Editing Refracting telescope (section)

==Applications and achievements==
[[Image:Great Refractor Potsdam.jpg|thumb|right|300px| The "Große Refraktor" a double telescope with a 80cm (31.5") and 50 cm (19.5") lenses, was used to discover calcium as an interstellar medium in 1904.]]
[[File:Jessica Meir Photography Training.jpg|thumb|Astronaut trains with camera with large lens]]
Refracting telescopes were noted for their use in astronomy as well as for terrestrial viewing. Many early discoveries of the [[Solar System]] were made with singlet refractors.

The use of refracting telescopic optics are ubiquitous in photography, and are also used in Earth orbit.

One of the more famous applications of the refracting telescope was when Galileo used it to discover the four largest moons of Jupiter in 1609. Furthermore, early refractors were also used several decades later to discover Titan, the largest moon of Saturn, along with three more of Saturn's moons.

In the 19th century, refracting telescopes were used for pioneering work on astrophotography and spectroscopy, and the related instrument, the heliometer, was used to calculate the distance to another star for the first time. Their modest apertures did not lead to as many discoveries and typically so small in aperture that many astronomical objects were simply not observable until the advent of long-exposure photography, by which time the reputation and quirks of reflecting telescopes were beginning to exceed those of the refractors. Despite this, some discoveries include the Moons of Mars, a fifth Moon of Jupiter, and many double star discoveries including Sirius (the Dog star). Refractors were often used for positional astronomy, besides from the other uses in photography and terrestrial viewing.
[[File:Spyglass.jpg|thumb|left|Touristic telescope pointed to Matterhorn in Switzerland]]

;Singlets
The Galilean moons and many other moons of the solar system, were discovered with single-element objectives and aerial telescopes.

[[Galileo Galilei]]'s discovered the [[Galilean satellites]] of Jupiter in 1610 with a refracting telescope.<ref name="Bakich_2000">{{cite book |author=Bakich M. E. |year=2000 |url=https://books.google.com/books?id=PE99nOKjbXAC&q=Amalthea&pg=PA221 |title=The Cambridge Planetary Handbook |publisher=Cambridge University Press |pages=220–221 |isbn=9780521632805}}</ref>

The planet Saturn's moon, [[Titan (moon)|Titan]], was discovered on March 25, 1655, by the Dutch astronomer [[Christiaan Huygens]].<ref>{{cite web|url=http://assets.cambridge.org/052179/3483/sample/0521793483ws.pdf|title=Lifting Titan's Veil|publisher=Cambridge|page=4|archive-url=https://web.archive.org/web/20050222073209/http://assets.cambridge.org/052179/3483/sample/0521793483ws.pdf|archive-date=February 22, 2005}}</ref><ref>{{cite web|url=http://antwrp.gsfc.nasa.gov/apod/ap050325.html|title=Titan|work=Astronomy Picture of the Day|publisher=NASA|archive-url=https://web.archive.org/web/20050327011129/http://antwrp.gsfc.nasa.gov/apod/ap050325.html|archive-date=March 27, 2005}}</ref>

;Doublets
In 1861, the brightest star in the night sky, Sirius, was found to have smaller stellar companion using the 18 and half-inch Dearborn refracting telescope.

By the 18th century refractors began to have major competition from reflectors, which could be made quite large and did not normally suffer from the same inherent problem with chromatic aberration. Nevertheless, the astronomical community continued to use doublet refractors of modest aperture in comparison to modern instruments. Noted discoveries include the [[Moons of Mars]] and a fifth moon of Jupiter, [[Amalthea (moon)|Amalthea]].

