Medieval and Renaissance Astronomy - Lecture Notes NETs 1745

‭Medieval and Renaissance Astronomy‬ ‭Astronomy in the Dark Ages:‬ ‭●‬ ‭Dark Ages (5th-7th C):‬‭Church-state merger led to‬‭decline in science‬ ‭-‬ ‭Ancient Greek theories were rejected as contrary to Scripture‬ ‭-‬ ‭Loss of Ancient Greek texts (Latin became the official language of‬ ‭scholarship)‬ ‭The Rise of Islamic Astronomy:‬ ‭●‬ ‭Islamic Astronomy (9-13th C):‬ ‭-‬ ‭Qur'an encourages knowledge of the sky for time-keeping.‬ ‭-‬ ‭Interactions between Islamic scholars & Greek refugees led to translations of‬ ‭Creek texts into Arabic (eg. The Almagest)‬ -‭ ‬ ‭-‬ ‭ tolemaric model is of particular interest for predicting the sky‬ P ‭Greek star catalogs were translated using Arabic names and descriptions‬ ‭which persisted into modern times‬ ‭Early Renaissance Astronomy:‬ ‭-‬ ‭Renaissance = Rebirth in French‬ ‭13th C:‬ ‭-‬ ‭contact between Christian & Islamic scholars in Muslim Spain led to Latin translations‬ ‭of Arabic versions of Greek texts‬ ‭Regiomontanus (15th C):‬ ‭-‬ ‭produced the most readable & comprehensive Latin translation of The Almagest‬ ‭-‬ ‭the book led Christian scholars to adopt Aristotelian-Ptolemaic cosmology due to its‬ ‭consistency with Scripture‬ ‭ uridan (14th C):‬ B ‭- proposed new theories of motion which challenged Anstoreman theories‬ ‭- theorized that thrown/projected objects have impetus (in addition to their natural motion‬ ‭towards Earth)‬ ‭- therefore, if the Earth moves, projected objects inherit Earth's impetus‬ t‭ his showed:‬‭that‬‭a fixed Earth and a moving Earth‬‭appear equivalent from our perspective‬ ‭on Earth‬ ‭The Copernican Model‬ ‭Copernicus (16th C):‬ ‭●‬ ‭sought a truly CCM model that accurately matched observations and explained the‬ ‭connection between planets and the Sun‬ -‭ Earth has a daily spin about its polar axis (explains the daily motion of the sky)‬ ‭- Earth has an annual circular orbit around the Sun (explains Sun's annual cycle)‬ ‭- Earth's spin axis has a ~26,000-year circular wobble (explains the precession of the‬ ‭equinoxes)‬ -‭ retrograde motion is due to Earth‬ ‭overtaking another planet‬ -‭ brightness changes due to‬ ‭planets' varying distance from‬ ‭Earthsaturn‬ -‭ speed changes due to Earth’s‬ ‭varying viewing angle‬ ‭Copernicus' De Revolutionibus‬ I‭n the Copernican heliocentric model,‬‭Venus &‬ ‭Mercury are inner planets (explains their apparent‬ ‭proximity to Sun)‬ ‭ lso, the larger a planet's orbit, the longer its orbital‬ A ‭period (an appealing, orderly result)‬ ‭ he Copernican model publicly ridiculed by a few Christian scholars, but encouraged by‬ T ‭others‬ ‭Complete model published in "de Revolutionibus" (1543)‬ ‭●‬ ‭For the next ½ C, Copernican and Ptolemaic models were the two leading‬ ‭models of planetary motion‬ ‭The Early Observations of Tycho Brahe‬ ‭Tycho Brahe:‬‭late 16th C Danish astronomer‬ ‭●‬ ‭Sought a correct planetary model after identifying errors in the Ptolemaic &‬ ‭Copernican models‬ ‭●‬ ‭Observed that supernovae remain fixed relative to the stars (therefore, the star realm‬ ‭is‬‭not‬‭eternally unchanging)‬ ‭●‬ ‭Made the most accurate pre-telescopic records of planetary coordinates‬ ‭Tycho's Search for Stellar Parallax:‬ ‭Parallax:‬‭perceived shift of an object relative to‬‭its background due to the observer's motion‬ ‭●‬ ‭stellar parallax is proof of Earth's motion‬ ‭Even with the highest-precision instruments, Tycho couldn't detect stellar parallax‬ ‭●‬ ‭Therefore, either Earth is fixed or stars are > 1000s of AU from the Sun‬ ‭●‬ ‭Tycho concluded: Earth is fixed‬ ‭EXAM QUESTION: What is the Astronomical unit (AU)?