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Alejandro Gangui

Publications and source records attributed to Alejandro Gangui.

At least 55 records · Page 3Linked to original sources
arXiv2016

Fixing the shadows while moving the gnomon

It is a common practice to fix a vertical gnomon and study the moving shadow cast by it. This shows our local solar time and gives us a hint regarding the season in which we perform the observation. The moving shadow can also tell us our latitude with high precision. In this paper we propose to exchange the roles and while keeping the shadows fixed on the ground we will move the gnomon. This lets us understand in a simple way the relevance of the tropical lines of latitude and the behavior of shadows in different locations. We then put these ideas into practice using sticks and threads during a solstice on two sites located on opposite sides of the Tropic of Capricorn.

physics.pop-ph↗
arXiv2016

Archaeoastronomy and the orientation of old churches

Cultural astronomy is an interdisciplinary area of research that studies how perceptions and concepts related to the sky are part of the worldview of a culture. One of its branches, archaeoastronomy, focuses on the material remains of past peoples and tries to investigate their practices and astronomical knowledge. In this context, the orientation of Christian churches is now considered a distinctive feature of their architecture that repeats patterns from early Christian times. There is a general tendency to align their altars in the solar range, with preference for orientations towards the east. Here we present recent data from our measurements of astronomical orientations of old churches located in two --geographically and culturally-- very distant regions, and we discuss the results in the light of the historical and cultural knowledge surrounding these temples.

physics.hist-ph↗
arXiv2016

The scientific impact of Einstein's visit to Argentina, in 1925

The arrival of Albert Einstein in Argentina in 1925 had an impact, equally relevant, on the scientific community and on the general public. In this paper we discuss that visit from three different perspectives. Firstly, we consider the conditions that allowed for such visit to be possible. Then we focus on the institutional actors that facilitated it, as well as on the expertise and written references on topics related to relativity theory circulating at the time in the local community. In the last section we consider the implications of that visit for the local scientific environment.

physics.hist-ph↗
arXiv2015

Ars combinatoria and cosmological models: interactions and survival in a Cuzco school painting of the XVIII century

"The Lord made me a very great favor in an imaginary vision" wrote Maria de Agreda in the seventeenth century, "His Majesty put me at the foot of a beautiful Ladder, and showed me I had to climb it." These words refer to the spiritual ascent, present in the Judeo-Christian tradition, and crystallized in the visions of prophets and Catholic saints. Genesis (18: 10-22) narrates that Jacob, going to Haran, slept on some stones and saw a ladder between heaven and earth along which angels were ascending and descending. From this dream, the symbolic union between heaven and earth has been figured with stairs, ascribing to it different meanings over the centuries. On the steps of the ladder people saw a metaphor for the graduality of ascent; Benedict used a ladder of twelve steps of humility in his Regula, and in the seventh century AD John Climacus, Bishop of Sinai, established a thirty-step Scala Paradisi of meditation leading to God. In this work we discuss the historical echoes of the Benedictine rule, together with Climacus' voice in the desert and the visualization of celestial mysteries, in the case of the Cuzco school painting Allegory of the firmament, with the representation of the planets' seven heavens (XVIII century). In this way we try and analyze the intersection between science and mysticism in the representation of the heavenly stairs, in order to show the cultural anchorage of the symbology employed in these cases [abridged].

physics.hist-ph↗
arXiv2015

From the Scale Model of the Sky to the Armillary Sphere

It is customary to employ a semi-spherical scale model to describe the apparent path of the Sun across the sky, whether it be its diurnal motion or its variation throughout the year. A flat surface and three bent semi-rigid wires (representing the three solar arcs during solstices and equinoxes) will do the job. On the other hand, since very early times, there have been famous armillary spheres built and employed by the most outstanding astronomers for the description of the celestial movements. In those instruments, many of them now considered true works of art, Earth lies in the center of the cosmos and the observer looks at the whole "from the outside." Of course, both devices, the scale model of the sky and the armillary sphere, serve to represent the movement of the Sun, and in this paper we propose to show their equivalence by a simple construction. Knowing the basics underlying the operation of the armillary sphere will give us confidence to use it as a teaching resource in school.

physics.pop-ph↗
arXiv2015

Free the Globe

The parallel globe is an old, very simple and ingenious device that, when systematically employed in astronomy classes, becomes a teaching tool with great potential. Properly oriented according to the local meridian, this instrument allows us to follow the shadows in any region of the Earth that is illuminated by the Sun, as well as offering a clear view of the terminator, the fast-moving grey line that divides the day from the night on our planet. With knowledge of the shadows, it is possible to estimate the latitude of a site and to infer local solar time anywhere in the planet's sunlit hemisphere. Furthermore, by using the parallel globe we may understand simply the existence of regions in which objects sometimes do not cast shadows, and also other regions which, on the contrary, sometimes become "long-shadow" countries. In this work, we first review the device and the basics of its assembly and operation. In the second part, we describe in detail some activities targeted to facilitate its use in the classroom, which our research group has been developing during teacher training workshops.

