NATS1745 - chapter 3
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According to the textbook, what was it
about Ancient Greece that enabled its philosophers to theorize about why the
sky moves the way it does, as opposed to just using it for tracking time and
• Greece was broken up into innumerable valleys and islands. There could be no over-arching control system. Instead, each region developed its small own city state, or polis, the Greek word that gives rise to ‘politics.’ And trade between the city states was in the hands of independent merchants. So Greece developed the world’s first middle class culture. With fluid funds, the prosperous Greek middle class had time on their hands - and freedom to do what they liked with it. The fundamental geography and decentralized rule of Ancient Greece allowed for an intellectual freedom that led to a revolution in scientific thought
Why is Thales called the "Father of
Science"? According to legend, what celestial event did he successfully
predict in order to prove his philosophy?
- Considered the "Father of
- Science" for attempting to find explanations for natural phenomena that
- didn't involve the gods. Thales apparently made the first accurate prediction
- of a total eclipse of the Sun, on May 28, 585 BC.
did Anaximander believe about the Earth?
- Set the Earth afloat in
- air. He described how the earth, moon,
- sun and stars are organized stars. He set the earth afloat-> meaning that he
- proposed that we are not standing on a ground that stands infinitely beneath
- on. We are standing on a disk in space.
What was Pythagoras proposing when he
called the Universe a "cosmos"? What did he propose about the shape
of planetary orbits?
- According to legend, when he
- discovered that musical pitch is determined by the length of the instrument, he
- realized : the Universe is a cosmos ( a harmonious system that obeys knowable
- He taught that all celestial
- motion is perfectly circular, and that the Earth is a sphere
proposed that the Earth is round? Describe 3 observations that suggest this
- Pythagoras proposed that the
- Earth is round.
- Ships gradually disappear on
- the horizon bottom – first
- Earth's shadow on the eclipsed
- moon is always round
- When you travel North or South,
- the constellations rise and set more rapidly than they would if Earth was flat
What did Philolaus believe about the Earth?
What did this belief explain about the sky?
- He believed that the earth
- explains why all celestial
- bodies rise and set
- no need to say that the moon has a monthly
- component and a daily motion, as well as the sun
- the movement of celestial bodies becomes far
- less complex
- earth rotates once a day : but Philolaus
- thought the earth moves through space once a day
- according to him, the central fire is never
- his argument for that was that only one side
- of the earth is inhabited
- and that side never faces the fire
- Philolaus also proposed that between earth
- and central fire there is anti earth ( never seen ) and the purpose of it was as a protective shield
What did Herakleides believe about the
- He set Earth spinning daily
- around its own axis. He had all the planets orbit around the earth as well.
did Herakleides believe about the motion of Mercury and Venus, and why?
- He placed Mercury and Venus in
- orbit around the Sun to explain the Sun - centered appearance of their motion
- and their brightness changes
observation allowed Aristarchus to estimate the size of the Moon?
- Aristarchus used Earth's shadow
- on the eclipsed moon to measure the Moon's size relative to Earth's.
measurement in the sky allowed him to estimate the distance of the Sun compared
to the Moon's distance?
- Used the angle in the sky
- between the Sun and quarter Moon to measure the Sun's distance and size
- relative to the Moon's
Combining these results, what did he
correctly conclude about the relative sizes of the Sun, Moon and Earth (i.e.,
which is biggest, smallest, etc.)?
- His measurements weren't
- accurate, but he correctly deduced : the Sun is much larger than Earth, and
- Earth is larger than the Moon
did this conclusion lead Aristarchus to propose about the known Universe?
- This led him to propose a
- heliocentric model of the Universe, with only the Moon in orbit around Earth (
- owing to the Moon's straight night - to
- - night path around the sky)
direction do planets normally move across the sky from night to night? In what
direction is a planet moving when it exhibits retrograde motion?
- Planets display both direct (
- forward )motion ( W to E ) and retrograde ( backward) motion ( E to W).
Does a planet's apparent motion appear constant or non-constant in speed, as
seen from Earth? What about a planet's brightness?
- From Earth the speed of the
- planets look non-constant is what we see
- The brightness also looks
belief of Plato's directed the objectives of the next generations of Ancient
- All celestial bodies are
- perfect unblemished sphere
According to Eudoxus, what do the planets reside on in space?
· All celestial bodies are perfect unblemished sphere
· Constant motions
did Eudoxus propose that each planet is carried around Earth by two
- Came up with double sphere
- model to try and explain
. In Aristotle's cosmology, what body is at
the centre, and what is everything on this body composed of? What is everything
outside of this body composed of? What are the qualities of this material?
