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SYRACUSE / Astronomy / ASTR 101 / How do object move?

How do object move?

How do object move?


School: Syracuse University
Department: Astronomy
Course: Our Corner of the Universe
Professor: C. armendariz-picon
Term: Fall 2015
Tags: astronomy, AST101, SUAST101, Science, Syracuse University, syracuse, Johannes Kepler, newton, Einstein, Tycho Brache, TychoBrahe, Nicholas Copernicus, Copernican Universe, copernicus, galileo, and Galileo Galilei
Cost: 25
Name: AST 101, Week 5 Notes
Description: These notes describe the history and the evolution of the models of our universe, including facts about the scientists needed to know for the exam.
Uploaded: 10/17/2016
10 Pages 183 Views 5 Unlocks

September 27, 2016

How do object move?

AST 101: Professor Freeman (and guest lecturer)

Lecture: Modeling the Universe (guest lecture)

Textbook Pages: 54-61

Lecture Tutorial: None

∙ Key Questions

o How has astronomy changed?

o How has the way we have viewed our place in the universe changed?

o How has people’s view of science changed over time?

▪ Covering 350 BCE – 2000 CE

▪ Contribution of major figures

∙ Aristotle  

o Greek philosopher born 384 BCE in Macedonia (North Greece) If you want to learn more check out How many elements are there in 2^a, if there are n elements in a?

o Made major contributions in many things

o Especially “physics”

What is stellar parallax?

o Why do things move the way they do? We also discuss several other topics like What is ancient aegean?

o Everything needs to be logically deduced

▪ Obvious observations followed to logical result

▪ Close observation not necessary, even contradictory

o How do things move?

▪ Things had a “natural place”

▪ Rocks at center of earth, fire in heavens

▪ Everything outside of Earth was perfect and immutable

▪ Everything had to be quantified

▪ Celestial spheres; one for each planet, stars in background, earth in center ∙ This doesn’t work

∙ What goes wrong?

What makes nicolaus copernicus a significant figure in history?

o Planets move backwards in the sky sometimes!

o Retrograde motion

o Things a model needs

▪ Explain retrograde motion

▪ Changing speeds of planets

▪ Phases of moon, inner planets

▪ Why is there no stellar parallax?  

∙ The change in relative position of star due to earth’s motion

∙ Relies on the fact that stars are not all the same distance away Don't forget about the age old question of Why was the free soil party created?

▪ Who can fix this?

∙ Ptolemy

o Greco-Egyptian born 100 CE

o Famous for mapmaking and astronomy

o A brief aside

▪ The Earth is round.

▪ Ptolemy knew.

▪ People before him knew.

▪ People knew for a long time after.

▪ Columbus was a bad mathematician, which is why nobody listened to him. ▪ Now back to astronomy.

o Ptolomaic Model

▪ Added epicycles – an extra sphere each planet was on

▪ Also added equant, which offsets the orbit a bit so the planets move faster at  different times Don't forget about the age old question of Are upside and strategic risks synonymous to each other?

o Does this work?

▪ Yes!

▪ Could predict where stars would be almost perfectly, even worked thousands of  years after it was designed

o What does this do to the planets?

▪ Planets now make large flower patterns in the heavens

▪ Who would have thought this actually worked?

o The main issue is, people thought about astronomy was two distinct, different fields: ▪ Astronomy

▪ Natural philosophy

∙ Medieval astronomy

o Predict where stars were

o Basically math’ crunched numbers and weren’t too concerned if how they did their  calculations related to the real world

∙ Natural philosophy

o Ones asking how, why

o Aristotelian logicians

o Thought of heavens as outside their scope, essentially inexplicable

o No equations, no math, looked down upon

o Math was about “the perfect”, not applicable to the world around us, not “the language  of the universe” Don't forget about the age old question of Why are social contract important in large societies?

∙ What changed? We also discuss several other topics like Which of the following characteristics of jurisprudence is false?

∙ The Islamic Golden Age

o During European “dark ages”; 11th-14th centuries

o Helped hold onto classical knowledge

o Saw issues with Ptolemy’s calculations

o Began introducing their own, finer models, though not completely advocating for new  models

o These ideas began to trickle into the West, sparking the Renaissance

o New influx of knowledge, numerous revolutions will occur

∙ Copernicus

o Nicolaus Copernicus (1473-1543), Polish

o Trying to improve upon the Ptolemaic model

o Had a lot of (personal) issues with it

o Copernican Model

▪ Planets orbit the Sun in circles

▪ Got rid of equant

▪ Now explained retrograde motion

▪ Stars immobile

o People didn’t fully get on board

▪ Published posthumously w/editorial note: in essence, “This is weird, don’t  worry, he’s just an astronomer, so this is just math and has no basis in reality” o Didn’t help improve calculations

o Not simpler- theory more complicated and was worse at explaining what everyone saw o Within 60 years and after his death, “maybe 15 people believed him”.  

