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The earliest known working telescopes appeared in 1608 and are credited to Hans Lippershey. Among many others who claimed to have made the discovery were Zacarias Janssen, spectacle-maker in Middelburg, and Christiaan Huygens of Alkmaar. The design of these early refracting telescopes consisted of a convex objective lens and a concave eyepiece. Galileo used this design the following year. In 1611, Johannes Kepler described how a telescope could be made with a convex objective and eyepiece lens and by 1655 astronomers such as Christiaan Huygens were building powerful but extremely large and unwieldy Keplerian telescopes with compound eyepieces. Hans Lippershey is the earliest person documented to have applied for a patent for the device.
Isaac Newton is credited with building the first "practical" reflector in 1668 with a design that incorporated a small flat diagonal mirror to reflect the light to an eyepiece mounted on the side of the telescope. Laurent Cassegrain in 1672 described the design of a reflector with a small convex secondary mirror to reflect light through a central hole in the main mirror.
The achromatic lens, which greatly reduced color aberrations in objective lenses and allowed for shorter and more functional telescopes, first appeared in a 1733 telescope made by Chester Moore Hall, who did not publicize it. John Dollond independently developed achromatic lenses and produced telescopes using them in commercial quantities, starting in 1758.
Important developments in reflecting telescopes were John Hadley's production of larger paraboloidal mirrors in 1721; the process of silvering glass mirrors introduced by Léon Foucault in 1857; and the adoption of long lasting aluminized coatings on reflector mirrors in 1932. Almost all of the large optical research telescopes used today are reflectors.
The era of radio telescopes (along with radio astronomy) was born with Karl Guthe Jansky's serendipitous discovery of astronomical radio source in 1931. Many types of telescopes were developed in the 20th century for a wide range of wavelengths from radio to gamma-rays.
Optical telescopes
Invention
Optical foundations
See also: History of opticsLenses and their properties were known well before the invention of the optical telescope; simple lenses made from rock crystal have been known from before recorded history. Ptolemy (in his work Optics written in the 2nd century AD) wrote about the properties of light including reflection, refraction, and color. During the 10th century, one of Ptolemy's most capable scholars named Ibn Sahl, was to make some of the most refined descriptions in respect to optics at the time. The effects of pinhole and the magnifying properties of concave lenses were described by the Arabian astronomer-physicist, Ibn al-Haytham, around 1020. The Latin translation of his main work the Kitab al-Manazir ( Book of Optics ) influenced European scientists such as Johannes Kepler—and the work of Roger Bacon.
It was approximately from the 12th century in Europe that 'reading stones' (magnifying lenses placed on the reading material) were well documented—as well as the use of lenses as burning glasses. It is generally considered that spectacles for correcting long sightedness with convex lenses were invented in Northern Italy in the late 13th to early 14th century, and the invention of the use of concave lenses to correct near-sightedness is ascribed to Nicholas of Cusa in 1451. Thus, early knowledge of lenses and the availability of lenses for spectacles from the 13th century onwards through the 16th century means that it was possible for many individuals to discover the principles of a telescope using a combination of concave or concave and convex lenses; in the 13th century, Robert Grosseteste wrote several scientific treatises between 1230 and 1235, including De Iride ( Concerning the Rainbow ), in which he said:....:)
" This part of optics, when well understood, shows us how we may make things a very long distance off appear as if placed very close, and large near things appear very small, and how we may make small things placed at a distance appear any size we want, so that it may be possible for us to read the smallest letters at incredible distances... "
Roger Bacon was a pupil of Grosseteste at Oxford, and is frequently stated as having described a magnifying device in the 13th century, however it is not certain if he built a working model.
Pre 17th century developments
There is some documentary evidence, but no surviving designs or physical evidence, that the principles of telescopes were known in the late 16th century. Writings by John Dee and Thomas Digges in England in 1570 and 1571, respectively ascribe the use of both reflecting and refracting telescopes to Thomas' father Leonard Digges, and it is independently confirmed by a report by William Bourne in approximately 1580. They may have been experimental devices and were never widely reported or reproduced. Thomas Digges describes his father's device as follows:
" But to leave these celestial causes and things done of antiquity long ago, my father by his continual painful practices, assisted with demonstrations Mathematical, was able, and sundry times hath by proportional Glasses duly situate in convenient angles, not only discovered things far off, read letters, numbered pieces of money with the very coin and superscription thereof, cast by some of his friends of purpose upon downs in open fields, but also seven miles off declared what hath been done at that instant in private places ."
Although Digges may have created a rudimentary instrument involving lenses and mirrors, the optical performance required to see the details of coins lying about in fields, or private activities seven miles away, was far beyond the technology of the time.
In Italy, Giambattista della Porta also described a possible telescope as early as 1586 when he wrote in a letter," ...to make glasses that can recognize a man several miles away ." In his Natural Magic published in 1589 he wrote:
" With a Concave lens you shall see small things afar off very clearly. With a Convex lens, things nearer to be greater, but more obscurely. If you know how to fit them both together, you shall see both things afar off, and things near hand, both greater and clearly ."
Della Porta was preoccupied with other things at the time and thought the idea of a "telescope" unimportant. Similar claims have been made about Taqi al-Din (1526–1585) and Juan Roget (died before 1624) inventing early telescope-like devices.
The first known telescopes
The practical exploitation of the instrument was certainly achieved and came to public attention in the Netherlands at about 1608, but the credit of the original invention has been claimed on behalf of three individuals: Hans Lippershey and Sacharias Jansen—spectacle-makers in Middelburg, and Jacob Metius of Alkmaar (also known as Jacob Adriaanszoon). Hans Lippershey was credited with creating and disseminating designs for the first practical telescope—later applying to the States-General of the Netherlands on October 2, 1608, for a patent for an instrument " for seeing things far away as if they were nearby ," (beating Jacob Metius's patent by a few weeks). Lippershey failed to receive a patent since the same claim for invention had been made by other spectacle-makers. Lippershey was handsomely rewarded by the Dutch government for copies of his design. Sacharias Jansen's design for a telescope may have pre-dated Lippershey and Metius, but the invention was never widely publicized.
The original Dutch telescopes were composed of a convex and a concave lens- telescopes that are constructed this way do not invert the image. Lippershey's original design had only 3x magnification. Telescopes seem to have been made in the Netherlands in considerable numbers soon after the date of their invention, and rapidly found their way all over Europe.
Galileo happened to be in Venice in June 1609 and there heard of the "Dutch perspective glass" by means of which distant objects appeared nearer and larger. Galileo states that he solved the problem of the construction of a telescope the first night after his return to Padua from Venice and made his first telescope the next day by fitting a convex lens in one extremity of a leaden tube and a concave lens in the other one. A few days afterwards, having succeeded in making a better telescope than the first, he took it to Venice where he communicated the details of his invention to the public and presented the instrument itself to the doge Leonardo Donato, who was sitting in full council. The senate in return settled him for life in his lectureship at Padua and doubled his salary. Galileo may thus claim to have invented the telescope independently, but not until he had heard that others had done so.
Galileo devoted his time to improving and perfecting the telescope and soon succeeded
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