Aglaonice or Aganice of Thessaly was a Greek astronomer of the 2nd or 1st century BC. She is mentioned in the writings of Plutarch and in the scholia to Apollonius of Rhodes as a female astronomer and as the daughter of Hegetor of Thessaly, she was regarded as a sorceress for her ability to make the Moon disappear from the sky, taken to mean she could predict the time and general area where a lunar eclipse would occur. A Greek proverb makes reference to Aglaonice's alleged boasting: "Yes, as the moon obeys Aglaonice". A number of female astrologers regarded as sorcerers, were associated with Aglaonice, they were known as the "witches of Thessaly" and were active from the 3rd to 1st centuries BC. In Plato's Gorgias, Socrates speaks of "the Thessalian enchantresses, who, as they say, bring down the moon from heaven at the risk of their own perdition."Plutarch wrote that she was "thoroughly acquainted with the periods of the full moon when it is subject to eclipse, knowing beforehand the time when the moon was due to be overtaken by the earth's shadow, imposed upon the women, made them all believe that she was drawing down the moon."One of the craters on Venus is named after Aglaonice.
As "Aglaonice", she is a character in the Jean Cocteau film Orpheus, where she is a friend of Eurydice and leader of the League of Women. Aglaonice is a featured figure on Judy Chicago's installation piece The Dinner Party, being represented as one of the 999 names on the Heritage Floor. Timeline of women in science This article incorporates text from a publication now in the public domain: Smith, William, ed.. "Aganice". Dictionary of Greek and Roman Biography and Mythology
Autolycus of Pitane
Autolycus of Pitane was a Greek astronomer and geographer. The lunar crater Autolycus was named in his honour. Autolycus was born in a town of Aeolis within Ionia, Asia Minor. Of his personal life nothing is known, although he was a contemporary of Aristotle and his works seem to have been completed in Athens between 335–300 BC. Euclid references some of Autolycus' work, Autolycus is known to have taught Arcesilaus. Autolycus' surviving works include a book on spheres entitled On the Moving Sphere and another On Risings and Settings of celestial bodies. Autolycus' works were translated by Maurolycus in the sixteenth century. On the Moving Sphere is believed to be the oldest mathematical treatise from ancient Greece, preserved. All Greek mathematical works prior to Autolycus' Sphere are taken from summaries, commentaries, or descriptions of the works. One reason for its survival is that it had been a part of a used collection called "Little Astronomy", preserved by translation into Arabic in the 9th century.
In Europe it was lost, but was brought back during the Crusades in the 12th century, translated back into Latin. In his Sphere, Autolycus studied the characteristics and movement of a sphere; the work is simple and not original, since it consists of only elementary theorems on spheres that would be needed by astronomers, but its theorems are enunciated and proved. Its prime significance, therefore, is that it indicates that by his day there was a established textbook tradition in geometry, today regarded as typical of classical Greek geometry; the theorem statement is enunciated, a figure of the construction is given alongside the proof, a concluding remark is made. Moreover, it gives indications of. Two hundred years Theodosius' wrote Sphaerics, a book, believed to have a common origin with On the Moving Sphere in some pre-Euclidean textbook written by Eudoxus. In astronomy, Autolycus studied the relationship between the rising and the setting of the celestial bodies in his treatise in two books entitled On Risings and Settings.
The second book is an expansion of his first book and of higher quality. He wrote that "any star which rises and sets always rises and sets at the same point in the horizon." Autolycus relied on Eudoxus' astronomy and was a strong supporter of Eudoxus' theory of homocentric spheres. Boyer, Carl B.. A History of Mathematics. John Wiley & Sons, Inc. ISBN 0-471-54397-7. Huxley, G. L.. "Autolycus of Pitane". Dictionary of Scientific Biography. 1. New York: Charles Scribner's Sons. Pp. 338–39. ISBN 0-684-10114-9. On line at "Autolycus of Pitane". HighBeam Research. Retrieved 26 March 2015. O'Connor, John J.. Autolycus On The Moving Sphere from the Million Books Project ΠΕΡΙ ΚΙΝΟΥΜΕΝΗΣ ΣΦΑΙΡΑΣ and ΠΕΡΙ ΕΠΙΤΟΛΩΝ ΚΑΙ ΔΥΣΕΩΝ
Eratosthenes of Cyrene was a Greek mathematician, poet and music theorist. He was a man of becoming the chief librarian at the Library of Alexandria, he invented the discipline of geography, including the terminology used today. He is best known for being the first person to calculate the circumference of the Earth, which he did by comparing angles of the mid-day Sun at two places a known North-South distance apart, his calculation was remarkably accurate. He was the first to calculate the tilt of the Earth's axis, again with remarkable accuracy. Additionally, he may have calculated the distance from the Earth to the Sun and invented the leap day, he created the first map of the world, incorporating parallels and meridians based on the available geographic knowledge of his era. Eratosthenes was the founder of scientific chronology. Eratosthenes dated The Sack of Troy to 1183 BC. In number theory, he introduced the sieve of Eratosthenes, an efficient method of identifying prime numbers, he was a figure of influence in many fields.
