Geminiano Montanari

Geminiano Montanari (1 June 1633 – 13 October 1687) was an Italian astronomer, lens-maker, and proponent of the experimental approach to science.

He is best known for his observation, made around 1667, that the second-brightest star (called Algol as derived from its name in Arabic) in the constellation of Perseus varied in brightness. It is likely that others had observed this effect before, but Montanari was the first named astronomer to record it. The star's names in Arabic, Hebrew and other languages, all of which have a meaning of "ghoul" or "demon", imply that its unusual behaviour had long been recognised.

Montanari was born in Modena, studied law in Florence, and graduated from the University of Salzburg. In 1662 or 1663 he moved to Bologna, where he drew an accurate map of the Moon using an ocular micrometer of his own making. He also made observations on capillarity and other problems in statics, and suggested that the viscosity of a liquid depended on the shape of its molecules. In 1669 he succeeded Giovanni Cassini as astronomy teacher at the University of Bologna[1] where one of his duties was to compile an astrological almanac. He did so in 1665, but perpetrated a deliberate hoax by writing the almanac entirely at random, to show that predictions made by chance were as likely to be fulfilled as those made by astrology. In the period shortly after Galileo Galilei, experimentalists like Montanari were engaged in a battle against the more mystical views of scientists such as Donato Rossetti.

On 21 March 1676 Montanari reported a sighting of a comet to Edmund Halley.

Montanari's observations of the great comet of 1680 are mentioned twice in the third volume of Newton's Principia.[2]

In 1679 Montanari moved to a teaching post in Padua, but almost all records of this period of his life have been lost. A letter survives from 1682 recording a sighting of Halley's Comet. He also wrote on economics, observing that demand for a particular commodity was fixed, and making comments on coinage and the value of money (1683).

A crater on the Moon, at 45.8S, 20.6W, is named after him.

Geminiano Montanari
Geminiano Montanari.


Montanari - Prostasi fisicomatematica, 1669 - 854259
Prostasi fisicomatematica, 1669
  • Pensieri fisico-matematici (1667)
  • La Livella Diottrica (The Spirit Level) (1674)
  • Trattato mercantile delle monete (1680)
  • Montanari, Geminiano (1667). Pensieri fisico-matematici intorno diversi effetti de' liquidi in cannuccie di vetro e altri vasi. In Bologna: Emilio Maria & fratelli Manolessi. Retrieved 15 June 2015.
  • Montanari, Geminiano (1669). Prostasi fisicomatematica. In Bologna: Emilio Maria & fratelli Manolessi. Retrieved 15 June 2015.


  1. ^ "Montanari, Geminiano". The Galileo Project. Rice University. Retrieved 8 August 2018.
  2. ^ Isaac Newton, The Principia: Mathematical Principles of Natural Philosophy, edited by Bernard I. Cohen and Anne Whitman, Berkeley, University of California Press, 1999, pp. 913-915, 927.

Further reading

  • Gómez López, Susana, Le passioni degli atomi. Montanari e Rossetti: Una polemica tra galileiani, Florence, Leo S. Olschki, 1997.
  • Rotta, Sergio, 'Scienza e "pubblica felicità" in G. Montanari', in Miscellanea Seicento, Florence, Le Monnier, 1971, vol. 2, pp. 65-208.
  • Vanzo, Alberto, 'Experiment and Speculation in Seventeenth-Century Italy: The Case of Geminiano Montanari', Studies in History and Philosophy of Science, 56 (2016), pp. 52-61.

External links



was a common year starting on Saturday of the Gregorian calendar and a common year starting on Tuesday of the Julian calendar, the 1633rd year of the Common Era (CE) and Anno Domini (AD) designations, the 633rd year of the 2nd millennium, the 33rd year of the 17th century, and the 4th year of the 1630s decade. As of the start of 1633, the Gregorian calendar was

10 days ahead of the Julian calendar, which remained in localized use until 1923.



was a common year starting on Wednesday of the Gregorian calendar and a common year starting on Saturday of the Julian calendar, the 1687th year of the Common Era (CE) and Anno Domini (AD) designations, the 687th year of the 2nd millennium, the 87th year of the 17th century, and the 8th year of the 1680s decade. As of the start of 1687, the Gregorian calendar was

10 days ahead of the Julian calendar, which remained in localized use until 1923.