- Made of ether quintessence
- The Earth is fixed at the
- centre of the Universe ( geocentric).
- All matter in the terrestrial realm is composed of four elements :
- Earth, water, air and fire.
What model did Aristotle use to explain the
motion of the planets? In this model, what are the shapes of the planetary
orbits, and do the planets have constant or non-constant speed through space?
- They are circular all the
- crystal orbs are spheres
- They have constant speed
- through space
did Aristotle explain the daily motion of the sky?
- He said [ believed earth is
- fixed] surrounding our entire universe is one enormous crystal orb that [spins
- once a day,], and it explains why the sun rises and sets everyday.
What was Aristotle’s explanation for the
source of all motion in the Universe?
- Prime mover that constantly
- pushes on us
did Aristotle believe that comets are atmospheric phenomena?
- Aristotle taught comets must be
- atmospheric phenomena because they don't appear eternal, therefore they can't
- be celestial bodies.
. Describe the components of Appolonius'
epicycle model. Where is the Earth in this model? Is all motion constant and
circular in this model?
- Appolonius upgraded the Eudoxan
- planetary model to the epicycle model.
- The model still required that the planets still have constant circular
- motion around fixed earth, but he was able to come up with a new way that
- involved the movement of the planets.
- All motion is circular and with constant speed. Deferent circle, planet,
- earth, epicycle. All motion is circular and constant.
does Appolonius' epicycle model explain the 3 features of planetary motion?
- Changing speeds of the planets
- in the sky- the motion cancels out so slower
- The changing brightness of the
- planets in the sky- when a planet goes retrograde it is at is closest position
- to Earth at the bottom therefore brighter
- And retrograde motion – is that
- when the planet comes around the bottom of the epicycle them motion is opposite
- to the direction of the epicycle
What measurement is Eratosthenes famous
for? What tool did he use to obtain his result, and what did he physically
measure with this tool?
- Meaused the circumference of
- the Earth
- Measured the length of the
Which feature of the Antikythera Mechanism
suggests that it was constructed to predict the motion of the celestial bodies
using Hipparchus' model?
- Hipparchus checked out the
- Moon’s motion in extraordinary detail, which meant he could predict eclipses
- with more confidence than anyone before him.
- The complicated gearing of the Antikythera Mechanism even mimics the way
- the Moon’s speed changes over a cycle that lasts nice years. The way in which it displayed the moon is
- very advances, and seems to be based on a theory of the Moon developed by
What observation led Hipparchus to discover
the precession of the equinoxes? How does precession effect the Sun? How does
precession effect the stars? How does precession effect your zodiac sign?
- Observed the 20 minute
- difference between time between the solstices
- Causes the suns position in the
- sky to shift by a tiny amount by year to year
- Zodiac signs are different than
- in the past because the Sun's position relative to the constellations changes.
Explain briefly how it was determined that
the Farnese status of Atlas is holding a celestial globe constructed from
Hipparchus' lost star catalogue.
- A Roman statue of Atlas carries
- a copy of Hipparchus’ Farnese globe - his incredibly accurate star catalogue -
- on his shoulders. Brad Schaefer, a astrophysicist and historian holidaying in
- Italy, stumbled across the globe in the National Archeological Museum in Napes.
- He has dated the original to around 125 BC - contemporary with the time when
- Hipparchus lived. The only astronomer
- who was mapping the stars at the time was Hipparchus.
What was the name of the definitive
Astronomy textbook written in roughly 150 AD, and who wrote it?
- Ptolemy drew together all of
- the Greeks’ knowledge of the heavens in a 13-volume masterpiece called the
- Matematike Syntaxis [ Mathematical Treatise], better known today by its later
- Arabic title, the Almagest.
If we could observe a planet's motion from
the equant point, would its apparent speed be constant or non-constant? How
does the equant point conflict with the Aristotelian view of planetary motion?
- It would be constant that is
- the definition of the equant point
- Conflict is that the equant
- point forces a planet to speed up and slow down
- Speed up when far from equant
- point slow down when close to equant point
Why did Ptolemy establish 2 different rules
which attach the motion of the planets to the Sun?
- to explain why mercury and
- venus always appear close to the sun in the sky, while the other planets don't
is the one mistake in Ptolemy’s order of the planets? What wrong assumption
about space led Ptolemy to underestimate the size of our visible solar system
(i.e. out to Saturn)?
- Ptolemy placed the planets in
- order of their decreasing apparent speed. The order of the planets was correct,
- but the Sun and Earth were incorrectly switched
- By assuming no space between adjacent orbits,
- Ptolemy estimated the " Universe's size to be ~ 20,000 Earth radii (
- actual 260,000). Despite the error, this proved the enormous distance to the
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