According to an entry in the Suda, his critics scorned him, calling him Beta because he always came in second in all his endeavors. Nonetheless, his devotees nicknamed him Pentathlos after the Olympians who were well rounded competitors, for he had proven himself to be knowledgeable in every area of learning. Eratosthenes yearned to understand the complexities of the entire world; the son of Aglaos, Eratosthenes was born in 276 BC in Cyrene. Now part of modern-day Libya, Cyrene had been founded by Greeks centuries earlier and became the capital of Pentapolis, a country of five cities: Cyrene, Berenice and Apollonia. Alexander the Great conquered Cyrene in 332 BC, following his death in 323 BC, its rule was given to one of his generals, Ptolemy I Soter, the founder of the Ptolemaic Kingdom. Under Ptolemaic rule the economy prospered, based on the export of horses and silphium, a plant used for rich seasoning and medicine. Cyrene became a place of cultivation. Like any young Greek, Eratosthenes would have studied in the local gymnasium, where he would have learned physical skills and social discourse as well as reading, arithmetic and music.
Eratosthenes went to Athens to further his studies. There he was taught Stoicism by its founder, Zeno of Citium, in philosophical lectures on living a virtuous life, he studied under Aristo of Chios, who led a more cynical school of philosophy. He studied under the head of the Platonic Academy, Arcesilaus of Pitane, his interest in Plato led him to write his first work at a scholarly level, inquiring into the mathematical foundation of Plato's philosophies. Eratosthenes investigated the art of poetry under Callimachus, he was a imaginative poet. He wrote poems: one in hexameters called Hermes, illustrating the god's life history, he wrote Chronographies, a text that scientifically depicted dates of importance, beginning with the Trojan War. This work was esteemed for its accuracy. George Syncellus was able to preserve from Chronographies a list of 38 kings of the Egyptian Thebes. Eratosthenes wrote Olympic Victors, a chronology of the winners of the Olympic Games, it is not known when he wrote his works.
These works and his great poetic abilities led the pharaoh Ptolemy III Euergetes to seek to place him as a librarian at the Library of Alexandria in the year 245 BC. Eratosthenes thirty years old, accepted Ptolemy's invitation and traveled to Alexandria, where he lived for the rest of his life. Within about five years he became Chief Librarian, a position that the poet Apollonius Rhodius had held; as head of the library Eratosthenes tutored the children of Ptolemy, including Ptolemy IV Philopator who became the fourth Ptolemaic pharaoh. He expanded the library's holdings: in Alexandria all books had to be surrendered for duplication, it was said that these were copied so that it was impossible to tell if the library had returned the original or the copy. He sought to maintain the reputation of the Library of Alexandria against competition from the Library of Pergamum. Eratosthenes created a whole section devoted to the examination of Homer, acquired original works of great tragic dramas of Aeschylus and Euripides.