Algol (), designated Beta Persei (β Persei, abbreviated Beta Per, β Per), known colloquially as the Demon Star, is a bright multiple star in the constellation of Perseus and one of the first non-nova variable stars to be discovered.

Algol is a three-star system, consisting of Beta Persei Aa1, Aa2, and Ab - in which the hot luminous primary β Persei Aa1 and the larger, but cooler and fainter, β Persei Aa2 regularly pass in front of each other, causing eclipses. Thus Algol's magnitude is usually near-constant at 2.1, but regularly dips to 3.4 every 2.86 days during the roughly 10-hour-long partial eclipses. The secondary eclipse when the brighter primary star occults the fainter secondary is very shallow and can only be detected photoelectrically.Algol gives its name to its class of eclipsing variable, known as Algol variables.

Algol variable

Algol variables or Algol-type binaries are a class of eclipsing binary stars that are related to the prototype member of this class, β Persei (Beta Persei, Algol) from an evolutionary point of view. An Algol binary is a semidetached binary system where the primary component is an early type, main sequence star that does not fill its Roche lobe, while the cooler, fainter, larger, less massive secondary component lies above the main sequence in a Hertzsprung–Russell diagram and fills the Roche lobe. Early in its history, the secondary star would have been more massive, evolving first to overfill its Roche lobe. After rapid mass exchange, the lobe-filling star became less massive than its companion.When the cooler component passes in front of the hotter one, part of the latter's light is blocked, and the total brightness of the binary, as viewed from Earth, temporarily decreases. This is the primary minimum of the binary. Total brightness may also decrease, but less so, when the hotter component passes in front of the cooler one; this is the secondary minimum.

The period, or time span between two primary minima, is very regular over moderate periods of time (months to years), being determined by the revolution period of the binary, the time it takes for the two components to once orbit around each other. Most Algol variables are quite close binaries, and therefore their periods are short, typically a few days. The shortest known period is 0.1167 days (~2:48 hours, HW Virginis); the longest is 9892 days (27 years, Epsilon Aurigae). Over long periods of time, various effects can cause the period to vary: in some Algol binaries, mass transfer between the closely spaced components of the variable may cause monotonic increases in period; if one component of the pair is magnetically active, the Applegate mechanism may cause recurrent changes in period on the order of ∆P/P ≈ 10−5; magnetic braking or the effects of a third component star in a highly eccentric orbit can cause larger changes in period.Component stars of Algol binary systems have a spherical, or slightly ellipsoidal shape. This distinguishes them from the so-called beta Lyrae variables and W Ursae Majoris variables, where the two components are so close that gravitational effects lead to serious deformations of both stars.

Generally the amplitudes of the brightness variations are of the order of one magnitude, the largest variation known being 3.4 magnitudes (V342 Aquilae). The components may have any spectral type, though in most cases the brighter component is found to have a B, A, F, or G class.

Algol itself, the prototype of this type of variable star, Bayer designation Beta Persei, first had its variability recorded in 1667 by Geminiano Montanari. The mechanism for its being variable was first correctly explained by John Goodricke in 1782.

Many thousands of Algol binaries are now known: the latest edition of the General Catalogue of Variable Stars (2003) lists 3,554 of them (9% of all variable stars).

DM = A detached main-sequence system. Both components are main-sequence stars and neither fills their inner Roche lobe

DS = A detached system with a subgiant. The subgiant does not fill its inner critical surface

GS = A system with one or both giant and supergiant components; one of the components may be a main sequence star

KE = A contact system of early (O-A) spectral type, both components being close in size to their inner critical surfaces.

SD = A semidetached system. One star fills its Roche lobe.

