Astronomer, Mathematician, Philosopher, Geographer, Inventor (c.190 BC – c.120 BC)

The greatest astronomer who ever lived. His massive work spans the fields of astronomy, mathematics, geography and philosophy, all of which contributed enormously to the revival of the sciences during the Renaissance as well as the development of modern technology.

He wrote numerous books, most of which were lost during the fire of the library of Alexandria. Fortunately, excerpts from some of his most important works were included in Ptolemy’s “Almagest” and were enough to know his work as well as to acknowledge him as one of the greatest geniuses of all time. Other scientists, such as Strabo, Pliny and Plutarch also saved some excerpts.

Hipparchus used many different instruments in astronomy, most important of which were the *astrolabe*, the *plinthis* and the *quadrant*. With the *astrolabe* he was able to make precise measurements on the coordinates of the asterisms, as well as discover the equinoctial precession, which is considered as the third most important motion of our planet, after the one around the sun and around its own axis. The *plinthis* was a simple astronomical instrument suitable to calculate the latitude of a place while the quadrant was a sophisticated instrument used in astronomy and navigation for the calculation of astronomical sizes. It was also used in topography and construction for the measurement of terrestrial distances. In addition, it could be used at any given hour of the day as a locator of place and as a sundial. Other instruments were the *epipedosphairos*, with which he could make stereographic projection, which he also discovered using the device and the dioptre, with which he was able to calculate precisely the distance between the sun and the moon. He also attempted to measure the size of the sun and the moon, but his instruments at the time were imperfect. Other instruments include the *heliorologion*, *heliotropion*, the hourglass, the solid sphere, the *hydrologion* and many more.

Hipparchus is the father of trigonometry, a branch in mathematics that deals with the relationships of angles and triangles. Even though spherical trigonometry was already known and used by Apollonius of Perga before him, Hipparchus used this to calculate spherical triangles in order to solve various astronomical problems. He was the first to perform the stereographic projection of the sphere. Hipparchus was interested in meteorology and used his mathematical knowledge to establish some empirical prognostics which he used to predict the weather. In geography, he proved that the geographic latitude of a place is equal to the height of the polar star from the horizon of that place and that the geographic longitude of two places is equal to the difference of time between the two places. He created geographical maps based on mathematical calculations which advanced the science of chartography.

Hipparchus’ major field of interest was astronomy. One day, while he was gazing at the sky, he noticed a bright star which he had not seen before. Since he knew all the stars in the sky, he realized that it was a new star, the first “new” star ever recorded in astronomic literature. Then, Hipparchus made a decision, according to Pliny “*to undertake a work before which even God will retreat*”. He decided to make a catalogue of all the stars of the sky, providing them with their exact spot and brightness in such a way that future astronomers would know whether the stars they observed were new or existed thousands of years ago. Thus, Hipparchus introduced the fundamental notion in astronomy that “stars are not eternal in the sky”.

Hipparchus’ chart contained 1080 stars with their exact coordinates. Timochares, another astronomer had made a similar chart 166 years before him. Hipparchus compared his chart with that of his predecessor and concluded that the stars had shifted their position by two degrees. This is how he managed to discover and measure the equinoctial precession or axial precession, one of the greatest discoveries in the history of astronomy. Hipparchus calculated that the Earth completed a precessional rotation around its axis every 26.000 years. Furthermore, he calculated with exact precision the duration of the year, the duration of the months, the obliquity of the ecliptic, numerous measurements concerning the moon’s orbit, calculated the Earth’s longest cycle with extraordinary accuracy and precision, created models for the motion of the sun and the moon, discovered important aspects of the planetary orbits and many other discoveries.

Hipparchus is recognized worldwide as the father of scientific astronomy and trigonometry. His immense success was based on his brilliant observation of the star sky, followed by their calculation and then drawing conclusions based on his observations. His observations and his discoveries are still used today in a myriad of sciences, from engineering and navigation, to game development and crystallography.

Bibliography

- Georgakopoulos, Konstantinos.
*Ancient Greek Scientists*. Georgiades: Athens, 1995. Print. - ”Hipparchus”.
*Helios New Encyclopaedic Dictionary*. Passas, I. Athens. 1946. Print. - Kotsanas, Kostas.
*Ancient Greek Technology: The Inventions of the Ancient Greeks.*Pyrgos: Kostas Kotsanas, 2013. Print. - The Editors of Encyclopaedia Britannica.”Hipparchus.”
*Encyclopaedia Britannica.*Web. 4 Feb, 2011.

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