Eratosthenes made several important contributions to mathematics and science, was a friend of Archimedes. Around 255 BC, he invented the armillary sphere. In On the Circular Motions of the Celestial Bodies, Cleomedes credited him with having calculated the Earth's circumference around 240 BC, using knowledge of the angle of elevation of the Sun at noon on the summer solstice in Alexandria and on Elephantine Island near Syene. Eratosthenes believed there was good and bad in every nation and criticized Aristotle for arguing that humanity was divided into Greeks and barbarians, that the Greeks should keep themselves racially pure; as he aged he contracted ophthalmia, becoming blind around 195 BC. Losing the ability to read and to observe nature plagued and depressed him, leading him to voluntarily starve himself to death, he died in 194 BC at 82 in Alexandria. Eratosthenes calculated the Earth's circumference without leaving Alexandria, he knew that at local noon on the summer solstice in Syene (modern Asw
Earth is the third planet from the Sun and the only astronomical object known to harbor life. According to radiometric dating and other sources of evidence, Earth formed over 4.5 billion years ago. Earth's gravity interacts with other objects in space the Sun and the Moon, Earth's only natural satellite. Earth revolves around the Sun in a period known as an Earth year. During this time, Earth rotates about its axis about 366.26 times. Earth's axis of rotation is tilted with respect to its orbital plane; the gravitational interaction between Earth and the Moon causes ocean tides, stabilizes Earth's orientation on its axis, slows its rotation. Earth is the largest of the four terrestrial planets. Earth's lithosphere is divided into several rigid tectonic plates that migrate across the surface over periods of many millions of years. About 71% of Earth's surface is covered with water by oceans; the remaining 29% is land consisting of continents and islands that together have many lakes and other sources of water that contribute to the hydrosphere.
The majority of Earth's polar regions are covered in ice, including the Antarctic ice sheet and the sea ice of the Arctic ice pack. Earth's interior remains active with a solid iron inner core, a liquid outer core that generates the Earth's magnetic field, a convecting mantle that drives plate tectonics. Within the first billion years of Earth's history, life appeared in the oceans and began to affect the Earth's atmosphere and surface, leading to the proliferation of aerobic and anaerobic organisms; some geological evidence indicates. Since the combination of Earth's distance from the Sun, physical properties, geological history have allowed life to evolve and thrive. In the history of the Earth, biodiversity has gone through long periods of expansion punctuated by mass extinction events. Over 99% of all species that lived on Earth are extinct. Estimates of the number of species on Earth today vary widely. Over 7.6 billion humans live on Earth and depend on its biosphere and natural resources for their survival.
Humans have developed diverse cultures. The modern English word Earth developed from a wide variety of Middle English forms, which derived from an Old English noun most spelled eorðe, it has cognates in every Germanic language, their proto-Germanic root has been reconstructed as *erþō. In its earliest appearances, eorðe was being used to translate the many senses of Latin terra and Greek γῆ: the ground, its soil, dry land, the human world, the surface of the world, the globe itself; as with Terra and Gaia, Earth was a personified goddess in Germanic paganism: the Angles were listed by Tacitus as among the devotees of Nerthus, Norse mythology included Jörð, a giantess given as the mother of Thor. Earth was written in lowercase, from early Middle English, its definite sense as "the globe" was expressed as the earth. By Early Modern English, many nouns were capitalized, the earth became the Earth when referenced along with other heavenly bodies. More the name is sometimes given as Earth, by analogy with the names of the other planets.
House styles now vary: Oxford spelling recognizes the lowercase form as the most common, with the capitalized form an acceptable variant. Another convention capitalizes "Earth" when appearing as a name but writes it in lowercase when preceded by the, it always appears in lowercase in colloquial expressions such as "what on earth are you doing?" The oldest material found in the Solar System is dated to 4.5672±0.0006 billion years ago. By 4.54±0.04 Bya the primordial Earth had formed. The bodies in the Solar System evolved with the Sun. In theory, a solar nebula partitions a volume out of a molecular cloud by gravitational collapse, which begins to spin and flatten into a circumstellar disk, the planets grow out of that disk with the Sun. A nebula contains gas, ice grains, dust. According to nebular theory, planetesimals formed by accretion, with the primordial Earth taking 10–20 million years to form. A subject of research is the formation of some 4.53 Bya. A leading hypothesis is that it was formed by accretion from material loosed from Earth after a Mars-sized object, named Theia, hit Earth.
