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Ptolemy presented his astronomical models in convenient tables, which could be used to compute the future or past position of the planets. The Almagest also contains a star catalogue, which is a version of a catalogue created by Hipparchus. Its list of forty-eight constellations is ancestral to the modern system of constellations, but unlike the modern system they did not cover the whole sky (only the sky Hipparchus could see).

Ptolemy, however, 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' parameters were adopted independently of observations

Early Baroque artist's rendition

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Replica of Newton's second Reflecting telescope that he presented to the Royal Society in 1672

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Illustration of a dispersive prism decomposing white light into the colours of the spectrum, as discovered by Newton

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Newton also built the first practical reflecting telescope and developed a theory of colour based on the observation that a prism decomposes white light into the many colours of the visible spectrum. He formulated an empirical law of cooling, studied the speed of sound, and introduced the notion of a Newtonian fluid.

Newton's Principia formulated the laws of motion and universal gravitation, which dominated scientists' view of the physical universe for the next three centuries. By deriving Kepler's laws of planetary motion from his mathematical description of gravity, and then using the same principles to account for the trajectories of comets, the tides, the precession of the equinoxes, and other phenomena, Newton removed the last doubts about the validity of the heliocentric model of the cosmos. This work also demonstrated that the motion of objects on Earth and of celestial bodies could be described by the same principles. His prediction that the Earth should be shaped as an oblate spheroid was later vindicated by the measurements of Maupertuis, La Condamine, and others,

Godfrey Kneller's 1689 portrait of Isaac Newton (age 46)

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THE SUPERNOVA OF 1604 Remnant of Kepler's Supernova SN 1604 In October 1604, a bright new evening star (SN 1604) appeared, but Kepler did not believe the rumors until he saw it himself. Kepler began systematically observing the nova. Astrologically, the end of 1603 marked the beginning of a fiery trigon, the start of the ca. 800-year cycle of great conjunctions; astrologers associated the two previous such periods with the rise of Charlemagne (ca. 800 years earlier) and the birth of Christ (ca. 1600 years earlier), and thus expected events of great portent, especially regarding the emperor.

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THE ALMAGEST

The Almagest is a 2nd-century mathematical and astronomical treatise on the apparent motions of the stars and planetary paths. Written in Greek by Claudius Ptolemy, a Roman era scholar of Egypt, it is one of the most influential scientific texts of all time, with its geocentric model accepted for more than twelve hundred years from its origin in Hellenistic Alexandria, in the medieval Byzantine and Islamic worlds, and in Western Europe through the Middle Ages and early Renaissance until Copernicus.

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Once Kepler had corrected the Almagest model, he compared its predictions with his observational data. In particular, Kepler investigated the apparent motion of Mars in the night sky. Kepler found that his model performed extremely well, but that there remained small differences between its predictions and the observational data. The maximum discrepancy was about 8': i.e., about 1/4 the apparent size of the sun. By the standards of naked-eye astronomy, this was a very small discrepancy indeed.
Although Kepler adopted the heliocentric approach of Copernicus, what he effectively first did was to perfect Ptolemy's model of the solar system (or, rather, its heliocentric equivalent)

A 1610 portrait of Johannes Kepler by an unknown artist

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THE PRIMUM MOBILE
In classical, medieval and Renaissance astronomy, the Primum Mobile, or "first moved," was the outermost moving sphere in the geocentric model of the universe. The concept was introduced by Ptolemy to account for the apparent daily movement of the heavens around the Earth, producing the east-to-west rising and setting of the sun and stars, and reached Western Europe via Avicenna.

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NICOLAUS COPERNICUS

In 1543, twenty-eight years before Kepler's birth, Copernicus published the landmark astronomical text De Revolutionibus, or On the Revolutions of the Heavenly Spheres. The standard story about Copernicus's achievement is that by the sixteenth century, the Ptolemaic system had gotten too complicated and inaccurate to bear. In a stroke of genius, Copernicus moved the sun to the center of the universe creating a new system of brilliant simplicity and inarguable accuracy. Despite the attempts of the Catholic Church to drown out Copernican arguments, Ptolemy's system was soon overthrown. The Copernican system is thus heralded as a prime example of the triumph of a new, modern scientific era. The story is true only in part. Copernicus did revolutionize astronomy by introducing a heliocentric system. But the concept of a sun-centered universe was not brand new and, in fact, had occurred to many of the ancient philosophers.

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Johannes Kepler Johannes Kepler 1610

A 1610 portrait of Johannes Kepler by an unknown artist

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THE PRIMUM MOBILE

In classical, medieval and Renaissance astronomy, the Primum Mobile, or "first moved," was the outermost moving sphere in the geocentric model of the universe.The concept was introduced by Ptolemy to account for the apparent daily movement of the heavens around the Earth, producing the east-to-west rising and setting of the sun and stars, and reached Western Europe via Avicenna.

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The Ptolemaic/Geocentric order of spheres from Earth outward is: Moon Mercury Venus Sun Mars Jupiter Saturn Fixed Stars Primum Mobile (First Moved).

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An illustration of the Ptolemaic geocentric system by Portuguese cosmographer and cartographer Bartolomeu Velho, 1568 (Bibliothèque Nationale, Paris

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A way to remember the planets in the heliocentric model and in order is

My = Mercury

Very = Venus

Elderly = Earth

Mother = Mars

Just = Jupiter

Served = Saturn

Us = Uranus

Nachos = Neptune

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Galileo, was an Italian physicist, mathematician, engineer, astronomer, and philosopher who played a major role in the scientific revolution. His achievements include improvements to the telescope and consequent astronomical observations and support for Copernicanism. Galileo has been called the "father of modern observational astronomy", the "father of modern physics", the "father of science"and "the father of modern science"

He met with opposition from astronomers, who doubted heliocentrism due to the absence of an observed stellar parallax. The matter was investigated by the Roman Inquisition in 1615, which concluded that heliocentrism was false and contrary to scripture, placing works advocating the Copernican system on the index of banned books and forbidding Galileo from advocating heliocentrism

Galileo was also well known because his contributions to observational astronomy include the telescopic confirmation of the phases of Venus, the discovery of the four largest satellites of Jupiter (named the Galilean moons in his honour), and the observation and analysis of sunspots. Galileo also worked in applied science and technology, inventing an improved military compass and other instruments.

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more information about mercury

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Galileo watching the night sky through his telescope

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This drawing from an Icelandic manuscript dated around 1750 illustrates the geocentric model

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a greek calculation about the size of the sun, earth and moon

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solar system example

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The geocentric model was developed thousands of years ago by Greek philosophers and was the accepted model of the Solar System for centuries. Geocentric actually means earth centered. This model is also called the Ptolemaic system in honour of the Greek scientist and philosopher Claudius Ptolemy, although the theory was around years before him. The geocentric model places the Earth at the center of the universe with the Sun, Moon, stars, and planets circling it.