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nicus in his model the sun entirely stationary lay at the center and all planets revolved around it 8 beyond the planets was the sphere of fixed stars also motionless this system presented two more unique ideas in addition to being heliocentric the earth rotated daily to create day night and the perceived motions of the other heavenly bodies and the sphere of fixed stars at its boundary were immensely distant from its center 9 this massive distance had to be assumed due to the fact that stars were observed to have no parallax which can only be explained by geocentricity or immense distances which create a parallax too small to be measured claudius ptolemy edit ptolemy 100 175 ad 5 summarized ideas about the cosmos through his mathematical models and his book mathematical syntaxis much more commonly known as the almagest 4 it was written around 150 ad and ptolemy declared that the stars placement in relation to each other and distances apart remained unchanged by the rotation of the heavens 5 he utilized a method using eclipses to find the star distances and calculated the distance of the moon based on parallax observations 10 shortly after he wrote a follow up called planetary hypotheses 10 ptolemy used and wrote about the geocentric system drawing greatly on traditional aristotelian physics 10 but using more complicated devices known as deferent and epicycles he borrowed from previous works by geometer apollonius of perga and astronomer hipparchus of nicaea 11 he declared that the stars are fixed within their celestial spheres but the spheres themselves are not fixed the rotations of these spheres thus explain the subtle movements of the constellations throughout the year 5 martianus capella edit martianus capella fl c 410 420 describes a modified geocentric model in which the earth is at rest in the center of the universe and circled by the moon the sun three planets and the stars while mercury and venus circle the sun all surrounded by the sphere of fixed stars 12 his model was not widely accepted despite his authority he was one of the earliest developers of the system of the seven liberal arts the trivium grammar logic and rhetoric and the quadrivium arithmetic geometry music astronomy that structured early medieval education 13 nonetheless his single encyclopedic work de nuptiis philologiae et mercurii on the marriage of philology and mercury also called de septem disciplinis on the seven disciplines was read taught and commented upon throughout the early middle ages and shaped european education during the early medieval period and the carolingian renaissance 14 nicolaus copernicus edit nicolaus copernicus 1473 1543 created a heliocentric system composed of orbs carrying each of the heavenly bodies 15 the final orb in his model was that of the fixed stars this final orb was the largest of his cosmos in both diameter and thickness this orb of stars is entirely fixed as the stars are embedded in the sphere and the sphere itself is immobile 15 the perceived motion of the stars therefore is created by the daily rotation of the earth about its axis tycho brahe edit tycho brahe s 1546 1601 system of the universe has been called geo heliocentric due to its twofold structure 9 at its center lies the stationary earth which is orbited by the moon and sun the planets then revolve about the sun while it revolves about the earth beyond all of these heavenly bodies lies a sphere of fixed stars 16 this sphere rotates about the stationary earth creating the perceived motion of the stars in the sky 16 this system has an interesting feature in that the sun and planets cannot be contained in solid orbs their orbs would collide but yet the stars are represented as being contained in a fixed sphere at the boundary of the cosmos 16 johannes kepler edit johannes kepler 1571 1630 was a devoted copernican following copernicus s models and ideas yet developing them 4 he was also an assistant of tycho brahe and he could access his patron s accurate measurements in his observational database kepler s mysterium cosmographicum 1596 a strong defense of the copernican system still pictures an image labelling the outmost celestial sphere as sphaera stellar fixar latin for sphere of fixed stars following the long held belief in such sphere this view was later superseded in his book astronomia nova 1609 where he established his laws of planetary motion 17 the mathematical basis for his own rudolphine tables which are working tables from which planetary positions could be shown 10 kepler s laws were the tipping point in finally disproving the old geocentric or ptolemaic cosmic theories and models 18 what was backed by the first uses of telescope by his contemporary galileo galilei also an advocate of copernicus estimated radius edit first greeks as many other ancient cultures thought of sky as it was a giant dome like structure only a few meters above the highest mountains the myth of atlas tells that this titan held