physics.ed-ph↗
arXiv2014

The Barolo Palace: medieval astronomy in the streets of Buenos Aires

Cultural heritage relating to the sky in the form of sundials, old observatories and the like, are commonly found in many cities in the Old World, but rarely in the New. This paper examines astronomical heritage embodied in the Barolo Palace in Buenos Aires. While references to Dante Alighieri and his poetry are scattered in streets, buildings and monuments around the Western world, in the city of Buenos Aires, the only street carrying Dante's name is less than three blocks long and, appropriately, is a continuation of Virgilio street. A couple of Italian immigrants -a wealthy businessman, Luis Barolo, and an imaginative architect, Mario Palanti- foresaw this situation nearly a century ago, and did not save any efforts or money with the aim of getting Dante and his cosmology an appropriate monumental recognition, in reinforced concrete. The Barolo Palace is a unique combination of both astronomy and the worldview displayed in the Divine Comedy, Dante's poetic masterpiece. It is known that the Palace's design was inspired by the great poet, but the details are not recorded; this paper relies on Dante's text to consider whether it may add to our understanding of the building. Although the links of the Palace's main architectural structure with the three realms of the Comedy have been studied in the past, its unique astronomical flavor has not been sufficiently emphasized. The word of God, as interpreted by the Fathers of the Church in Sacred Scripture, Aristotle's physics and Ptolemy's astronomy, all beautifully converge in Dante's verses, and the Barolo Palace reflects this.

physics.hist-ph↗
arXiv2014

The representations of the sky among the Tomaraho

The Tomárãho is an ethnic group of the Paraguayan Chaco who maintained close contact with nature and developed original ways of explaining and understanding it. This article presents the first results of an interdisciplinary project seeking to provide a detailed analysis of different astronomical elements in the imagined sky of the Tomárãho.

physics.hist-ph↗
arXiv2013

"Science in Tales": Analysis of the images of scientist in young people's fictional literature

In the research field on the "images of scientists" that appear in fictional literature, we focus on a set of tales produced by students of secondary school. Our aim is to connect some traits of the stereotypical scientist that appear in those texts with the traits underlying other cultural productions, since those productions may constitute the probable source of the stereotype. Many common representations of the scientist emerge from an image of science that is inadequate from the point of view of science teaching. It correlates to a lack of interest towards science courses. This lack of interest would contribute to stagnation in the number of students pursuing science and technology careers in Ibero-America in general and especially in Argentina.

physics.pop-ph↗
arXiv2013

The Paraná Ra'anga expedition

Paraná Ra'anga (the image of Paraná, in Guaraní) is the name of a cultural and scientific expedition that traveled the rivers: Río de la Plata, Paraná and Paraguay, from Buenos Aires to Asunción, during March 2010. The project brought together some forty scientists and artists from three countries in a slow and enriching cruise, putting in active contact actors from different backgrounds and disciplines -which usually run separately- in the framework of an unusual space-time experience. The project recovers the historical tradition of the trip as an instrument of knowledge and collaboration between the arts and sciences, necessary to build new ways of seeing and understanding the river and its banks. This article reports on the motivations of this project and its projection.

physics.pop-ph↗
arXiv2013

Diurnal astronomy: using sticks and threads to find our latitude on Earth

It is well known that the length and orientation of a shadow cast by a vertical gnomon depends on the time of the day and on the season of the year. But it also depends on the latitude of the site of observation. During the equinoxes, the temporal sequence of the shadows cast by each of the points that form any object follows a straight line from west to east. A simple construction using sticks and threads can be used to materialize the plane of celestial equator's local projection, giving us a way to calculate our astronomical latitude during daytime with high precision.

physics.pop-ph↗
arXiv2013

The explanation of eclipses in Greco-Roman antiquity

The search of a rational explanation of eclipses pervades the beginnings of philosophical and scientific thought. Within this intellectual frame, the knowledge of the "saros cycle" (a cycle of 18 years, 10 or 11 days and 1/3 of a day that separates two successive sun or moon eclipses of similar features), inherited by the Greeks from the Babylonians, favored important theoretical developments in the West. The purpose of this paper is to present, briefly and schematically, a) the ancient theorizations on the causes of eclipses, b) the range of predictability of eclipses in Antiquity, c) the warnings -transmitted by some classical writers- to those who want to observe in naked eyes a solar eclipse, and d) the popular beliefs and social practices upon the occurrence of unexpected eclipses in ancient times.

