1. History of Astronomy
Unit 1B

2. Outline I. The Roots of Astronomy A. Archaeoastronomy
B. The Astronomy of Greece
C. The Ptolemaic Universe
II. The Copernican Revolution
A. Copernicus B. Galileo Galilei
III. The Puzzle of Planetary Motion
A. Johannes Kepler
IV. Galileo and Newton
A. Galileo and Motion
B. Newton and the Laws of Motion
C. Mutual Gravitation
V. Orbital Motion
A. Orbital Motion
B. Newton's Version of Kepler's Third Law
VI. Einstein and Relativity
A. Special Relativity
B. The General Theory of Relativity
C. Confirmation of the Curvature of Space-Time

3. _____________________ is the study of the astronomy of ancient peoples.

4. Archaeoastronomy _________ Temples
Many cultures around the world observed the _______ and marked important ___________.
_________ Temples

5. From Archaeoastronomy to the Astronomy of Greece
In most cases, ancient cultures, having no _________ language, left no detailed records of their astronomical beliefs.
______ astronomy, derived in part from Babylon and Egypt, is better known because written documents have __________.

6. The Astronomy of Greece
Greek models were generally ______ because they were based on these “first principles”, believed to be obvious and not questioned:
The Universe is _____________: Earth is the unmoving center of the Universe.
The heavens are perfect and the perfect shape is the ____________, so the heavens must be made of spheres*. * Plato, Pythagoras, and Aristotle all believed this and it went unquestioned for nearly 2000 years.

7. The Astronomy of Greece
Eudoxus (409 – 356 B.C.): Model of __ nested spheres
Aristotle (384 – 322 B.C.), Philosopher, not scientist!
major authority of astronomy until the late middle ages: Universe can be divided in _ parts:
1. ________________, changeable Earth,
2. Perfect ___________ (described by spheres)
He expanded Eudoxus’ Model to use __ spheres.

8. Eratosthenes (~ 200 B.C.): Calculation of the Earth’s radius
Angular distance between Syene and Alexandria: ~ 7°
Linear distance between Syene and Alexandria: ~ 5,000 stadia
 Earth’s Radius ~ 40,000 stadia (probably ~ ___% too large); better than any previous radius estimate.

9. The Ptolemaic Universe
Claudius Ptolemaeus (“___________”) converted Aristotle’s universe into a sophisticated ____________ model in the Amalgest (c. 140 AD)
Retrograde (___________) motion of the planets was hard to explain, so Ptolemy developed ___________ (small circles on the circumference of larger circles) to better _________ the motions of the planets
He kept uniform circular motion and __________

10. Epicycles

12. The Copernican Revolution
Nicolaus Copernicus (1473 – 1543):
_______________ Universe (Sun in the Center)

13. Copernicus the Revolutionary
Copernicus devised a heliocentric (____-centered) model. He preserved the principle of uniform circular motion, but he argued that Earth rotates on its _____ and _______ around the sun once a year.
His theory was ______________ because it contradicted Church teaching.
Copernicus published his theory in his book De Revolutionibus Orbium Coelestium in _______, the same year he died.

14. Copernicus’ new explanation for retrograde motion of the planets
Copernicus the Revolutionary
Copernicus’ new explanation for retrograde motion of the planets
Because Copernicus kept uniform circular motion as part of his theory, his model
did not predict the motions of the planets well, but
did offer a simple explanation of retrograde motion without using big epicycles.

15. Copernicus’ new explanation for retrograde motion of the planets
Copernicus the Revolutionary
Copernicus’ new explanation for retrograde motion of the planets
___________ (backward) motion of a planet occurs when the Earth passes the planet.
This made Ptolemy’s epicycles ___________.

16. Galileo Galilei (1594 – 1642)
Invented the _________ view of science: Transition from a faith-based “science” to an observation-based science.
Greatly improved on the newly invented _______ technology. (But Galileo did NOT invent the telescope!)
Was the first to meticulously report telescope observations of the sky to support the ___________________ Model of the Universe.

17. Johannes Kepler (1571 – 1630) Circular motion and Uniform motion.
Used the precise observational tables of ___________ (1546 – 1601) to study planetary motion mathematically.
Developed Kepler’s __ Laws of ____________ Motion
Found a consistent description by ______________ both
Circular motion and
Uniform motion.

18. X Johannes Kepler (1571 – 1630) Circular motion and Uniform motion.
Used the precise observational tables of Tycho Brahe (1546 – 1601) to study planetary motion mathematically.
Developed Kepler’s 3 Laws of Planetary Motion
Found a consistent description by abandoning both X
Circular motion and
Uniform motion.

19. Kepler’s First Law of Planetary Motion
The orbits of the planets are ___________ with the sun at one focus. c
Eccentricity e = c/a

20. Kepler’s Second Law of Planetary Motion
A line from a planet to the sun sweeps over _______ areas in equal intervals of ______.
*Planets move _________ when they are close to the Sun

21. Kepler’s Third Law of Planetary Motion
_________ where P is the ______ of orbit in Earth years and A is the semi-major ___ of the orbit in AU

22. _____________ as a tool for understanding physics
A New Era of Science
_____________ as a tool for understanding physics

23. Isaac Newton (1643 - 1727) Major achievements:
Built on the results of Galileo and Kepler
Added ______________ interpretations to the mathematical descriptions of astronomy by Copernicus, Galileo and Kepler
Major achievements:
Invented _________ as a necessary tool to solve mathematical problems related to motion
Discovered the three laws of ________
Discovered the universal law of mutual _________

24. Velocity and Acceleration
Acceleration (__) is the change of a body’s velocity (__) with time (__):
Acceleration in the conventional sense (i.e. _________ speed)
a = Dv/Dt
Different cases of acceleration:
Velocity and acceleration are directed quantities (________)!
Change of the _________ of motion (e.g., in circular motion)
__________ (i.e. decreasing speed)

25. Acceleration of Gravity
Acceleration of gravity does not depend on the ________ (or weight) of the falling object!
Iron ball
Wood ball
9.8 m/s2

26. Newton’s Laws of Motion (1)
A body _________ at ______ or in uniform ____________ in a straight line unless acted upon by some net force.
An astronaut floating in space will continue to float forever in a straight line unless some ________________________ is accelerating him/her.

