Guido Horn d'Arturo (13 February 1879 – 1 April 1967) was an Italian

astronomer An astronomer is a scientist in the field of astronomy who focuses on a specific question or field outside the scope of Earth. Astronomers observe astronomical objects, such as stars, planets, natural satellite, moons, comets and galaxy, galax ...

born in Trieste, then part of the Austrian Empire. He obtained Italian citizenship after serving as a volunteer in the

Italian army The Italian Army ( []) is the Army, land force branch of the Italian Armed Forces. The army's history dates back to the Italian unification in the 1850s and 1860s. The army fought in colonial engagements in China and Italo-Turkish War, Libya. It ...

during the

First World War World War I or the First World War (28 July 1914 – 11 November 1918), also known as the Great War, was a World war, global conflict between two coalitions: the Allies of World War I, Allies (or Entente) and the Central Powers. Fighting to ...

. To avoid being persecuted as an irredentist by the Austrian authorities, he officially added to his surname Horn that of "d'Arturo" which he used in the war. He was director of the Astronomical Observatory of Bologna from 1921 to 1954, with an interruption of over six years following the persecution for fascist racial laws. In 1931 he founded the magazine ''Coelum'' for the dissemination of astronomy in the society. The

asteroid An asteroid is a minor planet—an object larger than a meteoroid that is neither a planet nor an identified comet—that orbits within the Solar System#Inner Solar System, inner Solar System or is co-orbital with Jupiter (Trojan asteroids). As ...

3744, discovered in 1983, bears the name "Horn-d'Arturo".

Segmented mirror telescope

In the 1930s, Horn d'Arturo created the tessellated telescope, a progenitor of

segmented mirror A segmented mirror is an array of smaller mirrors designed to act as segments of a single large curved mirror. The segments can be either spherical or asymmetric (if they are part of a larger parabolic reflector). They are used as objectives ...

telescopes. In 1932 Horn d'Arturo began to work on a new idea of combining small mirror tassels, to build a larger telescope mirror. The difficulty of building high quality monolithic glass mirrors with diameters bigger than a few meters was becoming apparent during the development of the 5m Palomar telescope. These mirrors were in any case too expensive for the Italian economy, still struggling after the great depression of 1929. Horn's idea was to build smaller mirrors of the same spherical section of the larger one in which they would be combined so that the rays reflected by the single elements would converge in the same focal plane and produce a single image of each star in the field of view. This way, spherical aberration would be eliminated, together with other aberrations characteristic of spherical mirrors: a pioneering idea of active optics, commonly used nowadays in modern telescopes. Specchio-tasselli-horn

In 1935, Horn d'Arturo constructed a 1 m prototype. Some years later in 1952, he assembled a larger 1.8 meter diameter telescope consisting of 61 tassels, which was installed in the astronomical tower in Bologna. More than 17000 photographic plates were obtained by Horn d'Arturo and collaborators who used this telescope for a systematic survey of the local zenithal sky and discovered a dozen of variable stars. Both the prototype and the 1.8 m telescope are exhibited at the at the

University of Bologna The University of Bologna (, abbreviated Unibo) is a Public university, public research university in Bologna, Italy. Teaching began around 1088, with the university becoming organised as guilds of students () by the late 12th century. It is the ...

. The original principle devised by Horn d'Arturo is at the foundation of the new generation of multi-mirror telescopes (or segmented mirrors): the Multiple Mirror Telescope in

Arizona Arizona is a U.S. state, state in the Southwestern United States, Southwestern region of the United States, sharing the Four Corners region of the western United States with Colorado, New Mexico, and Utah. It also borders Nevada to the nort ...

, built in 1979, the twin telescopes of the

Keck Observatory The W. M. Keck Observatory is an astronomical observatory with two telescopes at an elevation of 4,145 meters (13,600 ft) near the summit of Mauna Kea in the U.S. state of Hawaii. Both telescopes have aperture primary mirrors, and, when c ...

in Hawaii, built between 1993 and 1996, consisting of 36 segments 1.8 m each for a total diameter of 10 meters. On

Cerro Armazones Cerro Armazones is a mountain located in the Sierra Vicuña Mackenna of the Chilean Coast Range of the Andes, approximately southeast of Antofagasta in the Antofagasta Region, Chile. The mountain is situated in an ideal location for optical ast ...

in the Atacama Desert in

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work on the dome of the ELT (

Extremely Large Telescope The Extremely Large Telescope (ELT) is an astronomical observatory under construction. When completed, it will be the world's largest optical and near-infrared extremely large telescope. Part of the European Southern Observatory (ESO) agency, ...

), a 39.3 m telescope composed of 798 segments, started in 2017. The

James Webb Space Telescope The James Webb Space Telescope (JWST) is a space telescope designed to conduct infrared astronomy. As the largest telescope in space, it is equipped with high-resolution and high-sensitivity instruments, allowing it to view objects too old, Lis ...

, launched on 25 December 2021, has a primary mirror composed of 18 hexagonal segments for a diameter of 6.5 m The Società Astronomica Italiana (SAIT), and the

Istituto Nazionale di Astrofisica The National Institute for Astrophysics (, or INAF) is an Italian research institute in astronomy and astrophysics, founded in 1999. INAF funds and operates twenty separate research facilities, which in turn employ scientists, engineers and techn ...

(INAF), dedicated the telescope ASTRI (Astrophysics with Mirrors with Italian Replicant Technology), located on the volcano Etna in Sicily, to Horn. On 10 November 2018, with an official ceremony, the telescope was named "ASTRI-Horn".

References

External links

Guido Horn d'Arturo
Biography of Italian astronomers, in ''Polvere di Stelle: the cultural heritage of Italian astronomy''
Le luci di Horn
{{DEFAULTSORT:Horn d'Arturo, Guido 1879 births 1967 deaths 20th-century Italian astronomers Burials at Campo Verano

Segmented mirror telescope

References

Further reading

External links