Binary star

A binary star is a star system consisting of two stars orbiting around their common barycenter. Systems of two or more stars are called multiple star systems. These systems, especially when more distant, often appear to the unaided eye as a single point of light, and are then revealed as multiple by other means. Research over the last two centuries suggests that half or more of visible stars are part of multiple star systems.The term double star is often used synonymously with binary star; however, double star can also mean optical double star. Optical doubles are so called because the two stars appear close together in the sky as seen from the Earth; they are almost on the same line of sight. Nevertheless, their "doubleness" depends only on this optical effect; the stars themselves are distant from one another and share no physical connection. A double star can be revealed as optical by means of differences in their parallax measurements, proper motions, or radial velocities. Most known double stars have not been studied adequately to determine whether they are optical doubles or doubles physically bound through gravitation into a multiple star system.

Binary star systems are very important in astrophysics because calculations of their orbits allow the masses of their component stars to be directly determined, which in turn allows other stellar parameters, such as radius and density, to be indirectly estimated. This also determines an empirical mass-luminosity relationship (MLR) from which the masses of single stars can be estimated.

Binary stars are often detected optically, in which case they are called visual binaries. Many visual binaries have long orbital periods of several centuries or millennia and therefore have orbits which are uncertain or poorly known. They may also be detected by indirect techniques, such as spectroscopy (spectroscopic binaries) or astrometry (astrometric binaries). If a binary star happens to orbit in a plane along our line of sight, its components will eclipse and transit each other; these pairs are called eclipsing binaries, or, as they are detected by their changes in brightness during eclipses and transits, photometric binaries.

If components in binary star systems are close enough they can gravitationally distort their mutual outer stellar atmospheres. In some cases, these close binary systems can exchange mass, which may bring their evolution to stages that single stars cannot attain. Examples of binaries are Sirius, and Cygnus X-1 (Cygnus X-1 being a well-known black hole). Binary stars are also common as the nuclei of many planetary nebulae, and are the progenitors of both novae and type Ia supernovae.

Capillary action

Capillary action (sometimes capillarity, capillary motion, capillary effect, or wicking) is the ability of a liquid to flow in narrow spaces without the assistance of, or even in opposition to, external forces like gravity. The effect can be seen in the drawing up of liquids between the hairs of a paint-brush, in a thin tube, in porous materials such as paper and plaster, in some non-porous materials such as sand and liquefied carbon fiber, or in a cell. It occurs because of intermolecular forces between the liquid and surrounding solid surfaces. If the diameter of the tube is sufficiently small, then the combination of surface tension (which is caused by cohesion within the liquid) and adhesive forces between the liquid and container wall act to propel the liquid.

Domenico Guglielmini

Domenico Guglielmini (Bologna, 27 September 1655 - Padoa, 27 July 1710) was an Italian mathematician, chemist and physician.He lived and worked with success in Bologna and Padoa rising to a notable level of prominence.

June 1

June 1 is the 152nd day of the year (153rd in leap years) in the Gregorian calendar. There are 213 days remaining until the end of the year.

Jurin's law

One of the most common fluid mechanical effects that is often explored in micro fluids is capillarity i.e the induced motion of liquids in small channels of which the most simplest case is capillary rise or Jurin's law, named after James Jurin who discovered it in 1718. His quantitative law suggests that the maximum height of a capillary tube is inversely proportional to the diameter. The difference in height between the surroundings of the tube and the inside and the shape of the meniscus, are caused by capillary action. The mathematical expression of this law can be derived directly from hydrostatic principles and from Young–Laplace equation. Jurin's law allows the measurement of the surface tension of a liquid and can be used to derive the capillary length.

List of Italian scientists

This is a list of notable Italian scientists organized by the era in which they were active.

List of variable stars

There are over 41,638 known variable stars (2008), with more being discovered regularly, so a complete list of every single variable is impossible at this place (cf. GCVS). The following is a list of variable stars that are well-known, bright, significant, or otherwise interesting.

