Ancient Greek astronomy in the context of "Antikythera mechanism"

Archimedes of Syracuse (/ˌɑːrkɪˈmiːdiːz/ AR-kih-MEE-deez; c. 287 – c. 212 BC) was an Ancient Greek mathematician, physicist, engineer, astronomer, and inventor from the city of Syracuse in Sicily. Although few details of his life are known, based on his surviving work, he is considered one of the leading scientists in classical antiquity, and one of the greatest mathematicians of all time. Archimedes anticipated modern calculus and analysis by applying the concept of the infinitesimals and the method of exhaustion to derive and rigorously prove many geometrical theorems, including the area of a circle, the surface area and volume of a sphere, the area of an ellipse, the area under a parabola, the volume of a segment of a paraboloid of revolution, the volume of a segment of a hyperboloid of revolution, and the area of a spiral.

Archimedes' other mathematical achievements include deriving an approximation of pi (π), defining and investigating the Archimedean spiral, and devising a system using exponentiation for expressing very large numbers. He was also one of the first to apply mathematics to physical phenomena, working on statics and hydrostatics. Archimedes' achievements in this area include a proof of the law of the lever, the widespread use of the concept of center of gravity, and the enunciation of the law of buoyancy known as Archimedes' principle. In astronomy, he made measurements of the apparent diameter of the Sun and the size of the universe. He is also said to have built a planetarium device that demonstrated the movements of the known celestial bodies, and may have been a precursor to the Antikythera mechanism. He is also credited with designing innovative machines, such as his screw pump, compound pulleys, and defensive war machines to protect his native Syracuse from invasion.

Hipparchus (/hɪˈpɑːrkəs/; Greek: Ἵππαρχος, Hípparkhos; c. 190 – c. 120 BC) was a Greek astronomer, geographer, and mathematician. He is considered the founder of trigonometry, but is most famous for his incidental discovery of the precession of the equinoxes. Hipparchus was born in Nicaea, Bithynia, and probably died on the island of Rhodes, Greece. He is known to have been a working astronomer between 162 and 127 BC.

Hipparchus is considered the greatest ancient astronomical observer and, by some, the greatest overall astronomer of antiquity. He was the first whose quantitative and accurate models for the motion of the Sun and Moon survive. For this he certainly made use of the observations and perhaps the mathematical techniques accumulated over centuries by the Babylonians and by Meton of Athens (fifth century BC), Timocharis, Aristyllus, Aristarchus of Samos, and Eratosthenes, among others.

Early Greek cosmology refers to beliefs about the origins, development, and structure of the universe in Ancient Greece that existed before the development of Ancient Greek astronomy. The basic elements of this early cosmology included a flat earth, heaven, a cosmic ocean, the afterworld (Hades), and the netherworld (Tartarus). The first three were represented by the gods Gaia, Uranus, and Oceanus (or sometimes Pontus). Ancient Greek cosmology was related to ancient Near Eastern cosmology, and was ultimately replaced by a more systematic and demythologized approach found in ancient Greek astronomy. Its main sources are the poetry of Homer (the Iliad and the Odyssey), Hesiod (the Theogony and the Works and Days), and surviving fragments from Mimnermus.

Beginning in the 5th century BC, elements of the traditional Greek cosmos began to be modified and challenged. One of the earliest of these challenges came from the emergence of the view that the cosmos as a whole was spherical (advocated by Xenophanes, Parmenides, Empedocles, and others). The rotation of the spherical cosmos was said to explain the visible rotation of the stars (an idea called "vortex"). Soon, a spherical model of the earth itself was proposed, which gradually gained acceptance, although the flat earth view never entirely disappeared during either classical antiquity or late antiquity, continuing to receive support from geographers and others like Ctesias, Ephorus, Strabo, Tacitus, and the Epicureans. The last Greek advocate of the traditional cosmology was Cosmas Indicopleustes.

Babylonian astronomy was the study or recording of celestial objects during the early history of Mesopotamia. The numeral system used, sexagesimal, was based on 60, as opposed to ten in the modern decimal system. This system simplified the calculating and recording of unusually great and small numbers.

During the 8th and 7th centuries BC, Babylonian astronomers developed a new empirical approach to astronomy. They began studying and recording their belief system and philosophies dealing with an ideal nature of the universe and began employing an internal logic within their predictive planetary systems. This was an important contribution to astronomy and the philosophy of science, and some modern scholars have thus referred to this approach as a scientific revolution. This approach to astronomy was adopted and further developed in Greek and Hellenistic astrology. Classical Greek and Latin sources frequently use the term Chaldeans for the philosophers, who were considered as priest-scribes specializing in astronomical and other forms of divination. Babylonian astronomy paved the way for modern astrology and is responsible for its spread across the Graeco-Roman empire during the 2nd-century Hellenistic Period. The Babylonians used the sexagesimal system to trace the planets' transits, by dividing the 360 degree sky into 30 degrees, they assigned 12 zodiacal signs to the stars along the ecliptic.