∙ Galileo Galilei

o 1564-1642 in Pisa

o First person to receive joint degree of mathematics and natural philosopher at U Pisa o Did many things

o Made his own telescope, looked at sky

o Discovered moons of Saturn

o Found mountains on the moon, craters

o Contradicted idea that all things in the heavens were perfect and that they orbited Earth o More issues with spheres

▪ Showed that comets were not in the atmosphere

▪ Passed between planets

▪ All objects fall at the same rate

▪ Possibly a lead in what others will do

o Church’s involvement with work and views, mostly political issues

∙ Tycho Brahe

o 1546-1601, Denmark

o Uraniborg – had an observatory

o Contemporary of Galileo  

o Brache’s Model

▪ Sun, moon, and stars orbited Earth

▪ Everything else orbits the Sun

▪ Adopted by Catholic Church as it explained a lot

o Multiple models exist at the same time?

▪ What’s the benefit?

▪ Both explain planetary motions

▪ Copernican model needed the stars to be essentially infinitely away

▪ Brache’s model agreed more with the accepted views of how the universe  worked

▪ Both heavily influenced by observation

▪ Both began making statements about how the universe worked

∙ Johannes Kepler

o 1571-1630, Denmark

o Student of Brache’s

o Big advocate on harmony

o Produced own model of the solar system, guided by Kepler’s Laws

▪ Replaced circles with ellipses

▪ Trying to find harmony of planets

▪ Didn’t know how everything worked but he did a good job

∙ Isaac Newton

o 1642-1726 England

o Another person who contributed to many fields: math, physics, astronomy, alchemy,  and more

o Principia Mathematica

o Where things were

▪ Heliocentric models made great predictions but were less widely accepted ▪ But there was no understanding why

▪ Geocentric models had issues but were established in years of natural  


∙ Gravity

o Everything in the universe attracts everything else in the universe

o Planets stay in motion around sun (which is huge)

o Calculations regarding the moon were able to predict motion exactly

o We now know why the heliocentric model works

∙ What’s the change?

o Gravity sounds a lot like previous theories

o The difference is that now, everything in the universe is under the same laws. o Heavens no longer objects we cannot understand

o Things true on Earth are true everywhere in the Universe

o Newton was a part of how we viewed math as contribution to theories regarding nature o Tried to explain motions using equations and geometry, not helpful

o So he invented calculous to understand motions

o Math was an inescapable part of the discovery

∙ There are still issues, however.

o Gravity is weird

▪ Acts in infinite distances

▪ Instantaneously, without anything needed it

▪ Feels like magic

∙ Demonstrative of fundamental shift in how natural philosophy and science was viewed o You make observations

o You make a prediction

o Test that prediction

o Inactively applied it to rest of world

o Scientific method!

∙ How does gravity work?

o Baffling, but it worked

o Descartes – vertices

▪ Winds of ether blew planets around

∙ Scientific model

o Everything in solar system seemed exposed

∙ More issues

o Mercury’s orbit was weird, discovered a planet “inside” of Mercury, Vulcan  (“discovered” in 1859, though it isn’t there

∙ Albert Einstein

o One last fix

o 1879-1959 Germany/US

o Theory of relativity

o “bedsheets of space” with valleys, fixed issues, gravitational waves

∙ Present Day

o Everything by laws of motion: Newton’s or Einstein’s (or Kepler’s)

o Math as guiding principle/ “language of universe”

∙ Things are still broken

o Still a bit off (especially in terms of galaxies)

o Led to the prediction of dark matter

▪ Sounds a bit familiar: we trust in a theory, can’t possibly be wrong, so it has to  be something we can’t see

▪ Dark matter could be a thing, but…

o So could Modified Newtonian Dynamics

▪ No dark matter, but our understanding of how motion works is a bit off ∙ Has the field changed?

o Problem types haven’t, nor have types of solutions

o But, it has in how we guide our problem solving and how much we can trust ways of  knowing

o Not better, but different

September 29, 2016

AST 101: Professor Freeman

Lecture: From Ptolemy to Kepler

Textbook Pages: 61-65

Lecture Tutorials: None

∙ Grravity from Newton to Einstein (interlude)

o Newton’s space and time are absolute, independent of each other

o We can measure points in space and time with variables x, y, and z

o Newton’s gravity is a force

▪ We can learn how strong a force it is with measurement

o Then Einstein comes along

▪ Space and time are intertwined: different manifestations of the same thing ▪ Universe is made of spacetime

o Einstein’s gravity is a curvature in spacetime

▪ Influencing definition of “straight”

▪ Spacetime has been bent by presence of earth

▪ More mass? More curvature

o “Waves” in spacetime?

▪ Shaking an object inside air makes soundwaves

▪ A computer “shakes” electricity to make electromagnetic waves to “talk” to the  wifi

▪ If one shakes gravity back and forth, there will be waves

∙ Like if two stars orbit each other

o What would it look like?

