Before the creation of the earliest known telescope, which first surfaced in the Netherlands in 1608 and for which an application for a patent was made by eyeglass manufacturer Hans Lippershey, the history of the telescope may be traced. Even though Lippershey didn’t get his patent, word of the creation quickly spread throughout Europe. These early refracting telescopes have a convex objective lens and a concave eyepiece as its design elements. The following year, Galileo enhanced this concept and used it in astronomy. Johannes Kepler explained how to construct a telescope with a convex objective lens and convex eyepiece lens in 1611. By 1655, astronomers like Christiaan Huygens were constructing cumbersome Keplerian telescopes with compound eyepieces that were powerful but cumbersome.
With a design that included a small flat diagonal mirror to reflect the light to an eyepiece set on the side of the telescope, Isaac Newton is credited with creating the first reflector in 1668. A reflector having a small convex secondary mirror to reflect light through a central hole in the main mirror was reported by Laurent Cassegrain in 1672.
The achromatic lens had its debut in a 1733 telescope created by Chester Moore Hall, who did not make it widely known. This lens dramatically decreased color aberrations in objective lenses and enabled for shorter and more practical telescopes. When John Dollond learned about Hall’s invention, he started utilizing it to make telescopes in large quantities starting in 1758.
The fabrication of larger paraboloidal mirrors by John Hadley in 1721, the use of glass mirror silvering by Léon Foucault in 1857, and the introduction of durable aluminized coatings on reflector mirrors in 1932 were all significant advancements in reflecting telescopes. The Ritchey-Chretien Cassegrain reflector, which is used in many modern telescopes, including the Hubble Space Telescope, was developed in 1910 but did not gain widespread acceptance until after 1950. This design offers a broader field of vision than a traditional Cassegrain.
Reflectors had issues with speculum metal mirrors between the years 1850 and 1900, and many “Great Refractors” with apertures between 60 cm and 1 meter were constructed, culminating in the Yerkes Observatory refractor in 1897; however, beginning in the early 1900s, a series of increasingly large reflectors with glass mirrors were constructed, including the Mount Wilson 60-inch (1.5 meter), the 100-inch (2.5 meter) Hooker Telescope (1917), Between 1975 and 1985, a number of 4-metre class (160 inch) telescopes were constructed on prime higher altitude sites, such as Hawaii and the Chilean desert. A new generation of even larger telescopes, beginning with the 10-meter (400-inch) Keck telescopes in 1993/1996 and a number of 8-meter telescopes like the ESO Very Large Telescope, Gemini Observatory, and Subaru Telescope, were made possible by the development of the computer-controlled alt-azimuth mount in the 1970s and active optics in the 1980s.
Karl Guthe Jansky’s accidental discovery of an astronomical radio source in 1931 marked the beginning of the radio telescope era (together with radio astronomy). The 20th century saw the development of numerous telescope types for a variety of wavelengths, from radio to gamma rays. After 1960, the development of space observatories made it feasible to observe various bands that were otherwise inaccessible from the ground, such as X-rays and longer wavelength infrared bands.
