Who is aristotle astronomy

Whilst thought of as a theoretical philosopher he also conducted experiments in several fields. His works on astronomy and the physics of motion were written in On the heavens and Physics. Like Empedocles before him Aristotle saw all matter on Earth as being composed of combinations of only four elements; earth, air, fire and water with the properties of cool, moist, hot and dry. The stars were made of a separate fifth element, quintessence and were incorruptible and eternal.

Motion in the heavens was natural, unforced and circular so that the planets and Sun orbited a fixed, unmoving spherical Earth in circular orbits. On Earth, however, matter was corruptible and subject to decay. Motion was linear with objects requiring a force acting on them to stay in motion. It is was not until Newton in the second half of the seventeenth century that this concept of forced motion was overthrown.

Aristotle's own model of the Universe was a development of that of Eudoxus who had also studied under Plato. It had a series of 53 concentric, crystalline, transparent spheres rotating on different axes.

Each sphere was centered on a stationary Earth so the model was both geocentric and homocentric. Stars were fixed on the outer sphere. The Moon marked the boundary between the unchanging, constant heavens and the corruptible Earth. According to Aristotelian cosmology it was only within the sub-lunary sphere, that is between the Earth and Moon, that changeable phenomena such as comets could exist.

The last of the great classical astronomers, Claudius Ptolemy lived in Alexandria. He contributed to mathematics, optics, geography and music but is chiefly remembered for his vast work on astronomy, known as the Almagest. In it he detailed a model of the Universe that profoundly influenced Western and Arabic thought for the next 1, years.

Ptolemy relied heavily on tools invented and observations made by earlier astronomers. Apollonius - BC had developed the concepts of the eccentric and the epicycle to explain planetary motions see Figure 1. Hipparchus - BC had organised earlier Babylonian records together with his own observations to develop a catalogue of stars. He plotted them on a celestial sphere and introduced the concept of comparing brightnesses on a magnitude scale that forms the basis of that still used today.

Ptolemy synthesised all this work and incorporated his own careful observations to produce a model that was to become accepted as the standard model until the s. The Ptolemaic model had a spherical, unmoving Earth in the central region of the Universe, its natural place.

Note contrary to common misconception, it was not strictly geocentric as the model used eccentrics; rather it was geostatic. The Sun and the five planets had their motions explained by combinations of epicycles, deferents and eccentrics. In total some seventy circles and spheres were required. Ptolemy's desire, inspired by Plato, that his model should fit observations and save appearances led him to introduce a subtle device, the equant , into his model. Each heavenly body had its own equant, the point around which motions of four epicycles appeared uniform.

The equant did not coincide with the centre of a planet's deferent. Whilst the concept of the equant broke with the precept that the motion of spheres about their centres be uniform it was effective in accounting for the variations noted in the retrograde motion of some planets.

To us Ptolemy's model seems overly complex and clearly wrong yet it survived as the standard model used by scholars for 1, years. Why was this? There are several reasons:. It was not seriously challenged until the mid's by the work of Copernicus.

Skip to main content. Australia Telescope National Facility. Accessibility menu. Interface Adjust the interface to make it easier to use for different conditions. Interface Size. High contrast mode This renders the document in high contrast mode. Aristotle knew that the earth was a sphere. Philosophically, he argues that each part of the earth is trying to be pulled to the center of the earth, and so the earth would naturally take on a spherical shape.

Gravitationally, this is actually accurate! He then points out observations that support the sphericalness of the earth. First, the shadow of the earth on the moon during a lunar eclipse was always circular. The only shape that always casts a circular shadow is a sphere. Second, as one traveled more north or south, the positions of the stars in the sky change. There are constellations visible in the north that one cannot see in the south and vice versa.

He uses this to also argue that the earth isn't very big, because you don't have to travel very far to notice the difference. Third, he says not to discount those who say that Morroco and India are really close to each other, because there are elephants in both of these regions. Aristotle talks about the work of Eudoxus and Callippus, who had developed an earth centered model of the planets. In these models, the center of the earth is the center of all the other motions. While it is not sure if Eudoxus and Callippus actually thought the planets moved in circles, Aristotle certainly does.

Aristotle even adds "counteracting spheres" so that the motion of one sphere doesn't interfere with the motion of the one next to it. The purpose of he epicycle was to account for retrograde motion , where planets in the sky appear to be slowing down, moving backwards, and then moving forward again.

Unfortunately, these explanations did not account for all the observed behaviors of the planets. While this system remained the accepted cosmological model within the Roman, Medieval European and Islamic worlds for over a thousand years, it was unwieldy by modern standards. However, it did manage to predict planetary motions with a fair degree of accuracy, and was used to prepare astrological and astronomical charts for the next years.

By the 16th century, this model was gradually superseded by the heliocentric model of the universe, as espoused by Copernicus, and then Galileo and Kepler. Credit: Public Domain. In the 16th century, Nicolaus Copernicus began devising his version of the heliocentric model. Like others before him, Copernicus built on the work of Greek astronomer Atistarchus, as well as paying homage to the Maragha school and several notable philosophers from the Islamic world see below.

By , Copernicus began circulating copies amongst his friends, many of whom were fellow astronomers and scholars. This forty-page manuscript described his ideas about the heliocentric hypothesis, which was based on seven general principles. These principles stated that:. Thereafter he continued gathering data for a more detailed work, and by , he had come close to completing the manuscript of his magnum opus — De revolutionibus orbium coelestium On the Revolutions of the Heavenly Spheres.

In it, he advanced his seven major arguments, but in more detailed form and with detailed computations to back them up. A comparison of the geocentric and heliocentric models of the universe. Credit: history.

