60 Fun Facts About Telescopes

From which language do the roots of the word 'telescope' come, meaning 'far' and 'to look'?

Tele means 'far' and skopein 'to see'; Galileo himself had used the Latin word perspicillum in the Starry Messenger.

Who coined the word 'telescope' in 1611, at a banquet honouring Galileo at the Accademia dei Lincei?

Demisiani was a Greek mathematician and poet; Prince Federico Cesi hosted the banquet to make Galileo a member of the academy.

In which country were the first known practical telescopes invented at the start of the 17th century?

They were refracting telescopes with glass lenses, used for both terrestrial purposes and astronomy.

Which Middelburg spectacle-maker filed the earliest known telescope patent application in 1608?

The patent was refused because others claimed the same invention, but the Dutch government paid him handsomely for copies of the instrument.

How did the October 1608 Dutch patent application describe the new instrument?

A few weeks later another Dutch instrument-maker, Jacob Metius, also applied for a patent.

In which city did Galileo first hear of the 'Dutch perspective glass' in June 1609?

He said he worked out how to build one the first night after returning to Padua and made his first telescope the next day.

What combination of lenses did Galileo's telescope use?

The design gives an upright image but a narrow field of view; Kepler's convex-convex design gives a wider, inverted view.

Which astronomer described in 1611 a telescope with a convex objective and a convex eyepiece?

The Keplerian design has a much larger field of view than Galileo's, but the image is upside down.

Using a Keplerian telescope he built himself, Christiaan Huygens discovered which moon in 1655?

Four years later his Systema Saturnium gave the first correct explanation of Saturn's ring, based on the same instrument.

What were the very long tubeless refractors built by 17th-century astronomers like Hevelius called?

Long focal lengths reduced chromatic aberration; Adrien Auzout made instruments with focal lengths up to 600 feet.

Who built the first practical reflecting telescope in 1668?

Gregory had described a mirror telescope in 1663 but could not find an optician to build it; Hooke built the first Gregorian in 1673.

What tin-copper alloy was standard for telescope mirrors into the 19th century?

It tarnished quickly and reflected poorly, so mirrors had to be re-polished and often re-figured.

What is the hallmark feature of a Newtonian telescope?

The flat secondary reflects the light at 90 degrees near the primary mirror's focus.

In 1672 Laurent Cassegrain described a reflector in which light passes through what?

A small convex secondary mirror sends the light back through the hole; the Ritchey–Chrétien variant is used by Hubble.

Which Englishman built the first achromatic-lens telescope in 1733 but never publicised it?

Dollond learned of the invention and produced achromatic telescopes commercially from 1758; a court case later admitted Hall was the first inventor.

What did an achromatic lens combine to bring red and blue light to the same focus?

Euler had even proposed an objective of glass and water; Dollond disputed his theory but built the practical version.

John Hadley, better known for inventing the octant, advanced reflecting telescopes in 1721 by doing what?

His 6-inch reflector matched a 7.5-inch aerial telescope in tests at the Royal Society, showing Newton's idea worked in practice.

William Herschel began grinding telescope mirrors around 1774 while working in Bath as what?

By 1789 he had built his 40-foot telescope with a 49-inch mirror at Observatory House in Slough.

In the 'Herschelian' design, how did Herschel avoid the light loss caused by a diagonal secondary?

Speculum mirrors reflected so poorly that removing the diagonal made a real difference in brightness.

Who built the 72-inch 'Leviathan of Parsonstown', the world's largest telescope from 1845 to 1917?

Built at Birr Castle in Ireland, it revealed the spiral form of galaxies.

Which French physicist introduced the process of silvering glass mirrors for telescopes in 1857?

Aluminised coatings, which last far longer, followed in 1932.

In which US state is Yerkes Observatory, home to the world's largest refracting telescope when it opened in 1897?

It was shown at Chicago's World's Columbian Exposition before installation at Williams Bay; the observatory was founded by George Ellery Hale.

Roughly what is the practical maximum diameter for a refracting telescope's lens?

Which is why virtually every large research telescope built since 1900 has been a reflector.

The 100-inch Hooker telescope, the world's largest from 1917 to 1949, is on which California mountain?

Edwin Hubble used it to show that nebulae lay far beyond the Milky Way and that the universe is expanding.

The 200-inch Hale Telescope at Palomar has a primary mirror made of which glass?

Corning Glass Works cast the honeycomb, low-expansion disc; the telescope saw first light in January 1949 under Edwin Hubble.

Which telescope ended the Hale Telescope's reign as the world's largest in 1976?

Hale then remained the second largest until Keck 1 in Hawaii in 1993.

What is the general term for a telescope that uses both mirrors and lenses to form its image?

The Schmidt camera, invented by Bernhard Schmidt in 1930, is a famous wide-field example.

Who invented the simple alt-azimuth reflector beloved of amateur astronomers, the Dobsonian, in 1956?

It is essentially a Newtonian on a plywood box mount.

Which Bell Labs engineer first detected radio waves from space in 1932?

He had been asked to find sources of static that might interfere with radiotelephone service.

Where did radio amateur Grote Reber build the first purpose-built radio telescope in 1937?

The sky survey he made with it is often considered the beginning of radio astronomy.

What is combining signals from several dishes into a virtual high-resolution telescope called?