the whole heavens on his shoulders 19 around 560 bc anaximander was the first to present a system where the celestial bodies turned at different distances but erroneously he thought the stars were closer to earth about 9 to 10 times the earth s size than the moon 18 19 times and the sun 27 28 times 20 nonetheless later pythagorians as philolaus around 400 bc also conceived a universe with orbiting bodies 21 thus assuming the fixed stars were at least a bit farther than the moon the sun and the rest of the planets meanwhile circa 450 bc anaxagoras was the first philosopher to consider the sun as a huge object larger than the land of peloponnesus 22 and consequently to realize how far from earth it might be he had suggested that the moon is rocky thus opaque and closer to the earth than the sun giving a correct explanation of eclipses 23 as far as the sun and the moon were conceived as spherical bodies and as they do not collide at solar eclipses this implies than the outer space should have some certain indeterminate depth eudoxus of cnidus in around 380 bc devised a geometric mathematical model for the movements of the planets based on conceptual concentric spheres centered on earth 24 and by 360 bc plato claimed in his timaeus that circles and spheres were the preferred shape of the universe and that the earth was at the centre and the stars forming the outermost shell followed by planets the sun and the moon 25 around 350 bc aristotle modified eudoxus model by supposing the spheres were material and crystalline 26 he was able to articulate the spheres for most planets however the spheres for jupiter and saturn crossed each other aristotle solved this complication by introducing an unrolled sphere by all these devices and even assuming the planets were star like single points the sphere of the fixed stars should implicitly be farther than previously thought around 280 bc aristarchus of samos offered the first definite discussion of the possibility of a heliocentric cosmos 27 and by geometrical means he estimated the moon s orbital radius at 60 earth radii and its physical radius as one third that of the earth he made an inaccurate attempt to measure the distance to the sun but sufficient to assert that the sun is much bigger than earth and it is much further away than the moon so the minor body the earth must orbit the major one the sun and not the opposite 28 this reasoning led him to assert that as stars do not show evident parallax viewed from earth along a single year they must be very very far away from the terrestrial surface and assuming they were all at the same distance from us he gave a relative estimation following the heliocentric ideas of aristarcus but not explicitly supporting them around 250 bc archimedes in his work the sand reckoner computes the diameter of the universe centered around the sun to be about 10 10 14 stadia in modern units about 2 light years 18 93 10 12 km 11 76 10 12 mi 29 in archimedes own words his aristarchus hypotheses are that the fixed stars and the sun remain unmoved that the earth revolves about the sun on the circumference of a circle the sun lying in the middle of the orbit and that the sphere of fixed stars situated about the same center as the sun is so great that the circle in which he supposes the earth to revolve bears such a proportion to the distance of the fixed stars as the center of the sphere bears to its surface 30 around 210 bc apollonius of perga shows the equivalence of two descriptions of the apparent retrograde motions of planets assuming the geocentric model one using eccentrics and another deferent and epicycles 11 in the following century measures of the sizes and distances of the earth and the moon improved around 200 bc eratosthenes determined that the radius of the earth is roughly 6 400 km 4 000 mi 31 circa 150 bc hipparchus used parallax to determine that the distance to the moon is roughly 380 000 km 236 100 mi 32 nearly matching aristarchus this imposed a minimum radius for the sphere of fixed stars at center to center earth to moon distance plus the moon s radius approx 1 3 earth radius plus the width of the sun it being at least the same that the moon plus the indeterminate thickness of the planets spheres believed to be thin anyway for a total about 386 400 km 240 100 mi this was around 24 500 000 times lower than archimedes computation the complexity to be described by the geocentric model around 130 ad ptolemy adopted apollonius epicycles in his geocentric model 33 epicycles are described as an orbit within an orbit for example looking at venus ptolemy claimed that it orbits the earth and as it orbits the earth it also orbits the original orbit riding a second minor local sphere ptolemy emphasised that the epicycle motion does not apply to the sun this device necessarily enlarges each of the celestial spheres thus making the outer sphere of the fixed stars yet larger when scholars applied ptolemy s epicycles they presumed that each planetary sphere was exactly thick