Hipparchus of Nicaea, Thinker of Geographical Thought

According to NEP 2020, the syllabus has been changed at the university level. New content has been added. Several changes are also noticeable in the subject of geography. The syllabus of the subject of development of geographical thought has also been updated, it has got a touch of modernity. According to the syllabus, the books required for the development of geographical thought are almost insufficient. In an attempt to overcome this predicament, our smallest attempt to develop geographical thought is the post named Hipparchus of Nicaea, Thinker of Geographical Thought.

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Hipparchus of Nicaea, Thinker of Geographical Thought

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Hipparchus of Nicaea: One of the Greek scholars who expanded the scope of geographical knowledge after Eratosthenes and from the middle to the last stage of the Hellenistic period (323-30 BC) was: Hipparchus. Hipparchus was a Greek mathematician and astronomer who followed Eratosthenes. He was born in 190 BC in the city of Nicaea in Bithynia, in the northwestern Anatolia region of ancient Greece; [now called Iznik and located on the eastern shore of Lake Iznik in Turkey in northwestern Asia Minor] but he spent most of his life in Rhodes, where he is known to have made astronomical observations from 161 to 126 BC. Information about his personal life is limited, but a synthesis of later writers suggests that he died in Rhodes around 120 BC, at the age of about 70.
Hipparchus was a Greek thinker of the next generation as Eratosthenes, born six years after Eratosthenes’ death, and the first known critic of Eratosthenes’ geographical ideas. He was the leading astronomer of his time, but had not Ptolemy described his work in his works, he would have remained unknown to us forever. No contemporary works based on his work can be found. In this context, Gerald James Toomer in his book in 1980 mentioned “This was due to the fact that, although Hipparchus gained a great reputation in antiquity, his work was not widely read outside the circle of specialists, probably because they were generally in the form of not very long monographs concerning very different subjects and often his works are very technical.”.

Hipparchus of Nicaea and Greek Geography: As an astronomer, Hipparchus was particularly interested in celestial cartography and his only surviving work on this subject is: “The Commentary on Eudoxus’s and Aratus’s Phaenomena”. The book was first published in Greek by Piero Vettori in Florence in 1567. Later, it was first published in Latin by Denis Pétau in Paris in 1630. The contributions of Hipparchus to Greek geographical thought, based on the works of Strabo, Ptolemy, Tomer, etc., are as follows:

i. Status as Astronomer: Tomer confirms Hipparchus as the greatest astronomical observer of antiquity and arguably the most important astronomer of the ancient world, whose work provided the essential basis for Ptolemy’s “Almagest”. He compiled the first comprehensive star catalogue in the Western world, which recorded about 850 stars; on which the current stellar magnitude system (ranking stars 1-6 based on brightness) was developed. Hipparchus’ “Commentary” can be divided into three parts, in the first part of which Hipparchus presents a qualitative description of the stars of Aretas and their relative positions, along with numerous quantitative problems. In the second part, Hipparchus gives his own precise data for the rising and setting of the first and last stars in each of the 42 constellations, and also indicates the degrees of eclipse on the horizon and meridian at the times of their rising and setting. In the third part, Hipparchus divides the celestial sphere into 24 equinoctial hours and states that, starting from the summer solstice, certain stars are separated by one or very close equinoctial hours. That is, he gives the concept of a 24-hour period in the first day.

ii. Hipparchus’ Coordinate System: Hipparchus’ work on latitude and longitude is an important milestone in the history of geography. In Hipparchus’s lost work “Against the Geography of Eratosthenes”, Hipparchus criticizes the internal contradictions in his predecessor Eratosthenes’ maps and emphasizes the importance of mapping based on astronomical measurements and triangulation. Where Eratosthenes proposed a simple grid, Hipparchus developed the concept of “κλίματα” (Klímata) or parallel circles of latitude based on the length of the longest day (the angle of the sun at the solstice). Hipparchus formalized the use of latitude to determine positions on the Earth’s surface, establishing the “Grade grid”. He overcame the weaknesses of his predecessors and identified several key latitudes, including the equator (0° latitude), the Tropic of Cancer (23.5° north latitude), the Tropic of Capricorn (23.5° south latitude), the Arctic Circle (66.5° south latitude), and the Antarctic Circle (66.5° south latitude). Hipparchus proposed calculating the difference in longitude between places by observing simultaneous lunar eclipses. He recognized that since an eclipse can occur at different places at the same absolute moment, the difference in local time between two observers translates into a difference in longitude. That is, he realized that it was ideal to calculate the difference in longitude between two places by observing lunar eclipses occurring at the same moment everywhere on Earth. He used a meridian passing through Alexandria as a reference point for longitude. He also pioneered the use of the 360-degree circle for measuring geographical positions. He believed that maps should be based solely on astronomical observations and mathematical calculations (trigonometry), not on the unreliable itineraries of sailors. He invented or improved instruments such as the astrolabe and diopter, which divided the circle into 360° for measuring geographical positions, which allowed for more precise measurements of astronomical angles. Hipparchus’ work on latitude and longitude laid the foundation for later geographers. His “Against the Geography of Eratosthenes” paved the way for later geographers such as Claudius Ptolemy to create mathematically rigorous and coordinate-based world maps.