‬ ‭●‬ ‭It is the average distance between the Earth and the Sun. 1 AU = 150 Million KM‬ ‭The Tychonic System‬ ‭Tychonic System:‬ ‭●‬ ‭Earth fixed at the center (geocentric)‬ ‭●‬ ‭The sun, Moon, and stars orbit Earth‬ ‭●‬ ‭planets orbit the Sun (heliocentric)‬ ‭ eometrically equivalent to the epicycle model‬ G ‭(therefore all features of apparent planetary motion‬ ‭are explained)‬ I‭nitial objections:‬‭"Crystal orbs" shouldn't intersect‬ ‭- Resolved by parallax distance of 1577 comet‬ ‭ y the early 1600s‬‭, the Tychonic System became the‬‭leading‬ B ‭geocentric model (Ptolemaic model discredited by Galileo)‬ ‭Kepler's "Cosmographic Mystery"‬ ‭●‬ F ‭ aced with declining income in Denmark,‬‭Tycho became‬‭the astrology to the King of‬ ‭Bohemia (Rudolph Il) in Prague‬ ‭Kepler:‬‭16-17C German mathematician‬ ‭●‬ ‭Initially believed: that spacing between planets is defined by a series of geometric‬ ‭shapes around the Sun‬ I‭n Cosmographic Mystery, Kepler proposed:‬‭that the‬‭5 Perfect Solids define the 5 spaces‬ ‭between the 6 planets‬ ‭●‬ K ‭ epler's heliocentrism was strengthened by the consistency between the Perfect‬ ‭Solids model & Copernican distances to planets‬ ‭Kepler's Search for the Driving Force of Planetary Motion‬ ‭ o avoid religious persecution, Kepler moved to Prague,‬‭where Lycho hired him to prove‬ T ‭the accuracy of the‬‭Tychonic System‬ ‭●‬ ‭This allowed Kepler to prove his own heliocentric model using Tycho's data‬ ‭ ate 16th C:‬‭Gilbert (English physicist) showed that‬‭Earth has a magnetic field like a bar‬ L ‭magnet‬ ‭ epler proposed:‬‭that if all celestial bodies are‬‭magnets, then the Sun's magnetic force‬ K ‭may be the cause of planetary motion‬ ‭Kepler's 1st and 2nd Laws of Planetary Motion‬ ‭• If planetary motion is driven by the Sun's magnetism:‬ ‭-‬ ‭Sun must be off-center, to explain its changing speed across the sky‬ ‭-‬ ‭Sun must therefore induce‬‭non-constant‬‭planetary speeds‬ ‭-‬ ‭In order for this model to make accurate predictions, planetary orbits must be‬ ‭elliptical‬ ‭ aving rejected the traditional notions of CCM, Kepler was led to his 1st and 2nd‬ H ‭Laws of planetary motion:‬ ‭1.‬ ‭1st Law:‬‭planetary orbits are ellipses with the Sun‬‭at one focus‬ ‭-‬ ‭the more elongated the ellipse, the greater its eccentricity‬ ‭-‬ ‭a circle is an empty win zero eccentricity‬ ‭2.‬ 2 ‭ nd Law:‬‭A planet's speed varies as it moves around‬‭its orbit; it‬‭moves fastest at‬ ‭perihelion‬‭and‬‭slowest at‬‭aphelion‬ ‭Kepler's 3rd Law of Planetary Motion‬ I‭n Harmony of the Worlds, Kepler showed: the‬ ‭spacing between planets correspond to‬ ‭harmonious music intervals‬‭(led to 3rd law)‬ ‭3.‬ 3 ‭ rd Law:‬‭A mathematical relationship‬ ‭between a planet's orbital radius and orbital‬ ‭period‬ ‭-‬ ‭the further a planet from the Sun, the slower its orbit‬ ‭ udolphine Tables:‬‭Kepler's tables of planetary coordinates,‬‭derived from his laws (most‬ R ‭accurate tables to date)‬