Lecture 4 Flashcards
who created the earliest systematic, quantitive, physical model of the universe and what was it
Anaximander, earth as a cylinder suspended in a void of space, sun and moon as hollow rings filled with fire with holes
who created the first mathematical model of the world and what was it
Eudoxus of cnidus, series of geocentric celestial spheres, made of quintessence, not clear if regarded this as a literal physical model or a calculation tool
what is retrograde motion
planets gradually move across the sky compared to the stars
typically east but reverse direction west every 2-24 months for 21-180 days
what is eudoxus’ principles
earth is centre of universe
celestial motion is circular and uniform
centre of the path of any celestial motion is the same as the centre of its motion
the centre of all celestial motion is the centre of the universe
what are the specific spheres for eudoxus’ model
sphere 1 gives the night/day cycle
sphere 2 gives the annual cycle
sphere 3 rotates about axis through sphere 2 equator
sphere 4 tilted from sphere 3 and rotates with the same period in opposite direction
3 and 4 allow retrograde motion
what model came after eudoxus’
Apollonius of perga and Hipparchus developed the epicycle-deferent model due to eudoxus model becoming obsolete from observations
the model retained circular motion but no longer purely around earth
what did ptolemy do
combined and refined earlier observations and epicycle models into a coherent and accurate system
what data did ptolemy collect
times of equinoxes, times when planets rise and set on different dates, dates and times of lunar and solar eclipses, shadow on the moon during a lunar eclipse
what is ptolemys model from the data he collected
earth isn’t at the centre, there is an epicycle, a big circle Called the deferent is what the epicycle moves around, eccentric is centre of deferent, equant is the epicycle centre, planet moves along epicycle (put on sheet)
ptolemy in comparison to what we now know
epicycle is equivalent to earth not being at the centre of eccentric is equivalent to orbits not being circular
equant equivalent to speed around sun not being constant
what did ptolemy think of earth rotating or moves
he acknowledges that celestial phenomena are consistent with it, missing concept of intertia made him reject it
what did aryabhata do
discussed rotation of earth and made clear statement of relativity of motion in astronomical context, worked on variants of ptolemys model
what did abd al-rahman al -suifi do
wrote book of fixed stars, first recorded observation of Andromeda
what did su song do
oldest surviving prints star catalog, designed Kaifeng astronomical clock
what did ulugh beg do
measured length of the year within 25s
created Zij-i sultani, sultans star catalogue
most accurate star list of its time
what did somayaji do
compilation of the system
said other planets orbit the sun
sun orbits earth
mathematically close to heliocentric model
what is the Copernicus model
sun explicitly in the centre
based partly on new measurements, partly on old
main motivation was disliking ptolemy’s equates as believed in purely central circular motion
model isn’t much accurate
what is the core Copernican idea
distance from earth to sun is tiny in comparison with the distance to the stars, now know this to be very true