iii. Concept of Climate Zones: Hipparchus introduced the concept of climatology based on latitude. He classified climates into zones based on latitude and was the first to use the term “κλίματα” (Klímata). He proposed a Torrid Zone based on latitude: a zone with high temperatures and abundant sunlight near the equator (0° latitude); two Temperate Zones: a zone between the tropics and the polar circles (23.5° – 66.5° latitude), with moderate temperatures and seasonal changes; and two Frigid Zones: a zone with cold temperatures and limited sunlight near the poles (66.5° – 90° latitude). Hipparchus included the value of the angle of incidence of sunlight, which varied with latitude, based on astronomical observations, in his classification of climate zones. He recognized that the distribution of heat and climate patterns was closely related to the Earth’s rotation and the position of the Sun in the sky. Hipparchus of Nicaea: 

iv. Map Projections: Hipparchus was indeed an important figure in the history of cartography in bridging the gap between spherical astronomy and flat map making through mathematical approximations. Hipparchus made important contributions to map projections by inventing a method of representing the curve of the Earth on flat maps. Hipparchus’ primary innovation was to convert a three-dimensional sphere into a two-dimensional plane using explicit mathematical principles rather than a purely artistic or descriptive method. Hipparchus is credited with creating the earliest map projections such as the stereographic projection and the orthographic projection. Stereographic projection is a method of representing the surface of the Earth on a plane while preserving angles and size. Hipparchus was the first person to use and probably invented stereographic projection. This method projects the sphere onto a tangent plane from one pole to the opposite pole. Orthographic projection refers to a projection system that represents the Earth as seen from a distant point, where the Earth’s surface is presented on a plane. Ptolemy acknowledged Hipparchus’ contributions to map projections and cartography in his Geography, highlighting his importance in the development of these fields. Hipparchus of Nicaea Hipparchus of Nicaea

v. Solar and Lunar Theories: Hipparchus, through his solar and lunar theories, was the first person in the history of geographical thought to successfully reconcile Greek geometric models with centuries of empirical data. By bridging these two worlds, he transformed astronomy from a philosophical exercise into a predictive science. He pioneered trigonometry by creating the first accurate, quantitative, geometric models for the Sun and Moon using a transcendental cycle system. Hipparchus’ greatest strength in this regard was his knowledge of the Babylonian “Goal-Year” treatise and the eclipse records of the 8th century BC, especially those of Nabonassar. He used this long-term data to calculate the average lunar month (Synodic Month) with incredible accuracy. His value was no less than a second in modern terms. He modeled the Sun with a simple offset circle and the Moon with a complex, moving great circle to explain the unequal length of the seasons. Hipparchus observed that the Sun revolved at the same speed on a circle, but the Earth moved away from the center, which caused the solar inequality. As a result of this inequality, Hipparchus determined the duration of the different seasons to be 94½ days for spring, 92½ days for summer, 88⅛ days for autumn, and 90⅛ days for winter, and showed that the seasons were not of equal length (i.e., spring was longer than autumn). That is, even though the Sun moves in a perfect circle at a constant speed, the Earth deviates from the center of that circle, which is called the Eccentric Model. On the other hand, he accurately measured the inclination of the Moon’s orbit towards the ecliptic and realized that the “Nodes” (points at which the orbits cross) recede in a cycle of 18.6 years. He developed a model based on epicycles to describe the motion of the Moon. Although his model did not perfectly match observations, it was still very advanced for its time and was later corrected by Ptolemy. Hipparchus of Nicaea

Hipparchus was one of the pioneers of ancient astronomy, which had a lasting influence on later times in this field. He not only criticized his predecessor Eratosthenes but also accelerated the history of geographical knowledge through his work. He is considered the founder of trigonometry, the originator of latitude-based climatology, the originator of the 24-hour time concept, the divider of the circle into 360°, and the inventor of various map projections. His work greatly influenced later geographers such as Ptolemy. ➣ Read in Hindi