In this view, the mass of Theia was 10 percent of Earth, it hit Earth with a glancing blow and some of its mass merged with Earth. Between 4.1 and 3.8 Bya, numerous asteroid impacts during the Late Heavy Bombardment caused significant changes to the greater surface environment of the Moon and, by inference, to that of Earth. Earth's atmosphere and oceans were formed by volcanic outgassing. Water vapor from these sources condensed into the oceans, augmented by water and ice from asteroids and comets. In this model, atmospheric "greenhouse gases" kept the oceans from freezing when the newly forming Sun had only 70% of its current luminosity. By 3.5 Bya, Earth's magnetic field was established, which helped prevent the atmosphere from being stripped away by the solar wind. A crust formed; the two models that explain land mass propose either a steady growth to the present-day forms or, more a rapid growth early in Earth history followed by a long-term steady continental area. Continents formed by plate tectonics
The Sun is the star at the center of the Solar System. It is a nearly perfect sphere of hot plasma, with internal convective motion that generates a magnetic field via a dynamo process, it is by far the most important source of energy for life on Earth. Its diameter is about 1.39 million kilometers, or 109 times that of Earth, its mass is about 330,000 times that of Earth. It accounts for about 99.86% of the total mass of the Solar System. Three quarters of the Sun's mass consists of hydrogen; the Sun is a G-type main-sequence star based on its spectral class. As such, it is informally and not accurately referred to as a yellow dwarf, it formed 4.6 billion years ago from the gravitational collapse of matter within a region of a large molecular cloud. Most of this matter gathered in the center, whereas the rest flattened into an orbiting disk that became the Solar System; the central mass became so hot and dense that it initiated nuclear fusion in its core. It is thought that all stars form by this process.
The Sun is middle-aged. It fuses about 600 million tons of hydrogen into helium every second, converting 4 million tons of matter into energy every second as a result; this energy, which can take between 10,000 and 170,000 years to escape from its core, is the source of the Sun's light and heat. In about 5 billion years, when hydrogen fusion in its core has diminished to the point at which the Sun is no longer in hydrostatic equilibrium, its core will undergo a marked increase in density and temperature while its outer layers expand to become a red giant, it is calculated that the Sun will become sufficiently large to engulf the current orbits of Mercury and Venus, render Earth uninhabitable. After this, it will shed its outer layers and become a dense type of cooling star known as a white dwarf, no longer produce energy by fusion, but still glow and give off heat from its previous fusion; the enormous effect of the Sun on Earth has been recognized since prehistoric times, the Sun has been regarded by some cultures as a deity.
The synodic rotation of Earth and its orbit around the Sun are the basis of solar calendars, one of, the predominant calendar in use today. The English proper name Sun may be related to south. Cognates to English sun appear in other Germanic languages, including Old Frisian sunne, Old Saxon sunna, Middle Dutch sonne, modern Dutch zon, Old High German sunna, modern German Sonne, Old Norse sunna, Gothic sunnō. All Germanic terms for the Sun stem from Proto-Germanic *sunnōn; the Latin name for the Sun, Sol, is not used in everyday English. Sol is used by planetary astronomers to refer to the duration of a solar day on another planet, such as Mars; the related word solar is the usual adjectival term used for the Sun, in terms such as solar day, solar eclipse, Solar System. A mean Earth solar day is 24 hours, whereas a mean Martian'sol' is 24 hours, 39 minutes, 35.244 seconds. The English weekday name Sunday stems from Old English and is a result of a Germanic interpretation of Latin dies solis, itself a translation of the Greek ἡμέρα ἡλίου.
The Sun is a G-type main-sequence star. The Sun has an absolute magnitude of +4.83, estimated to be brighter than about 85% of the stars in the Milky Way, most of which are red dwarfs. The Sun is heavy-element-rich, star; the formation of the Sun may have been triggered by shockwaves from more nearby supernovae. This is suggested by a high abundance of heavy elements in the Solar System, such as gold and uranium, relative to the abundances of these elements in so-called Population II, heavy-element-poor, stars; the heavy elements could most plausibly have been produced by endothermic nuclear reactions during a supernova, or by transmutation through neutron absorption within a massive second-generation star. The Sun is by far the brightest object in the Earth's sky, with an apparent magnitude of −26.74. This is about 13 billion times brighter than the next brightest star, which has an apparent magnitude of −1.46. The mean distance of the Sun's center to Earth's center is 1 astronomical unit, though the distance varies as Earth moves from perihelion in January to aphelion in July.