Such multi-dish arrays are astronomical interferometers, and with space-based VLBI the virtual aperture can exceed the Earth's diameter.

For how many years was Arecibo the world's largest single-aperture telescope?

Completed in 1963, it was surpassed by China's FAST in 2016 and collapsed in December 2020.

The climactic fight of which James Bond film was staged at the Arecibo Telescope?

The dish also appeared in the film Contact; the NSF decided in 2022 not to rebuild it.

China's FAST radio telescope, the world's largest single dish, is nicknamed what?

Its 500-metre dish sits in a natural karst depression in Guizhou and has an active surface of 4,500 movable panels.

The Event Horizon Telescope published the first image of a black hole in April 2019. In which galaxy was it?

The image of our own galaxy's black hole, Sagittarius A*, followed in May 2022.

The Very Large Telescope's units Antu, Kueyen, Melipal and Yepun take their names from which language?

They can be combined as an interferometer, and made the first direct image of an exoplanet.

The 10.4-metre Gran Telescopio Canarias, the largest single-aperture optical telescope, is on which island?

It sits at the Roque de los Muchachos Observatory and was inaugurated by King Juan Carlos I in July 2009.

What is the diameter of the segmented primary mirror of ESO's Extremely Large Telescope in Chile?

It will gather 100 million times more light than the human eye, about ten times more than today's largest optical telescopes.

Why must X-ray and gamma-ray telescopes be placed on satellites or high-altitude balloons?

X-ray telescopes use grazing-incidence 'Wolter' mirrors that reflect the rays by only a few degrees.

Who outlined in 1952 the three ways to build an X-ray telescope from grazing mirrors?

The Einstein Observatory, ROSAT and Chandra all use Wolter-type optics.

NASA's Chandra X-ray Observatory, launched in 1999, is named after which Nobel-winning astrophysicist?

It flew on Space Shuttle Columbia and circles Earth in a 64-hour orbit.

The Hubble Space Telescope's primary mirror is how wide?

The original plan for 3 metres was cut to save money; James Webb's segmented mirror is 6.5 metres.

What flaw was found in Hubble's main mirror after its 1990 launch?

The optics were corrected by the STS-61 servicing mission in December 1993.

Which Cassegrain telescope design, invented around 1910, does Hubble use for its wider field of view?

It was not widely adopted until after 1950.

The Spitzer Space Telescope, active from 2003 to 2020, observed in which part of the spectrum?

It was the third infrared space telescope after IRAS and ISO, and one of NASA's four Great Observatories.

What did NASA's Kepler space telescope, launched in 2009, monitor in order to find exoplanets?

It was retired in October 2018 when its fuel ran out, after nine and a half years.

On what date was the James Webb Space Telescope launched?

It rode an Ariane 5 from Kourou, French Guiana, and reached its L2 halo orbit in January 2022.

The Webb telescope's 6.5-metre primary mirror has 18 hexagonal segments of which metal?

The gold gives infrared reflectivity; the whole telescope must stay below 50 kelvin behind its five-layer sunshield.

Roughly how far from Earth is the Sun–Earth L2 point where the James Webb Space Telescope operates?

Objects there orbit the Sun in step with the Earth, keeping Sun, Earth and Moon all on the same side of the sunshield.

James Webb, after whom the telescope is named, held what job from 1961 to 1968?

He ran the agency through Mercury, Gemini and Apollo; the project was renamed from Next Generation Space Telescope in 2002.

The Vera C. Rubin Observatory's camera, the largest ever built, has what resolution?

Its 8.4-metre Simonyi Survey Telescope images the whole southern sky every few nights for a ten-year time-lapse.

Which Estonian-German optician invented the wide-field survey camera that bears his name in 1930?

Schmidt telescopes at Palomar, Siding Spring and ESO provided most all-sky photographic surveys from 1950 to 2000.

What two advantages did a parabolic mirror promise over a lens as a telescope objective?

That promise drove the many attempts to build reflectors in the decades after the refractor was invented.

Which Space Shuttle carried the Hubble Space Telescope into orbit in April 1990?

The launch had been planned for 1983 but slipped because of technical problems, budget issues and the 1986 Challenger disaster.

Whose 1946 paper on an 'extraterrestrial observatory' began the history of the Hubble telescope?

Spitzer later had NASA's infrared space telescope named after him; the Hubble itself was named for Edwin Hubble in 1983.

Which company ground Hubble's famously flawed primary mirror?

The investigating commission blamed the failings primarily on Perkin-Elmer; one lens in its test equipment was out of position by 1.3 mm.

How many Space Shuttle servicing missions were flown to Hubble between 1993 and 2009?

The first, aboard Endeavour in December 1993, fixed the mirror flaw; the last, on Atlantis in May 2009, installed Wide Field Camera 3.

In which city is the Space Telescope Science Institute, which selects Hubble's targets?

It sits on the Johns Hopkins Homewood campus; Goddard Space Flight Center, 48 km south, actually controls the spacecraft.

Which rocket launched the James Webb Space Telescope from French Guiana?

The sunshield had to be folded twelve times to fit the rocket's 4.57-metre-wide payload fairing.

How many layers make up the James Webb Space Telescope's sunshield?

Each layer is Kapton E film about 0.1 mm thick, coated with aluminium; the shield has an effective SPF of about 1,000,000.