a mirror; this is amplified in a report prepared for Elizabeth I’s government in 1585, which credits the device to Leonard Digges and his son and which clearly has in mind its military uses. It is likely that Thomas Digges used it to observe the sky and was impressed by the great number of stars it made visible.

However, the effective beginning of observational astronomy came with work in 1610, when he used a refracting telescope made by himself and first saw mountains on the moon, the phases of Venus, Jupiter’s satellites and sunspots. Improved designs of reflecting telescopes due to set these reflectors on the path of dominance for astronomical use which they later achieved (see panel ‘Telescopes’).

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about 5 years ago

This is an interesting article, but there are no less than THREE places where you have not included the names of the people you are talking about, which largely destroys the whole point of the article.

a) first line - 1550 - is this Leonard Digges?



b) 7th line - is this Galileo?



c) the start of the second paragraph - is this Newton? Hooke?



Please confirm that my guesses are correct and amend your article so that it makes sense