At this average distance, light travels from the Sun's horizon to Earth's horizon in about 8 minutes and 19 seconds, while light from the closest points of the Sun and Earth takes about two seconds less. The energy of this sunlight supports all life on Earth by photosynthesis, drives Earth's climate and weather; the Sun does not have a definite boundary, but its density decreases exponentially with increasing height above the photosphere. For the purpose of measurement, the Sun's radius is considered to be the distance from its center to the edge of the photosphere, the apparent visible surface of the Sun. By this measure, the Sun is a near-perfect sphere with an oblateness estimated at about 9 millionths, which means that its polar diameter differs from its equatorial diameter by only 10 kilometres; the tidal effect of the planets is weak and does not affect the shape of the Sun. The Sun rotates faster at its equator than at its poles; this differential rotation is caused by convective motion
Parallax is a displacement or difference in the apparent position of an object viewed along two different lines of sight, is measured by the angle or semi-angle of inclination between those two lines. Due to foreshortening, nearby objects show a larger parallax than farther objects when observed from different positions, so parallax can be used to determine distances. To measure large distances, such as the distance of a planet or a star from Earth, astronomers use the principle of parallax. Here, the term parallax is the semi-angle of inclination between two sight-lines to the star, as observed when Earth is on opposite sides of the Sun in its orbit; these distances form the lowest rung of what is called "the cosmic distance ladder", the first in a succession of methods by which astronomers determine the distances to celestial objects, serving as a basis for other distance measurements in astronomy forming the higher rungs of the ladder. Parallax affects optical instruments such as rifle scopes, binoculars and twin-lens reflex cameras that view objects from different angles.
Many animals, including humans, have two eyes with overlapping visual fields that use parallax to gain depth perception. In computer vision the effect is used for computer stereo vision, there is a device called a parallax rangefinder that uses it to find range, in some variations altitude to a target. A simple everyday example of parallax can be seen in the dashboard of motor vehicles that use a needle-style speedometer gauge; when viewed from directly in front, the speed may show 60. As the eyes of humans and other animals are in different positions on the head, they present different views simultaneously; this is the basis of stereopsis, the process by which the brain exploits the parallax due to the different views from the eye to gain depth perception and estimate distances to objects. Animals use motion parallax, in which the animals move to gain different viewpoints. For example, pigeons down to see depth; the motion parallax is exploited in wiggle stereoscopy, computer graphics which provide depth cues through viewpoint-shifting animation rather than through binocular vision.
Parallax arises due to change in viewpoint occurring due to motion of the observer, of the observed, or of both. What is essential is relative motion. By observing parallax, measuring angles, using geometry, one can determine distance. Astronomers use the word "parallax" as a synonym for "distance measurement" by other methods: see parallax #Astronomy. Stellar parallax created by the relative motion between the Earth and a star can be seen, in the Copernican model, as arising from the orbit of the Earth around the Sun: the star only appears to move relative to more distant objects in the sky. In a geostatic model, the movement of the star would have to be taken as real with the star oscillating across the sky with respect to the background stars. Stellar parallax is most measured using annual parallax, defined as the difference in position of a star as seen from the Earth and Sun, i. e. the angle subtended at a star by the mean radius of the Earth's orbit around the Sun. The parsec is defined as the distance.
Annual parallax is measured by observing the position of a star at different times of the year as the Earth moves through its orbit. Measurement of annual parallax was the first reliable way to determine the distances to the closest stars; the first successful measurements of stellar parallax were made by Friedrich Bessel in 1838 for the star 61 Cygni using a heliometer. Stellar parallax remains the standard for calibrating other measurement methods. Accurate calculations of distance based on stellar parallax require a measurement of the distance from the Earth to the Sun, now based on radar reflection off the surfaces of planets; the angles involved in these calculations are small and thus difficult to measure. The nearest star to the Sun, Proxima Centauri, has a parallax of 0.7687 ± 0.0003 arcsec. This angle is that subtended by an object 2 centimeters in diameter located 5.3 kilometers away. The fact that stellar parallax was so small that it was unobservable at the time was used as the main scientific argument against heliocentrism during the early modern age.