By placing the orbits of Mercury and Venus between the Earth and the Sun, Copernicus was able to account for changes in their appearances. In short, when they are on the far side of the Sun, relative to Earth, they appear smaller but full. It also explained the retrograde motion of planets like Mars and Jupiter by showing that Earth astronomers do not have a fixed frame of reference but a moving one.

This further explained how Mars and Jupiter could appear significantly larger at certain times than at others. In essence, they are significantly closer to Earth when at opposition than when they are at conjunction. However, due to fears that the publication of his theories would lead to condemnation from the church as well as, perhaps, worries that his theory presented some scientific flaws he withheld his research until a year before he died.

It was only in , when he was near death, that he sent his treatise to Nuremberg to be published. As already noted, Copernicus was not the first to advocate a heliocentric view of the Universe, and his model was based on the work of several previous astronomers. The first recorded examples of this are traced to classical antiquity, when Aristarchus of Samos ca. Credit: Wikipedia Commons. In his treatise The Sand Reckoner , Archimedes described another work by Aristarchus in which he advanced an alternative hypothesis of the heliocentric model.

As he explained:. This is the common account… as you have heard from astronomers. But Aristarchus of Samos brought out a book consisting of some hypotheses, in which the premises lead to the result that the universe is many times greater than that now so called. His hypotheses are that the fixed stars and the sun remain unmoved, that the earth revolves about the sun in the circumference of a circle, the sun lying in the middle of the orbit, and that the sphere of the fixed stars, situated about the same center as the sun, is so great that the circle in which he supposes the earth to revolve bears such a proportion to the distance of the fixed stars as the center of the sphere bears to its surface.

According to Archimedes, Aristarchus claimed that the stars were much farther away than commonly believed, and this was the reason for no discernible parallax. A Hellenistic astronomer who lived in the Near-Eastern Seleucid empire, Seleucus was a proponent of the heliocentric system of Aristarchus, and is said to have proved the heliocentric theory.

According to contemporary sources, Seleucus may have done this by determining the constants of the geocentric model and applying them to a heliocentric theory, as well as computing planetary positions possibly using trigonometric methods.

In the 5th century CE, Roman philosopher Martianus Capella of Carthage expressed an opinion that the planets Venus and Mercury revolved around the Sun, as a way of explaining the discrepancies in their appearances. Indian astronomers and cosmologists also hinted at the possibility of a heliocentric universe during late antiquity and the Middle Ages.

In CE, Indian astronomer Aaryabhata published his magnum opus Aryabhatiya , in which he proposed a model where the Earth was spinning on its axis and the periods of the planets were given with respect to the Sun. He also accurately calculated the periods of the planets, times of the solar and lunar eclipses, and the motion of the Moon.

In it, he developed a computational system for a partially heliocentric planetary model, in which the planets orbit the Sun, which in turn orbits the Earth.

Also, the heliocentric model of the universe had proponents in the medieval Islamic world, many of whom would go on to inspire Copernicus. Prior to the 10th century, the Ptolemaic model of the universe was the accepted standard to astronomers in the West and Central Asia. However, in time, manuscripts began to appear that questioned several of its precepts. In the early 11th century, Egyptian-Arab astronomer Alhazen wrote a critique entitled Doubts on Ptolemy ca. Around the same time, Iranian philosopher Abu Rayhan Biruni — discussed the possibility of Earth rotating about its own axis and around the Sun — though he considered this a philosophical issue and not a mathematical one.

At the Maragha and the Ulugh Beg aka. Over time, many religious scholars tried to argue against his model. German mathematician and astronomer Johannes Kepler also helped to refine the heliocentric model with his introduction of elliptical orbits.

Prior to this, the heliocentric model still made use of circular orbits, which did not explain why planets orbited the Sun at different speeds at different times. Whereas previous ideas of motion depended on an outside force to instigate and maintain it i. Although its progress was slow, the heliocentric model eventually replaced the geocentric model. In the end, the impact of its introduction was nothing short of a revolutionary. We have written many interesting articles on the heliocentric model here at Universe Today.

For more information on heliocentrism, take a look at these articles from NASA on Copernicus or the center of the galaxy. And along the way, many names stand out as examples of people who achieved breakthroughs and helped lay the foundations of our modern understanding. There has also been significant controversy — particularly in Germany during the 19th century — over whether or not Democritus deserves credit for atomic theory.

This argument is based on the relationship Democritus had with contemporary philosopher Leucippus, who is renowned for sharing his theory about atoms with him. However, their theories came down to a different basis, a distinction that allows Democritus to be given credit for a theory that would go on to become a staple of the modern scientific tradition. Democritus, by Hendrik ter Brugghen — Heraclitus, Credit: rijksmuseum.

The precise date and location of Democritus birth is the subject the debate. However, other sources claim he was born in Miletus, a coastal city of ancient Anatolia and modern-day Turkey, and that he was born in BCE.

It is further argued that as a reward for his service, the Persian monarch gave his father and other Abderites gifts, and left several Magi among them. Democritus was apparently instructed by these Magi in astronomy and theology. After his father had died, Democritus used his inheritance to finance a series of travels to distant countries.

Desiring to feed his thirst for knowledge, Democritus traveled extensively across the known world, traveling to Asia, Egypt and according to some sources venturing as far as India and Ethiopia. His writings include descriptions of the the cities of Babylon and Meroe in modern-day Sudan. Upon returning to his native land, he occupied himself with the study of natural philosophy. His wealth allowed him to purchase their writings, and he wrote of them in his own works.

In time, he would become one of the most famous of the pre-Socratic philosophers.