Eudoxus of Cnidus (/ˈjuːdəksəs/; Ancient Greek: Εὔδοξος ὁ Κνίδιος, Eúdoxos ho Knídios; c. 390 – c. 340 BC) was an ancient Greek astronomer, mathematician, doctor, and lawmaker. He was a student of Archytas and Plato. All of his original works are lost, though some fragments are preserved in Hipparchus's Commentaries on the Phenomena of Aratus and Eudoxus. Spherics by Theodosius of Bithynia may be based on a work by Eudoxus.

Aristarchus of Samos (/ˌærəˈstɑːrkəs/; Ancient Greek: Ἀρίσταρχος ὁ Σάμιος, Aristarkhos ho Samios; c. 310 – c. 230 BC) was an ancient Greek astronomer and mathematician who presented the first known heliocentric model that placed the Sun at the center of the universe, with the Earth revolving around the Sun once a year and rotating about its axis once a day. He also supported the theory of Anaxagoras that the Sun was just another star.

He likely moved to Alexandria, and he was a student of Strato of Lampsacus, who later became the head of the Peripatetic school in Greece. According to Ptolemy, Aristarchus observed the summer solstice of 280 BC. Vitruvius writes that Aristarchus built two different sundials: one a flat disc; and one hemispherical. Aristarchus estimated the sizes of the Sun and Moon as compared to Earth, and the distances from the Earth to the Sun and to the Moon. His estimate that the Sun was 7 times larger than Earth (actually 109 times) brought about the further insight that the Sun's greater size made it the most natural central point of the universe, as opposed to Earth.

The cosmology of the ancient Near East refers to beliefs about where the universe came from, how it developed, and its physical layout, in the ancient Near East, an area that corresponds with the Middle East today (including Mesopotamia, Egypt, Persia, the Levant, Anatolia, and the Arabian Peninsula). The basic understanding of the world in this region from premodern times included a flat earth, a solid layer or barrier above the sky (the firmament), a cosmic ocean located above the firmament, a region above the cosmic ocean where the gods lived, and a netherworld located at the furthest region in the direction down. Creation myths explained where the universe came from, including which gods created it (and how), as well as how humanity was created. These beliefs are attested as early as the fourth millennium BC and dominated until the modern era, with the only major competing system being the Hellenistic cosmology that developed in Ancient Greece in the mid-1st millennium BC.

Geographically, these views are known from the Mesopotamian cosmologies from Babylonia, Sumer, and Akkad; the Levantine or West Semitic cosmologies from Ugarit and ancient Israel and Judah (the biblical cosmology); the Egyptian cosmology from Ancient Egypt; and the Anatolian cosmologies from the Hittites. This system of cosmology went on to have a profound influence on views in early Greek cosmology, later Jewish cosmology, patristic cosmology, and Islamic cosmology (including Quranic cosmology).

Ammonius Hermiae (/əˈmoʊniəs/; Ancient Greek: Ἀμμώνιος ὁ Ἑρμείου, romanized: Ammōnios ho Hermeiou, lit. 'Ammonius, son of Hermias'; c. 440 – between 517 and 526) was a Greek philosopher from Alexandria in the eastern Roman empire during Late Antiquity. A Neoplatonist, he was the son of the philosophers Hermias and Aedesia, the brother of Heliodorus of Alexandria and the grandson of Syrianus. Ammonius was a pupil of Proclus in Roman Athens, and taught at Alexandria for most of his life, having obtained a public chair in the 470s.

According to Olympiodorus of Thebes's Commentaries on Plato's Gorgias and Phaedo texts, Ammonius gave lectures on the works of Plato, Aristotle, and Porphyry of Tyre, and wrote commentaries on Aristotelian works and three lost commentaries on Platonic texts. He is also the author of a text on the astrolabe published in the Catalogus Codicum Astrologorum Graecorum, and lectured on astronomy and geometry. Ammonius taught numerous Neoplatonists, including Damascius, Olympiodorus of Thebes, John Philoponus, Simplicius of Cilicia, and Asclepius of Tralles. Also among his pupils were the physician Gessius of Petra and the ecclesiastical historian Zacharias Rhetor, who became the bishop of Mytilene.

Apparent magnitude (m) is a measure of the brightness of a star, astronomical object or other celestial objects like artificial satellites. Its value depends on its intrinsic luminosity, its distance, and any extinction of the object's light caused by interstellar dust or atmosphere along the line of sight to the observer.

Unless stated otherwise, the word magnitude in astronomy usually refers to a celestial object's apparent magnitude. The magnitude scale likely dates to before the ancient Roman astronomer Claudius Ptolemy, whose star catalog popularized the system by listing stars from 1st magnitude (brightest) to 6th magnitude (dimmest). The modern scale was mathematically defined to closely match this historical system by Norman Pogson in 1856.