▪ A person being squeezed and stretched

▪ However, spacetime is stiff; one would need a huge mass

▪ Imagine a neutron star (the densest thing in the universe); the corpse of a dead  star; even despite this, you’d be squeezed smaller than the radius of a proton

o Indirect Detection (Hulse and Taylor)

▪ Observed 2 neutron stars orbiting each one

∙ Saw energy went away/was being lost

∙ Nobel Prize Winner 1993

o LIGO; Direct Detection

▪ We can use waves of light

∙ Interferometer: uses waves exactly in sync, shining on top of each other  

to measure differences to the preciseness of a billionth of a meter

▪ Syracuse University Gravitational Wave Group

∙ A billionth of a trillionth of a gravity wave was found

∙ But, they were found!

∙ GW150914

o Two black holes merging

▪ Every other way we have to observe the universe/the heavens is from observing  light they emit

∙ Colors too

∙ Gravitational waves provide a new way of looking at things

▪ How is relativity true?

∙ Exhibits change a smidgen, are not stagnant

∙ From Ptolemy to Kepler

o Casually mixed ancient and modern

▪ Earth at center, sun at center

▪ How did shift happen?

▪ How is this part of emergence of modern science?

▪ What else can we learn in the process?

o Greek philosophy

▪ We can understand nature, proposed natural causes for phenomena

▪ proposed models for things in nature

▪ used mathematics in these models

▪ recognized that any model had to agree with observation

▪ Believed in the transcendent Truth and Beauty of mathetmatical perfection ▪ “Circles are the most perfect shape, thus things in the sky must go in circles” ▪ Recognized that any model had to agree with observation

▪ Increasingly saw astronomy as separate field from natural philosophy

Natural philosophy


Concerned with fundamental Truth  of things

Concerned with predicting the  motions of stars and planets

Very concerned with logic, for  instance

Not all that concerned with the  transcendent Truth of their models

Saw the heavens as mostly outside  their purview

“…but do we get the right answer?”

Figuring out where the planets are is  grunt work!

Known mostly from Ptolemy’s  Almagest

∙ Ptolemy and his model

o Lived in Alexandria, Egypt, the center of scholarship in that part of the world o Astronomer

o Almagest

o Everything is attached to crystal spheres which spin in a uniform, perfect way around  the Earth

▪ Well, sort of, the Earth isn’t quite at the center of the planet-spheres

▪ Well, sort of, they don’t turn quite uniformly, but with a fudge that keeps the  perfection of “circles”

▪ Epicycles

∙ The center of the epicycle rotates not-quite-uniformly about a point  

not-quite-at-Earth, and then the planet rotates in a circle along the  


∙ Astonishingly precise, though way too complicated and fudgy

∙ Muslims studied the Greek writing after the Library at Alexandria was burned, and accumulated  knowledge about the motions of the sky; naming many stars, refining Ptolemy’s model, and  made enormous strides in mathematics

∙ Europe didn’t have much of a natural-philosophic or scientific tradition from the fall of Roman  Empire to c. 1400

o Ptolemaic model known, but mostly just applied

∙ Copernicus

o Proposed that, instead, everything orders the Sun in perfect circles

▪ Ptolemy’s model was geocentric

▪ Copernicus’ model was heliocentric

o However, Copernicus’ model was actually less precise than Ptolemy’s

∙ Galileo Galilei

o Perfected the telescope

o Noticed there were things orbiting Jupiter!

▪ If things orbit Jupiter, then not everything orbits the Earth! We are not the  center of everything!

▪ This was a huge shakeup – to philosophy and to religion

o The “Galileo Affair”

▪ Galileo published what he saw with his telescope in 1610.

▪ He argued that the moons of Jupiter, along with the phases of Venus, proved  the Earth moved. Now Galileo has left astronomy--predicting things--entered  philosophy!

▪ Something else happened between Copernicus and Galileo: the Protestant  Reformation and the Counter-Reformation!

▪ This meant that the Church had gotten a bit touchy about theology and heresy. o In 1616 the Church declared heliocentrism heretical

▪ In 1632 Galileo published a popular book, Dialogue Concerning the Two Chief  World Systems, defending heliocentrism

o In 1633 the Inquisition declared him a heretic, banned all his books, and sentenced him  to house arrest until he died in 1642.

o The Church un-banned his books and heliocentrism in 1835.

(Ancient) Astronomy


Predicts the motion of things

Concerned with understanding the nature of things in the sky

Not that concerned with their nature

“What are they and by what rules do they  operate?”

An exercise in calculation

Predict their motion by understanding  their nature

∙ Additional

o Ptolemaic model, courtesy galileo.rice.edu

o Copernican model, courtesy Wikimedia Commons ▪

o Galileo’s model, courtesy britannica.com

o Kepler Model, courtesy cloudfront.net

o Newton vs. Einstein, courtesy weebly.com ▪

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