Transcript of Astro 201: Sept. 2, 2010 Do on-line practice quiz #2 (see d2l) Homework #2: posted on web page after...
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- Astro 201: Sept. 2, 2010 Do on-line practice quiz #2 (see d2l)
Homework #2: posted on web page after class Today: Ancient Greeks
Ptolemy V. Copernicus; retrograde motion Galileo Astronomical basis
for calendars Tycho, Kepler, Newton
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- Despite Aristarchus, for 2000 years, a GEOCENTRIC model of the
Universe was favored EARTH at the center STARS affixed to the
celestial sphere Moon, Planets and the Sun are between the EARTH
and STARS
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- PTOLEMY 90-168 AD Ptolemys ALMAGEST was translated into Latin
in 1496 GEOCENTRIC: Earth at center
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- Copernicus (1473-1543) Heliocentric Model: Sun at the
center
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- In order to understand the motion of the planets in the sky
Ptolemys model had to be modified In terms of the heliocentric
model, the planets orbit the Sun in ellipses, not circles
Retrograde motion of the planets with respect to the stars required
EPICYCLES Ptolemys Epicycles
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- Ecliptic the fact that the planets orbit the Sun in a plane
means that they always appear to lie on a great circle on the sky,
called the ecliptic
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- Retrograde motion The planets sometimes appear to be traveling
west to east, unlike the stars and Sun which always go east to west
Next slide: animation Astronomy Picture of the Day for Dec. 20,
2001. Jupiter and Saturn showing retrograde motion. Combining 23
pictures taken at 2 week intervals from June 2000 - May 2001.
Planet = wanderer
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- Ptolemys explanation for retrograde motion of the planets
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- Earth Equant Epicycle Deferent The planet moves along its
epicycle as the epicycle moves along the deferent around the Earth.
To make the observations as accurate as possible, it was necessary
to place the Earth slightly off center of the orbits, but to
preserve symmetry that meant that there was an equal place (Equant)
opposite the Earth from the center. The combined motion of the
planet and the resulting retrograde motion are shown. Earth Off
Center
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- Copernicus explanation for retrograde motion
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- Copernicus: On the Revolution of the Heavenly Spheres Published
at the time of his death, in 1543 Major Conclusions: 1.The planets
orbit the Sun 2. The apparent daily motion of the Sun and stars is
the result of the Earths rotation 3.The stars are much farther away
than the Sun
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- Heliocentric model: distance from Sun to stars must be much
greater than distance from Sun to Earth. Since Earth orbits Sun,
stars should show parallax (a shift in apparent position) over the
course of half a year.
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- Implication: distance to stars is several thousand times Earth
Sun distance. OBSERVATION: Parallax of stars is TOO SMALL to be
seen by the naked eye. Not observed until 1800s.
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- Parallax Unit of distance: the PARSEC A star which is one
parsec from Earth shows a parallax of one arcsecond Remember: 360
degrees in a circle, 60 arcminutes per degree, 60 arcseconds per
arcminute
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- Reactions to Copernicus : On March 5, 1616, Copernicus' work
was banned from being taught and discussed by the Congregation of
the Index "until corrected." It stayed on this list of prohibited
books and teachings until 1822. Martin Luther (1483-1546):
[Copernicus] is a fool who wishes to reverse the entire scheme of
astronomy; but sacred scripture tells us that Joshua commanded the
Earth to stand still, not the Sun. Giordano Bruno (1548-1600):
burned at the stake for advocating that stars are suns in their own
right, and that there is a plurality of worlds like the Earth.
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- v. 1.0 v. 2.0 v. 3.0 Cosmological Models: Version 1.0:
Superdome model Version 2.0: Geocentric model Version 3.0:
Heliocentric model
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- Which is right? Occam's Razor: Pluralitas non est ponenda sine
neccesitate "plurality should not be posited without necessity."
Given a set of otherwise equivalent models of a phenomenon, the
simplest one is the best. Keep it simple, stupid.
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- English philosopher from Ockham Franciscan Monk Got into
trouble with the Pope for advocating apostolic poverty Died of the
Black Death while in exile Advocated Epistomological Parsimony c.f.
Ontological parsimony Epistomology = theory of knowledge Ontology =
what exists? William of Occam 1285-1349
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- 1610 Siderius Nuncius (The Starry Messenger) Spots on the Sun;
the Sun rotates The Moon has mountains, craters, rocky surface with
imperfections The planet Jupiter is not a pinpoint star but a disc
in the sky WITH MOONS that orbit it Venus has PHASES like the MOON
Galileo Galilei (1564 1642) Italian First to use a telescope to
look at the sky
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- Spots on the Sun The Sun rotates Eventually went blind Galileo
Galilei (1564 1642)
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- The Moon Has Mountains and Valleys Galileo Galilei (1564
1642)
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- Phases of Venus Galileo observed that Venus showed phases
entirely like those of the moon from full to crescent, which it
must do if the Copernican theory was correct. According to the
Ptolemaic theory Venus would have to be a perpetual crescent.
Galileo Galilei (1564 1642)
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- Observations consistent with Copernicus, inconsistent with
Ptolemy.
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- Jupiter Has Moons Galileo Galilei (1564 1642) Galilean Moons 4
Largest moons of Jupiter Io, Europa, Callisto, & Ganymede
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- 1632: "Dialogo Dei Massimi Sistemi Dialogue on the Two Chief
World Systems In Italian, Not Latin -- For the common people Two
people, one representing the view of Ptolemy and other the view of
Copernicus, present their arguments before an intelligent layman.
Galileo Galilei (1564 1642) "Eppur Si Muove "(And, yet it moves!")
The Pope Urban II thought that Simplico, the character who upheld
the views of Ptolemy in the book, was a deliberate and insulting
caricature of himself 1633: Trial by Church (threatened with
instruments of torture), forced to recant views
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- 1633: Galileo is ordered to his house in Arcetri, under house
arrest, where he remains for the rest of his life. The book
remained on the index of forbidden books until 1822 Pope John Paul
II finally gave an address that admitted that there had been errors
in the treatment of Galileo by the church, in 1992. ASIDE: Contrast
Galileo with Nicolas Steno (1638-1686), who laid the groundwork for
the interpretation of the fossil record. See The Seashell on the
Mountaintop by Alan Cutler.
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- Modern Scientific Method 1. Observations and Experiments Data
which describes the physical world 2. Theory, Hypotheses, Models:
-> Organize Facts from experiment & observations Unifying
principles Make testable predictions
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- Creationism and Intelligent Design vs. Evolution. The example
of gravity as a scientific theory: Newtons Law c. 1700 AD Einsteins
theory of General Relativity c. 1916 Photon versus wave description
of light The most interesting scientific questions to work on for a
professional scientist are those we don't know the answer to.
Interesting theories to work on are those which fail to explain an
observation or fact. Many modern astronomers are deeply religious
people.