Montanari (surname)

Montanari is an Italian surname meaning mountaineer or highlander. Its highest concentration occurs in the region of Emilia Romagna.Some notable people with this surname include:

Antonio Montanari, Italian violinist and composer

Christian Montanari, Sammarinese racing car driver

Geminiano Montanari, Italian astronomer

Giuseppe Montanari, Italian painter

Marcello Montanari, Italian professional football

Massimo Montanari, professor or Medieval History at Bologna University and writer on the history and culture of food

Richard Montanari, American crime writer

Wolfango Montanari, Italian former sprinter

October 13

October 13 is the 286th day of the year (287th in leap years) in the Gregorian calendar. There are 79 days remaining until the end of the year.

Paolo Del Buono

Paolo Del Buono (1625-1659) was an Italian scientific instrument maker.

A Florentine disciple of Famiano Michelini (1604-1665), Paolo Del Buono received his doctorate from the University of Pisa in 1649. In 1655, he went to Germany to enter the service of Ferdinand III (Emperor from 1637 to 1657) and was appointed director of the Imperial Mint. During his stay, with his student Geminiano Montanari (1633-1687), he visited the imperial mines in the Carpathian mountains and invented a method of extracting water. Del Buono performed wide-ranging research in physics and experimental science. Paolo and his brother Candido Del Buono (1618-1676) both belonged to the Accademia del Cimento, with whom Paolo corresponded from Germany.He is also noted for an experiment in 1657 which showed the incompessibility of water where water compressed in a gold shell by a screw seeped through pores in the gold, and for introducing into Tuscany an Egyptian method of raising chickens whereby the eggs are hatched by gradually introducing heat to them.


A star is type of astronomical object consisting of a luminous spheroid of plasma held together by its own gravity. The nearest star to Earth is the Sun. Many other stars are visible to the naked eye from Earth during the night, appearing as a multitude of fixed luminous points in the sky due to their immense distance from Earth. Historically, the most prominent stars were grouped into constellations and asterisms, the brightest of which gained proper names. Astronomers have assembled star catalogues that identify the known stars and provide standardized stellar designations. However, most of the estimated 300 sextillion (3×1023) stars in the Universe are invisible to the naked eye from Earth, including all stars outside our galaxy, the Milky Way.

For at least a portion of its life, a star shines due to thermonuclear fusion of hydrogen into helium in its core, releasing energy that traverses the star's interior and then radiates into outer space. Almost all naturally occurring elements heavier than helium are created by stellar nucleosynthesis during the star's lifetime, and for some stars by supernova nucleosynthesis when it explodes. Near the end of its life, a star can also contain degenerate matter. Astronomers can determine the mass, age, metallicity (chemical composition), and many other properties of a star by observing its motion through space, its luminosity, and spectrum respectively. The total mass of a star is the main factor that determines its evolution and eventual fate. Other characteristics of a star, including diameter and temperature, change over its life, while the star's environment affects its rotation and movement. A plot of the temperature of many stars against their luminosities produces a plot known as a Hertzsprung–Russell diagram (H–R diagram). Plotting a particular star on that diagram allows the age and evolutionary state of that star to be determined.

A star's life begins with the gravitational collapse of a gaseous nebula of material composed primarily of hydrogen, along with helium and trace amounts of heavier elements. When the stellar core is sufficiently dense, hydrogen becomes steadily converted into helium through nuclear fusion, releasing energy in the process. The remainder of the star's interior carries energy away from the core through a combination of radiative and convective heat transfer processes. The star's internal pressure prevents it from collapsing further under its own gravity. A star with mass greater than 0.4 times the Sun's will expand to become a red giant when the hydrogen fuel in its core is exhausted. In some cases, it will fuse heavier elements at the core or in shells around the core. As the star expands it throws a part of its mass, enriched with those heavier elements, into the interstellar environment, to be recycled later as new stars. Meanwhile, the core becomes a stellar remnant: a white dwarf, a neutron star, or if it is sufficiently massive a black hole.

Binary and multi-star systems consist of two or more stars that are gravitationally bound and generally move around each other in stable orbits. When two such stars have a relatively close orbit, their gravitational interaction can have a significant impact on their evolution. Stars can form part of a much larger gravitationally bound structure, such as a star cluster or a galaxy.

