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Pull out a ½ sheet or use the back of your old quiz Weekly Schedule Today
•  Hw # 2 due •  Quiz # 2 •  Geocentric vs. Heliocentric models •  Kepler’s Laws –  Astronomy InteracGves •  Newton and Gravity –  Lecture tutorials Thursday •  ElectromagneGc spectrum –  Lecture Tutorials •  Lab # 3-­‐ Spectral Analysis Lab Geocentric model (Earth centered) Retrograde motion of
planets
Favored by: Aristotle, Ptolemy, and
others
Planets:
•  Move with respect to fixed stars
•  Change in brightness
•  Change speed
•  Have retrograde motion- eastward
•  Are difficult to describe in earthcentered system
Ptolemy's retrograde model
Heliocentric model (Sun-­‐centered) Copernican system Explains retrograde motion,
Galileo’s observations
Fashioned by: Copernicus,
Galileo, Brahe, Kepler
Mars' actual motion
Venus' retrograde motion
Galileo’s observations support the
Heliocentric Model
•  Your group should select what it believes to be Galileo’single most important astronomical observaGon. Explain what he observed using sketches and why it was most important. (See pages 29-­‐30 in your book) Observations of Galileo:
•  The Moon has mountains, valleys, and craters.
•  The Sun has imperfections, and it rotates.
•  Jupiter has moons.
•  Venus has phases.
All these were in contradiction to the general
belief that the heavens were constant and
immutable.
Direct conflict with church, made to retract
claims under threat of torture, house arrest
1616-1633
Church publicly apologized in 1992!!!
Kepler’s Laws-­‐ based on Copernican's model •  1st: Planets have EllipGcal orbits not circular orbits with the sun at one focus drawing_ellipse_with_string
Kepler’s Laws •  2nd Law: Equal areas over equal Gmes *Planets move faster closer to Sun
Kepler's 2nd Law
During which part of the planet’s orbit would the planet move with the greatest speed? A.  A B.  B C.  C D.  D 10
Kepler’s Laws •  3rd Law: p2 = d3 –  Square of period of planet’s orbital mo6on is propor6onal to cube of semimajor axis. *Planets further away from Sun have
longer periods
Astronomical unit (AU)
Average distance
between Earth and Sun
If a small weather satellite and the large InternaGonal Space StaGon are orbiGng Earth at the same alGtude above Earth’s surface, which object takes longer to orbit once around Earth? A.  A) The large space staGon B.  B) The small weather satellite C.  C) They would take the same Gme What would happen if Mercury and Jupiter were to switch places in their orbits around the sun? A.  Jupiter would have a shorter orbital period than before B.  Mercury would have a shorter orbital period than before C.  Neither of the two planets would have any change in their orbital periods Imagine a newly discovered planet is 3 AU from the Sun. Which of the following best approximates the orbital period of this planet? A.  1 year B.  3 years C.  5 years D.  9 years Choose your answer below (Class Ac)on: Eccentricity of Shapes, Kepler’s 2nd Law, Kepler’s 3rd Law) 25%
25%
!D
25%
!C
http://astro.unl.edu/classaction/
questionsList.html
25%
!B
A B C D !A
1. 
2. 
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Consider a planet orbiGng the Sun. If the mass of the planet doubled but the planet stayed at the same orbital distance, then the planet would take A.  more than twice as long to orbit the Sun. B.  exactly twice as long to orbit the Sun. C.  the same amount of Gme to orbit the Sun. D.  exactly half as long to orbit the Sun. E.  less than half as long to orbit the Sun. Newton used physics to explain
Kepler’s Laws.
Newton s laws of motion explain how objects
interact with the world and with each other.
Newton s first law:
An object at rest will remain at rest, and an object
moving in a straight line at constant speed will
not change its motion, unless an external force
acts on it.
Newton s Laws
Newton s second law:
When a force is exerted on an object, its
acceleration is inversely proportional to its mass:
a = F/m
Newton s third law:
When object A exerts a force on object B, object
B exerts an equal and opposite force on object A.
Gravity
On Earth’s surface,
the acceleration
due to gravity is
approximately
constant, and
directed toward the
center of Earth.
9.8m/s2
Weight = mass x gravity
Mars has 0.38 the gravity Earth has.
What would you weigh on Mars?
Calculate this.
Which of the following best describes how you would weigh on the Moon versus Earth? A.  You would weigh the same B.  You would weigh more on the moon C.  You would weigh less on the moon D.  You would have more mass on the moon, but your weight would not change Moon gravity Demo
Force of gravity depends on mass
and distance.
Distance follows the inverse
square law
If the distance between
two masses quadruples,
how much does the
gravitational force
between them lessen?
Mass (force)= 1/d2
Newton s Laws
Gravity
The gravitational pull
of the Sun keeps the
planets moving in
their orbits.
If the sun were twice as massive its pull on Mars would be A.  Unchanged B.  Twice as much C.  Half as much D.  Four Gmes as much Choose your answer below (Class Ac)on: Gravity, f and d, direc)on, Spaceship to Moon, satellite orbits) A.  A B.  B C.  C D.  D http://astro.unl.edu/classaction/
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Newton s Laws
Massive objects actually orbit around their
common center of mass; if one object is
much more massive
than the other, the
center of mass is not
far from the center of
the more massive
object. For objects
more equal in mass,
the center of mass is
between the two.
The force of gravity between two planets depends on: A.  1) Masses and distance apart B.  2) Planetary atmospheres C.  3) RotaGonal moGons D.  4) All of these Newton s Laws
Kepler s laws are a
consequence of
Newton s laws.
Write 1 sentence to
explain this figure: