Isaac Newton

Sir Isaac Newton was an English physicist, mathematician, astronomer, natural philosopher, alchemist and theologian. He is known and considered by many scholars and members of the public to be one of the most influential people in human history. He lived from January 4^th 1643- March 31^st 1727. Isaac Newton’s book, Philosophice Naturalis Principia Mathematica (which was Latin for Mathematical Principles Of Natural Philosophy) was published in 1687 and is known to be one of the most important scientific books ever written in history. In his book, he describes universal gravitation and the three laws of motion which is all very relevant. It dominated the scientific view of the physical universe itself for the next three centuries. He also showed that the motions of objects on Earth and of celestial bodies are governed by the same set of natural laws. He did this by demonstrating the consistency between Kepler’s laws of planetary motion and his theory of gravitation. This itself removed the last doubts of heliocentrism and advancing the Scientific Revolution. Newton built the first practical reflecting telescope and developed his own theory on colour based on the looks that a prism decomposes white light into many colours that from the visible spectrum. He also studied the speed of sound. In mathematics, he is very much known for demonstrating the generalized binomial theorem, developed Newton’s method for approximating the roots of a function, and contributed to the study of power series.

Johannes Kepler

Johannes Kepler was a German mathematician, astronomer and astrologer and generally a key figure in the 17^th century scientific revolution. He is best known and is for famous for his eponymous laws of planetary motion which was codified by later astronombers basked on his works Astronomia nova, Harmonices Mundi and Epitome of Copernican Astronomy. All these works also provided one of the foundations for Isaac Newton’s theory of universal gravitation. He lived from December 27^th 1571- November 15^th 1630.
In the era Kepler lived in, there was no clear distinction between astronomy and astrology but there was a very strong division between astronomy and physics. He had also been known to incorporate religious arguments and reasoning into his work. He was motivated by the religious conviction that God had created the world according to an intelligible plan that is accessible through the natural light of reason. This new astronomy he had made was named “celestial physics.”

Kepler contributed a mathematical law of motion to astronomy which were three laws. These three laws were as followed:
1. The orbit of every planet is an ellipse with the sun at one of the foci. An ellipse is characterized by its two focal points; see illustration. Thus, Kepler rejected the ancient Aristotelean and Ptolemaic and Copernican belief in circular motion.

2. A line joining a planet and the sun sweeps out equal areas during equal intervals of time as the planet travels along its orbit. This means that the planet travels faster while close to the sun and slows down when it is farther from the sun. With his law, Kepler destroyed the Aristotelean astronomical theory that planets have uniform velocity.

3. The squares of the orbital periods of planets are directly proportional to the cubes of the semi-major axes (the "half-length" of the ellipse) of their orbits. This means not only that larger orbits have longer periods, but also that the speed of a planet in a larger orbit is lower than in a smaller orbit.

These three laws are crucially important to astronomy and mathematics law of motion.

Tycho Brahe

Tycho Brahe was a Danish nobleman known for his accuracy and comprehensiveness in astronomy and planetary observations. He was well known for being an astronomer and alchemist. He lived from December 14^th 1546 – October 24^th 1601. He destroyed the popular theory of the celestial spheres with precision measurements that had shown the celestial heavens were not immutable as previously assumed by Aristotle and Ptolemy in his De nova stella of 1573. Using similar measurements he showed that comets were also not atmospheric phenomena, as previously thought, and must pass through the celestial spheres. His Danish name is  “Tyge Ottesen Brahe” and he had adopted the Latinized name “Tycho Brahe” at around age fifteen, and he is now generally referred to as “Tycho.” After a number of disagreements with the new Fanish king in 1597, he was invited personally by the Bohemian king and the Holy Roman emperor Rudolph II to Prague, which is when and where he became the official imperial astronomer. He at this time built the new observatory. Here, from 1600 until his death in 1601, he was assisted by Kepler. Kepler later used Tycho's astronomical results to develop his own theories of astronomy. As an astronomer, Tycho worked to combine what he saw as the geometrical benefits of the Copernican System with the philosophical benefits of the Ptolemaic System into his own model of the universe, the Tychonic System. Tycho is known to have the most accurate astronomical observations of his time, and the data were used by his assistant, Kepler, to derive the laws of planetary motion. No one before Tycho had attempted to make so many planetary observations and he is now very well respected for it.

Galileo

Galileo Galilei was an Italian physicist, mathematician, astronomer and philosopher who played a major role in the Scientific Revolution. He had made many achievements throughout his career, most important he had made improvements to the telescope and consequent astronomical observations and overall support for Copernicanism. Galileo has been named many things like the “father of modern observational astronomy,” the “father of modern physics”, the “father of modern science” and so on. He lived from Feb 15^th 1564- January 8^th 1642. His contributions to observational astronomy include the telescopic confirmation of the phases of Venus, the discovery of the four largest satellites of Jupiter and the observation and analysis of sunspots. He had also worked in many other areas including science and technology, inventing an improved military compass. Throughout his lifetime, there was much controversy around his championing of Copernicanism when a large majority of philosophers and astronomers still believed the thought that the Earth is at the center of the universe. After 1610 he began publicly stating and supporting the heliocentric view which had placed the Sun at the center of the universe, he met with philosophers disagreeing bitterly and two of the latter eventually denounced him to the Roman Inquisition early in 1615. In February 1616, although he had been cleared of any offence, the Catholic Church nevertheless condemned heliocentrism as "false and contrary to Scripture", and Galileo was warned to abandon his support for it which he had promised to do so. He later then defended his views in his most famous work, Dialogue Concerning the Two Chief World Systems, which was published in 1632, he was tried by the Inquisition and found to be suspected of heresy. This forced him to recant and he spent the rest of his life under house arrest.

Copernicus

Nicolaus Copernicus was a Renaissance astronomer, priest and the first person ever to formulate a comprehensive cosmology that displaced the Earth from the center of the universe. He lived from Feb. 19^th 1473- May 24^th 1543. Copernicus’ wrote a book that was published just before his dead in 1543. His epochal book, De revolutionibus orbium coelestium, is generally regarded as the starting point of modern astronomy and the defining epiphany that began the scientific revolution. It asserted that the earth rotated on it’s axis once daily and traveled around the sun once yearly: a fantastic concept for the times. He also made the heliocentric model which had the Sun at the center of the universe, and it demonstrated that the observed motions of celestial objects can be explained without putting Earth at rest in the center of the universe. He is now a landmark in the history of science and it is often referred to as the ‘Copernican Revolution.’

Ptolemy

Ptolemy, known as Claudius Ptolemaeus in Greek, was a mathematician, astronomer, geographer, and astrologer. He lived in Egypt under Roman rule and was believed to had been born in the town of Ptolemais Hermiou in the Thebaid. He lived from AD 90- 168. He was the author of several scientific treatises, the first which was the astronomical treatise now known as the Almagest. The second is the Geography, which is a thorough discussion of the geographic knowledge of the Greco-Roman world. The third is the astrological treatise known sometimes in Greek as the Apotelesmatika more commonly in Greek as the Tetrabiblos. Ptolemy claimed to have derived his geometrical models from selected astronomical observations by his predecessors spanning more than 800 years, though astronomers have for centuries suspected that his models’ parameterse were adopted independently of observations. The astronomical model that Ptolemy presented was shown in convenient tables which were used to compute the future or past position of the planets. Ptolemy’s model was geocentric and was almost universally accepted until the appearance of simpler heliocentric models during the scientific revolution. He estimated the Sun was at an average distance of 1210 Earth radii while the radius of the sphere of the fixed stars was 20,000 times the radius of the Earth. He also presented a tool that was quite useful for astronomical calculations in his Handy Tables, which tabulated all the data needed to compute the positions of the Sun, Moon, and planets, the rising and the setting of the stars, and eclipses of the Sun and Moon. In the Phaseies (Risings of the Fixed Stars) Ptolemy gave a parapegma, a star calendar or almanac based on the hands and disappearances of stars over the course of the solar year.

Hipparchos

Hipparchos was a Greek astrologer, astronomer, geographer and mathematician of the Hellenistic period. He is well known for being the founder of trigonometry. Hipparchos was born in Nicea and probably died on the island of Rhodes. As far as it’s known, he was known to have been a working astronomer at least from 147 to 127 BC. He is considered the greatest ancient astronomical observer and, by some, the greatest overall astronomer of antiquity. He is also well known for being the first whose quantitative and accurate models for the motion of the Sun and Moon survive. With his solar and lunar theories and his trigonometry, he may have been the first to develop a reliable method to predict solar eclipses. His other reputed achievements include the discovery of Earth's precession, the compilation of the first comprehensive star catalog of the western world, and possibly the invention of the astrolabe also of the armillary sphere which he used during the creation of much of the star catalogue. He was a huge impact on astronomy.