It is clear from Euclid's geometry that the effect would be undetectable if the stars were far enough away, but for various reasons such gigantic distances involved seemed implausible: it was one of Tycho's principal objections to Copernican heliocentrism that in order for it to be compatible with the lack of observable stellar parallax, there would have to be an enormous and unlikely void between the orbit of Saturn and the eighth sphere. In 1989, the satellite Hipparcos was launched for obtaining improved parallaxes and proper motions for over 100,000 nearby stars, increasing the reach of the method tenfold. So, Hipparcos is only able to measure parallax angles for stars up to about 1,600 light-years away, a little more than one percent of the diameter of the Milky Way Galaxy; the European Space Agency's Gaia mission, launched in December 2013, will be able to measure parallax angles to an accuracy of 10 microarcseconds, thus mapping nearby stars up to a distance of tens of thousands of ligh
Aratus was a Greek didactic poet. His major extant work is his hexameter poem Phenomena, the first half of, a verse setting of a lost work of the same name by Eudoxus of Cnidus, it describes other celestial phenomena. The second half is called the Diosemeia, is chiefly about weather lore. Although Aratus was somewhat ignorant of Greek astronomy, his poem was popular in the Greek and Roman world, as is proved by the large number of commentaries and Latin translations, some of which survive. There are several accounts of Aratus' life by anonymous Greek writers, the Suda and Eudocia mention him. From these it appears, he is known to have studied with Menecrates in Philitas in Cos.. As a disciple of the Peripatetic philosopher Praxiphanes, in Athens, he met the Stoic philosopher Zeno, as well as Callimachus of Cyrene and Menedemus, the founder of the Eretrian school. About 276 BC Aratus was invited to the court of the Macedonian king Antigonus II Gonatas, whose victory over the Gauls in 277 Aratus set to verse.
Here he wrote Phenomena. He spent some time at the court of Antiochus I Soter of Syria, but subsequently returned to Pella in Macedon, where he died sometime before 240/239, his chief pursuits were medicine and philosophy. Several poetical works on various subjects, as well as a number of prose epistles, are attributed to Aratus, but none of them have come down to us, except his two astronomical poems in hexameter; these have been joined together as if parts of the same work. The Phenomena appears to be based on two prose works—Phenomena and Enoptron —by Eudoxus of Cnidus, written about a century earlier. We are told by the biographers of Aratus that it was the desire of Antigonus to have them turned into verse, which gave rise to the Phenomena of Aratus; the purpose of the Phenomena is to give an introduction to the constellations, with the rules for their risings and settings. The positions of the constellations, north of the ecliptic, are described by reference to the principal groups surrounding the north pole, whilst Orion serves as a point of departure for those to the south.
The immobility of the earth, the revolution of the sky about a fixed axis are maintained. The opening of the poem asserts the dependence of all things upon Zeus. From the lack of precision in the descriptions, it would seem that Aratus was neither a mathematician nor observer or, at any rate, that in this work he did not aim at scientific accuracy, he not only represents the configurations of particular groups incorrectly, but describes some phenomena which are inconsistent with any one supposed latitude of the spectator, others which could not coexist at any one epoch. These errors are to be attributed to Eudoxus himself, to the way in which Aratus has used the materials supplied by him. Hipparchus, a scientific astronomer and observer, has left a commentary upon the Phenomenas of Eudoxus and Aratus, accompanied by the discrepancies which he had noticed between his own observations and their descriptions; the Diosemeia consists of forecasts of the weather from astronomical phenomena, with an account of its effects upon animals.
It appears to be an imitation of Hesiod, to have been imitated by Virgil in some parts of the Georgics. The materials are said to be taken wholly from Aristotle's Meteorologica, from the work of Theophrastus, On Weather Signs, from Hesiod. Nothing is said in either poem about Hellenistic astrology; the two poems were popular both in the Greek and Roman world, as is proved by the number of commentaries and Latin translations. He enjoyed immense prestige among Hellenistic poets, including Theocritus and Leonidas of Tarentum; this assessment was picked up including Ovid and Virgil. Latin versions were made by none other than Cicero, the member of the imperial Julio-Claudian dynasty Germanicus, the less-famous Avienus. Quintilian was less enthusiastic. Aratus was cited by the author of Acts, in 17.28, where he relates Saint Paul's address on the Areopagus. Paul, speaking of God, quotes the fifth line of Aratus's Phenomena: Authors of twenty-seven commentaries are known. An Arabic translation was commissioned in the ninth century by the Caliph Al-Ma'mun.
He is cited by Stephanus of Byzantium and Stobaeus. Several accounts of his life are extant, by anonymous Greek writers; the crater Aratus on the Moon and the minor planet 12152 Aratus are named in his honour. The H