physics.hist-ph↗
arXiv2013

A palace for astronomy in Buenos Aires

In no other epoch of Western history like in the Middle Ages, cosmology was so key an element of culture and, one way or another, the motion of the heavens ended up impregnating the literature of that time. Among the most noteworthy poets we find Dante Alighieri, who became famous for his Commedia, a monumental poem written roughly between 1307 and his death in 1321, and which the critics from XVIth century onwards dubbed Divina. In this and other works, Dante pictures the cosmic image for the world, summing up the current trends of Neoplatonic and Islamic traditions. The Barolo Palace in the city of Buenos Aires is a singular combination of both astronomy and the worldview displayed in Dante's poetic masterpiece. Some links of the Palace's main architectural structure with the three realms of the Comedy have been studied in the past. In this note we consider its unique astronomical flavor, an issue which has not been sufficiently emphasized yet.

physics.hist-ph↗
arXiv2012

Anti-positivism, theoretical sciences and relativity in the Argentina of the 1920s

Observing the early years of the 1920's, it is possible to detect a fracture in the perception of relativity theory in Argentina, characterized by the publication of a series of strictly scientific studies on this theory, in parallel with presentations aimed at the general culture. In this work, we attempt to relate this fracture with the advances made by Anti-Positivist ideas in the higher echelons of Argentine culture. The new philosophical approach configured a new vision of science that questioned the traditional methodology of the experimental sciences and attributed to the theoretical sciences a more prominent role than they had in the past. In this work, we present a detailed account of a 1923 paper by José B. Collo and Teófilo Isnardi, two young Argentine physicists trained in Germany, which is a representative contribution to this new trend.

physics.hist-ph↗
arXiv2011

The Tomaraho Conception of the Sky

The small community of the Tomaraho, an ethnic group culturally derived from the Zamucos, became known in the South American and world anthropological scenario in recent times. This group, far from the banks of the Paraguay river, remained concealed from organized modern societies for many years. Like any other groups of people in close contact with nature, the Tomaraho developed a profound and rich world view which parallels other more widely researched aboriginal cultures as well as showing distinctive features of their own. This is also apparent in their imagery of the sky and of the characters that are closely connected with the celestial sphere. This paper is based on the lengthy anthropological studies of G. Sequera. We have recently undertaken a project to carry out a detailed analysis of the different astronomical elements present in the imagined sky of the Tomaraho and other Chamacoco ethnic groups. We will briefly review some aspects of this aboriginal culture: places where they live, regions of influence in the past, their linguistic family, their living habits and how the advancement of civilization affected their culture and survival. We will later mention the fieldwork carried out for decades and some of the existing studies and publications. We will also make a brief description of the methodology of this work and special anthropological practices. Last but not least, we will focus on the Tomaraho conception of the sky as well as describe the research work we have been doing in recent times.

physics.hist-ph↗
arXiv2011

Whither Does the Sun Rove?

If one asked some friends where on the horizon they should expect to see the sunrise, half of the answers would be "in the east". Of course, something analogous would happen with the sunset and the west. However, sunrise and sunset virtually never occur at these cardinal points. In fact, those answers correctly describe observations only during the equinoxes, when either autumn or spring begin. Once we recall this, the next natural question to ask ourselves is: how far from the east (or from the west) the rising (or setting) Sun is located for a given latitude of the observer and for a given day of the year. In this paper we supply some simple tools to easily visualize the angular (southward or northward) departure of the rising and setting Sun on the horizon from the east-west direction in a pictorial way, without the need of mathematics. These tools have proven a valuable resource in teaching introductory physics and astronomy courses.

physics.pop-ph↗
arXiv2010

Investigation carried out with pre-service elementary teachers on some basic astronomical topics

We perform a situational diagnosis in topics of astronomy of pre-service elementary teachers in order to try and develop didactic tools that better collaborate with their formal education. In this work we present the instrument we designed to put in evidence some of the most frequently used models on a few basic astronomical notions endowed by them. We work with an open written questionnaire comprising a limited but representative group of basic astronomical notions. We discuss the results of two first pilot tests, provided to 30 individuals, and we comment on the necessary changes applied to the instrument in order to design the final questionnaire, which was then provided to another group of 51 pre-service elementary teachers. A detailed qualitative analysis of the answers revealed many well-known alternative conceptions, and others that seem new. We find that prospective teachers have a hard time in trying to explain the movements of the Moon and its phases. They also meet difficulties to recognize and explain a couple of astronomical elements that make part of our ordinary language, like the origin of a shooting star and the real identity of the "lucero" (i.e., planet Venus). Amongst the answers offered to explain the causes of the seasons, we found a singular causality, which we think has not been sufficiently emphasized in the literature so far. Many of the inquired people did not advance an explicative model -a cause: say, the tilt of the Earth's axis- to justify a particular phenomenon -the effect: the seasons on the Earth-, but rather made use of another phenomenon/effect, in the present case related to the climate, in order to explain the seasons. However, as we know, this phenomenon/effect (the climate) has a strong astronomical component. We present here the full results of the first two tests and of the final instrument employed, and we draw some conclusions.

physics.ed-ph↗