Aristotle

Aristotle was a Greek philosopher who believed that celestial bodies are spheres. Aristotle used several methods to prove that the Earth is a sphere. One was the observation that during a lunar eclipse, the Earth's shadow on the Moon is always a circle. Also, upon seeing the Moon pass in front of Mars, Aristotle concluded that Mars is higher up in the heavens than the Moon. He developed many physical works which had a bearing on the study of astronomy, including the physics which explained change, motion, void and time. Aristotle was born in Stagira in Thrace and studied in Athens, where he became a distinguished member of the Academy founded by Plato. While there, he opened a school at Assos. At this time he regarded himself as a Platonist, but his subsequent thought led him further from the traditions that had formed his early background and he was later critical of Plato. In about 344 BC he moved to Mytilene in Lesvos, and devoted the next two years to the study of natural history. Meanwhile, during his residence at Assos, he had married Pythias, niece and adopted daughter of Hermeias, ruler of Atarneus. His major writings on astronomy are brought together in the four-volume Peri ouranou/On the Heavens. Aristotle rejected the notion of infinity and the notion of a vacuum. A vacuum he held to be impossible because an object moving in it would meet no resistance and would therefore attain infinite velocity. Space could not be infinite, because in Aristotle's view, the universe consisted of a series of concentric spheres which rotated around the centrally placed, stationary Earth. If the outermost sphere were an infinite distance from the Earth, it would be unable to complete its rotation within a finite period of time, in particular within the 24-hour period in which the stars, fixed, as Aristotle believed, to the sphere, rotated around the Earth. Aristotle's work in astronomy also included proving that the Earth was spherical. He observed that the Earth cast a circular shadow on the Moon during an eclipse and he pointed out that as one travelled north or south, the stars changed their positions. Aristotle overestimated the Earth's diameter by only 50%.

Eratosthenes

Eratosthenes was a Greek scientist who lived from 276 to 194 B.C. and studied astronomy, geography and math. He is famous for making the first good measurement of the size of the Earth. He was born in Cyrene which is in the modern-day country of Libya.  Eratosthenes is most famous for making the first accurate and good measurement of the size of Earth sometime around 240 B.C. He was also aware that there was no shadow at the bottom of a well in the town of Syene on the summer solstice which meant that the Sun must be straight overhead of Syene on that day. He measured the length of the shadow of a tall tower in Alexandria on the same day. He was hugely important and also gave us a formula for calculating prime numbers, he invented latitude and longitude, and calculated the circumference of the Earth and the distance of the Sun from the Earth. He was only approx. 1% off. He has also been known for creating a map of the earth based on the knowledge available at the time. He was very highly respected, and his calculations of the earth's circumference were used for hundreds of years. Today, his method for finding prime numbers from 1-100 is known as the 'Sieve of Eratosthenes' and is taught in math textbooks.

Pythagoras

Pythagoras was a Greek astronomer and mathematician, born in 572 B.C., in Greece. He believed that everything was related to mathematics and that through mathematics everything could be predicted and measured in rhythmic patterns or cycles. Out of his four mathematical arts, he placed astronomy as one of them and the others being arithmetic, geometry and music. Pythagoras is most known for his theorem, known as the ‘Pythagorean Theorem.’ The Pythagorean Theorem is that ‘'The square of the hypotenuse of a right-angled triangle is equal to the sum of the squares on the other two sides.’ More simply put, a²+b²=c². Pythagoras believed  in the ‘harmony of spheres’ which meant that the planets and stars moved according to mathematical equations, which corresponded to musical notes and thus produced a symphony. Pythagoras was also one of the first to think that the Earth was round, a theory that was finally proved around 330BC by Aristotle. He was sure that the Earth and each of the other bodies in the Universe was a sphere and that they all revolved about one central body. Pythagoras did not take the Sun as a central position, but he imagined an area of central fire. Around this there revolved ten bodies: the Sun, the Earth, the Moon, the five planets which were known at that time, heaven with its stars and a newcomer named Antichthon or "the counter-Earth". Pythagoras had a very strong impact on Astronomy and it’s history.