27. Newton’s Laws of Motion (2)
The acceleration a of a body is __________ proportional to its mass m, _________ proportional to the net force F, and in the _______ direction as the net force.
________ _______

28. Newton’s Laws of Motion (3)
For every action, there is an ______ and ___________ reaction.
M = 70 kg
V = ?
The same force that is accelerating the boy forward, is accelerating the skateboard backward.
m = 1 kg
v = 7 m/s

29. The Universal Law of Gravitation
Any two bodies are ______________ each other through gravitation, with a force __________ to the product of their masses and inversely proportional to the square of their _________:
m1m2
F = -G r2
G=6.673 x m3/kg/s2
(G is the Universal _________ of gravity.)

30. The Universal Law of Gravitation
m1m2
F = -G r2
G=6.673 x m3/kg/s2

31. Orbital Motion
In order to stay on a _______ orbit, an object has to be within a certain range of __________:
Too ____ => Object ____ back down to Earth
Too ____ => Object _________ Earth’s gravity

32. Einstein and Relativity
Einstein (1879 – 1955) noticed that Newton’s laws of motion are only correct for ______ velocities, much less than the speed of light.
 Theory of ______ Relativity
Also, revised understanding of gravity
 Theory of General ________

33. Two Postulates Leading to Special Relativity
Observers can never _____ their uniform motion, except relative to other objects.
This is equivalent to:
The laws of physics are the same for all observers, no matter what their motion, as long as they are not accelerated.

34. Two Postulates Leading to Special Relativity
The velocity of light, _, is constant and will be the ____ for all observers, _____________ of their motion relative to the light source.

35. Other Effects of Special Relativity
____ increases: due to the mass-energy equivalence, __ added is converted to _____ instead of v
Distances _______: Length scales on a rapidly moving object appear ________.
Time moves ________: an effect called time dilation
The energy of a body at rest is ____ 0. Instead, we find

36. A new description of _______
General Relativity
A new description of _______
Postulate:
__________________:
“Observers can not distinguish locally between inertial forces due to acceleration and uniform gravitational forces due to the presence of massive bodies.”

37. New description of gravity as curvature of space-time!
General Relativity
Postulate:
______
_________ tells space-time how to curve, and curvature of space time tells mass how to ______________
New description of gravity as curvature of space-time!

38. Thought Experiment (Conclusion)
This _______ of light by the gravitation of massive bodies has indeed been observed:
During total solar eclipses:
The positions of stars apparently ______ to the sun are shifted ______ from the position of the sun.

39. Another manifestation of bending of light: Gravitational lenses
A massive galaxy cluster is bending and focusing the light from a background object.

40. archaeoastronomy
The study of the astronomy of ancient cultures.
eccentricity (e)
A measure of the flattening of an ellipse. An ellipse of e = 0 is circular. The closer to 1 e becomes, the more flattened the ellipse.
ellipse
A closed curve enclosing two points (foci) such that the total distance from one focus to any point on the curve back to the other focus equals a constant.
epicycle
The small circle followed by a planet in the Ptolemaic theory. The center of the epicycle follows a larger circle (deferent) around Earth.
geocentric universe
A model universe with Earth at the center, such as the Ptolemaic universe.
heliocentric universe
A model of the universe with the sun at the center, such as the Copernican universe.
hypothesis
A conjecture, subject to further tests, that accounts for a set of facts.
natural law
A conjecture about how nature works in which scientists have overwhelming confidence.
parallax (p)
The apparent change in position of an object due to a change in the location of the observer. Astronomical parallax is measured in seconds of arc.
retrograde motion
The apparent backward (westward) motion of planets as seen against the background of stars.
semimajor axis (A)
Half of the longest axis of an ellipse.
theory
A system of assumptions and principles applicable to a wide range of phenomena that have been repeatedly verified.
uniform circular motion
The classical belief that the perfect heavens could move only by the combination of constant motion along circular orbits.

41. acceleration
A change in a velocity; a change in either speed or direction. (See velocity.)
acceleration of gravity
A measure of the strength of gravity at a planet's surface.
center of mass
The balance point of a body or system of bodies.
energy
The capacity of a natural system to perform work - for example, thermal energy.
escape velocity
The initial velocity an object needs to escape from the surface of a celestial body.
general theory of relativity
Einstein's more sophisticated theory of space and time, which describes gravity as a curvature of space-time.
kinetic energy
Energy of motion; depends on mass and velocity of a moving body.
mass
A measure of the amount of matter making up an object.
momentum
The tendency of a moving object to continue moving; mathematically, the product of mass and velocity.
potential energy
The energy a body has by virtue of its position. A weight on a high shelf has more potential energy than a weight on a low shelf.
special relativity
The first of Einstein's theories of relativity, which dealt with uniform motion.
velocity
A rate of travel that specifies both speed and direction.