[[Asaph Hall]] discovered [[Deimos (moon)|Deimos]] on 12 August 1877 at about 07:48 [[Coordinated Universal Time|UTC]] and [[Phobos (moon)|Phobos]] on 18 August 1877, at the [[US Naval Observatory]] in [[Washington, D.C.]], at about 09:14 [[GMT]] (contemporary sources, using the pre-1925 [[Astronomical day|astronomical convention]] that began the day at noon,<ref>{{cite journal |last1=Campbell |first1=W. W. |title=The Beginning of the Astronomical Day |journal=Publications of the Astronomical Society of the Pacific |date=December 1918 |volume=30 |issue=178 |pages=358 |doi=10.1086/122784 |bibcode=1918PASP...30..358C |doi-access=free }}</ref> give the time of discovery as 11 August 14:40 and 17 August 16:06 [[Washington mean time]] respectively).<ref>{{cite journal |title=Notes |journal=The Observatory |date=September 1877 |volume=1 |pages=181–185 |bibcode=1877Obs.....1..181. }}</ref><ref>{{cite journal |last1=Hall |first1=A. |title=Observations of the Satellites of Mars |journal=Astronomische Nachrichten |date=January 1878 |volume=91 |issue=1 |pages=11–14 |doi=10.1002/asna.18780910103 }}</ref><ref name="Morley1989">{{cite journal |last1=Morley |first1=T. A. |title=A catalogue of ground-based astrometric observations of the Martian satellites, 1877-1982 |journal=Astronomy and Astrophysics Supplement Series |date=February 1989 |volume=77 |issue=2 |pages=209–226 |bibcode=1989A&AS...77..209M }}</ref>

The telescope used for the discovery was the {{convert|26|in|cm|adj=on}} refractor (telescope with a lens) then located at [[Foggy Bottom]].<ref>{{cite web|url=http://amazing-space.stsci.edu/resources/explorations/groundup/lesson/scopes/naval/index.php|title=Telescope: Naval Observatory 26-inch Refractor|website=amazing-space.stsci.edu|access-date=29 October 2018}}</ref> In 1893 the lens was remounted and put in a new dome, where it remains into the 21st century.<ref>{{cite web|url=https://www.usno.navy.mil/USNO/about-us/usnos-telescopes/the-26-inch-refractor|archive-url=https://web.archive.org/web/20180322233721/http://www.usno.navy.mil/USNO/about-us/usnos-telescopes/the-26-inch-refractor|url-status=dead|archive-date=22 March 2018|title=The 26-inch "Great Equatorial" Refractor|website=United States Naval Observatory|access-date=29 October 2018}}</ref>

Jupiter's moon Amalthea was discovered on 9 September 1892, by [[Edward Emerson Barnard]] using the [[James Lick telescope|{{convert|36|in|cm}} refractor telescope]] at [[Lick Observatory]].<ref>{{cite journal| doi = 10.1086/101715| last = Barnard| first = E. E.| date = 12 October 1892| title = Discovery and observations of a fifth satellite to Jupiter| journal = The Astronomical Journal| volume = 12| issue = 11| pages = 81–85| bibcode = 1892AJ.....12...81B}}</ref><ref name="Observatory1894">{{cite book|url=https://books.google.com/books?id=BbA2AQAAIAAJ&pg=RA7-PA27|title=A Brief Account of the Lick Observatory of the University of California|author=Lick Observatory|publisher=The University Press|year=1894|page=7–}}</ref> It was discovered by direct visual observation with the doublet-lens refractor.<ref name="Bakich_2000" />

In 1904, one of the discoveries made using Great Refractor of Potsdam (a double telescope with two doublets) was of the [[interstellar medium]].<ref name=":5">{{Cite book|url=https://books.google.com/books?id=VYvQ_8I_kTwC&q=hartmann+interstellar+matter+potsdam&pg=PA154|title=The Cosmic Connection: How Astronomical Events Impact Life on Earth|last=Kanipe|first=Jeff|date=2011-01-27|publisher=Prometheus Books|isbn=9781591028826}}</ref> The astronomer [[Johannes Franz Hartmann|Professor Hartmann]] determined from observations of the binary star [[Mintaka]] in Orion, that there was the element [[calcium]] in the intervening space.<ref name=":5" />

;Triplets

Planet [[Pluto]] was discovered by looking at photographs (i.e. 'plates' in astronomy vernacular) in a [[blink comparator]] taken with a refracting telescope, an astrograph with a 3 element 13-inch lens.<ref>{{Cite web|url=https://lowell.edu/history/the-pluto-telescope/|title=The Pluto Telescope|website=Lowell Observatory|access-date=2019-11-19}}</ref><ref>{{Cite web|url=https://airandspace.si.edu/multimedia-gallery/6074hjpg|title=Pluto Discovery Plate|website=National Air and Space Museum|date=24 June 2016 |access-date=2019-11-19}}</ref>
{{For timeline|Timeline of discovery of Solar System planets and their moons}}