enough to accommodate them 34 by combining this nested sphere model with astronomical observations scholars calculated what became generally accepted values at the time for the distances to the sun about 4 million kilometres 2 5 million miles and to the edge of the universe about 73 million kilometres 45 million miles 35 still around 130 000 times less than archimedes ptolemy s methods written in his almagest were accurate enough to keep them largely undisputed for more than 1 500 years 36 but by the european renaissance the possibility that such a huge sphere could complete a single revolution of 360 around the earth in only 24 hours was deemed improbable 37 and this point was one of the arguments of nicholas copernicus for leaving behind the centuries old geocentric model the highest upper bound ever given was by jewish astronomer levi ben gershon gersonides who circa 1300 estimated the distance to the fixed stars to be no less than 159 651 513 380 944 earth radii or about 100 000 light years in modern units 38 this was an overestimate although in the actual universe there are stars farther than that distance both in the milky way about three times wider and all the external galaxies the closest star from earth other than the sun is proxima centauri at about 4 25 light years only in other cultures edit the examples and perspective in this article may not represent a worldwide view of the subject you may improve this article discuss the issue on the talk page or create a new article as appropriate september 2024 learn how and when to remove this message in nordic mythology edit the attempts to explain the universe stem from observations of the objects found in the sky different cultures historically have various stories to provide an answer to the questions of what they are seeing norse mythology originates from northern europe around the geographical location of modern day region of scandinavia and northern germany the norse mythology consists of tales and myths derived from old norse which was a northern german language from the middle ages there is a series of manuscript texts written in old norse which contain a collection of 35 poems written from oral tradition 39 among historians there seems to be speculation of the specific dates of the poems written however the estimated record of the texts is around the beginning of the thirteenth century 40 although the oral tradition of passing down tales existed long before the advent of text manuscripts and print versions among surviving texts there is mention of the mythological god odin scholars have recounted the tale of the αesir gods creation myth which includes the idea of fixed stars found within the teleology of the tale padaric colum has written a book the children of odin which in much detail reiterates the story of how the aesir gods brought the giant named ymir to his demise and created the world from his body affixing sparks from the fiery muspelheim or the fixed stars to the dome of the sky which was the skull of ymir 41 the norse creation myth is one of several cases which treated stars as being fixed to a sphere beyond the earth later scientific literature shows astronomical thought which kept a version of this idea until the seventeenth century developing western astronomy edit copernicus nicolaus on the revolutions of the heavenly spheres nüremberg 1543 print copy of copernicus s work showing the model of the universe with the sun in the center and a sphere of immobile stars on the outside according to his theory of the cosmos western astronomical knowledge was based on the traditional thoughts from philosophical and observational inquiries of greek antiquity other cultures contributed to thought about the fixed stars including the babylonians who from the eighteenth to the sixth century bc constructed constellation maps maps of the stars and the idea of mythological stories to explain them were largely being acquired all over the world and in several cultures one similarity between them all was the preliminary understanding that the stars were fixed and immobile in the universe this understanding was incorporated into theorized models and mathematical representations of the cosmos by philosophers like anaximander and aristotle from the ancient greeks anaximander proposed this original and erroneous order of the celestial objects above the earth first a nearest layer with the fixed stars plus planets then another layer with the moon and finally an outer one with the sun to him the stars as well as the sun and moon were apertures of wheel like condensations filled with fire 42 all other later models of the planetary system show a celestial sphere containing fixed stars on the outermost part of the universe its edge within it lie all the rest of the moving luminaires plato aristotle and other like greek thinkers of antiquity and later the ptolemaic model of the cosmos showed an earth centered universe ptolemy was influential w...
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