Download Astronomy 104: Stellar Astronomy

Astronomy 104:
Stellar Astronomy
Lecture 4: Science and our Understanding
of the Universe (Continued)
Spring Semester 2013
Dr. Matt Craig
Monday, January 28, 13
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For next time:
• Bring Lecture-Tutorials for Introductory
Astronomy.
• Chapter 3, Sections 2-4
• Reminder:
• Do your moodle assignments, due EVERY
Friday.
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Objectives
•Describe Galileo’s observations (3-3).
•Explain why Galileo’s observation of the
phases of Venus demonstrated that the
geocentric model was incorrect (and do the
same for his observation that Jupiter has
moons) (3-3)
•Describe Copernicus’ heliocentric model (3-2)
•Explain why Copernicus’ heliocentric model
wasn’t accepted immediately (3-2)
•Describe Tycho’s contribution to the discovery
of the correct description of the Solar System.
(3-4)
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Explaining Motions of Planets:
two broad ideas
Geocentric: Earth
at center
center
Heliocentric:
Sun at
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Ptolemy’s Geocentric Theory (Animation)
Mars’ Orbit in Geocentric Theory (simplified)
• Says planets
moved on
circular paths
nested on
circular orbits to
describe the
motions of the
planets.
O = Earth
P = Mars
Yellow Dot = Sun
• Complicated...
but accurate
enough to match
available
observations..
http://people.scs.fsu.edu/~dduke/models
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Copernicus' Heliocentric Model (Animation)
Mars’ Orbit in Heliocentric Model (Simplified)
• Just have a few
circles centered on
the Sun.
• Unfortunately...
O = Earth
P = Mars
Yellow Dot = Sun
doesn’t
simplify
calculations
much.
• As accurate as
Greek Geocentric
Theory, BUT NOT
MORE
ACCURATE.
http://people.scs.fsu.edu/~dduke/models
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So why didn’t Copernicus’ Model take off...
• Computations almost as
tedious... (no real savings)
• Copernicus’ model wasn’t
any better or worse than a
Geocentric theory at
predicting positions of
planets, as far as observers
then could tell.
• KEY POINT: What was
needed were predictions that
would distinguish this model
from the Geocentric Theory.
We're stuck, since no test can distinguish
between the two models/theories!!!
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Direct Comparison: Motion of Venus
Heliocentric
(Sun-Centered)
Geocentric
(Earth-Centered)
Notice in both cases Venus (P) as seen from Earth (O) never appears to be far
from Sun (Yellow dot).
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Turning a Heliocentric Model into
a Theory
• Galileo Galilei uses a
telescope to look at the
sky (he did not invent it).
• Laid the groundwork for
a better understanding of
physics
• He looked at Venus and
noticed its phases...
Galileo Galilei (1564 - 1642)
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Lecture Tutorial
• Please get together with your neighbor
and work on the "Testing a Scientific
Theory, Part 2".
• Rules:
• You must work in groups of at least 2 and no
more than 4.
• You must come to an agreement on all answers
BEFORE writing them down.
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OK.... And????
• Do you want to know what Galileo
actually saw for the phases of Venus?
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Observed phases of Venus
Image credit: Chris Proctor, Torbay Astronomical Society
http://www.halien.net/TAS/index.htm
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Galileo’s Observations
The Moons of Jupiter
The Sky is Full of Faint Stars
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Mountains on the Moon
Sunspots on June 23 1612.
The Phases of Venus
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Galileo’s observations
1.Phases of Venus
2.Moons of Jupiter
• Observed four moons of Jupiter
• Like a “mini-solar system”
3.Discovered that sun rotates about once per month
by observing sunspots
4.Moon has mountains and valleys, like Earth
• Suggests other bodies in solar system are like
Earth
5.Found that the Milky Way is composed of
many, many individual stars
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Let’s try those clickers!
•Turn it on.
•If your clicker doesn't connect, you may need to
configure your clicker (only need to do this once)
•Press and hold on/off button for two seconds.
•Press A, then A.
•Register your iClickers following the
instructions on the back of the remote. If
you forget to do this before the end of
the semester, you will not get credit for
your participation in this class.
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McQuestion
• Which of the following statements would
you say is most correct about Galileo's
observations.
(A)Galileo proved the heliocentric model of the
solar system is correct.
(B)Galileo proved the geocentric model of the
solar system is incorrect.
(C)Both (A) and (B).
(D)Neither (A) or (B) since you can't "prove" the
truth of a theory in science!
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"Not right" doesn’t necessarily
mean "completely wrong"
• Copernicus’ heliocentric (sun-centered)
model was no more accurate than the
Greek geocentric (Earth-centered) model
• By the time Galileo whipped out his
telescope, observations showed both
models inaccurately predicted planetary
positions.
• Do observations contradicting predictions of
your model mean you have to toss out the
entire model?
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Aside: a “hybrid” model
Earth
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Tycho Brahe:
The Bad Boy of Astronomy
• Made very accurate
observations
• Didn’t think heliocentric
model was right since no
parallax of stars observed.
Tycho Brahe (1546-1601 CE)
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For next time:
• Bring Lecture-Tutorials for Introductory
Astronomy.
• Chapter 3, Sections 2-4
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