Timeline of stellar astronomy

Timeline of stellar astronomy

2300 BC — First great period of star naming in China.

134 BC — Hipparchus creates the magnitude scale of stellar apparent luminosities

185 AD — Chinese astronomers become the first to observe a supernova, the SN 185

964 — Abd al-Rahman al-Sufi (Azophi) writes the Book of Fixed Stars, in which he makes the first recorded observations of the Andromeda Galaxy and the Large Magellanic Cloud, and lists numerous stars with their positions, magnitudes, brightness, and colour, and gives drawings for each constellation

1000s (decade) — The Persian astronomer, Abū Rayhān al-Bīrūnī, describes the Milky Way galaxy as a collection of numerous nebulous stars

1006 — Ali ibn Ridwan and Chinese astronomers observe the SN 1006, the brightest stellar event ever recorded

1054 — Chinese and Arab astronomers observe the SN 1054, responsible for the creation of the Crab Nebula, the only nebula whose creation was observed

1181 — Chinese astronomers observe the SN 1181 supernova

1580 — Taqi al-Din measures the right ascension of the stars at the Constantinople Observatory of Taqi ad-Din using an "observational clock" he invented and which he described as "a mechanical clock with three dials which show the hours, the minutes, and the seconds"

1596 — David Fabricius notices that Mira's brightness varies

1672 — Geminiano Montanari notices that Algol's brightness varies

1686 — Gottfried Kirch notices that Chi Cygni's brightness varies

1718 — Edmund Halley discovers stellar proper motions by comparing his astrometric measurements with those of the Greeks

1782 — John Goodricke notices that the brightness variations of Algol are periodic and proposes that it is partially eclipsed by a body moving around it

1784 — Edward Pigott discovers the first Cepheid variable star

1838 — Thomas Henderson, Friedrich Struve, and Friedrich Bessel measure stellar parallaxes

1844 — Friedrich Bessel explains the wobbling motions of Sirius and Procyon by suggesting that these stars have dark companions

1906 — Arthur Eddington begins his statistical study of stellar motions

1908 — Henrietta Leavitt discovers the Cepheid period-luminosity relation

1910 — Ejnar Hertzsprung and Henry Norris Russell study the relation between magnitudes and spectral types of stars

1924 — Arthur Eddington develops the main sequence mass-luminosity relationship

1929 — George Gamow proposes hydrogen fusion as the energy source for stars

1938 — Hans Bethe and Carl von Weizsäcker detail the proton-proton chain and CNO cycle in stars

1939 — Rupert Wildt realizes the importance of the negative hydrogen ion for stellar opacity

1952 — Walter Baade distinguishes between Cepheid I and Cepheid II variable stars

1953 — Fred Hoyle predicts a carbon-12 resonance to allow stellar triple alpha reactions at reasonable stellar interior temperatures

1961 — Chūshirō Hayashi publishes his work on the Hayashi track of fully convective stars

1963 — Fred Hoyle and William A. Fowler conceive the idea of supermassive stars

1964 — Subrahmanyan Chandrasekhar and Richard Feynman develop a general relativistic theory of stellar pulsations and show that supermassive stars are subject to a general relativistic instability

1967 — Eric Becklin and Gerry Neugebauer discover the Becklin-Neugebauer Object at 10 micrometres

1977 — (May 25) The Star Wars film is released and became a worldwide phenomenon, boosting interests in stellar systems.

2012 — (May 2) First visual proof of existence of black-holes. Suvi Gezari's team in Johns Hopkins University, using the Hawaiian telescope Pan-STARRS 1, publish images of a supermassive black hole 2.7 million light-years away swallowing a red giant.

Variable star

A variable star is a star whose brightness as seen from Earth (its apparent magnitude) fluctuates.

This variation may be caused by a change in emitted light or by something partly blocking the light, so variable stars are classified as either:

Intrinsic variables, whose luminosity actually changes; for example, because the star periodically swells and shrinks.

Extrinsic variables, whose apparent changes in brightness are due to changes in the amount of their light that can reach Earth; for example, because the star has an orbiting companion that sometimes eclipses it.Many, possibly most, stars have at least some variation in luminosity: the energy output of our Sun, for example, varies by about 0.1% over an 11-year solar cycle.

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