Astro 105: Our Place in the Universe

1
Astro 105 Our Place in the Universe
Lecture 4

• Lecturers
• J.P.Ostriker
• A.E.Shapley
• J.E. Gunn
• P. Steinhardt

2
The Scientific Method(one version)

• (0) Belief the world is real and that it is
  ultimately comprehensible by rational thought and
  experiment.
• (1) Observation quantitative when possible.
• (2) Model construct an intellectual model that
  is internally consistent and fits the data.
• (3) Predict Make falsifiable predictions,
  quantitative if possible.
• (4)Test Compare predictions with observations.
• (5) Iterate Discard false models and improve
  those that work.

3
The Scientific Method(continued)

• (1) Note No experiment or observation can be
  made without uncertainty probable error. How
  can this fact be handled?
• (2) Note In any given subject not all phases are
  followed at all times. Kuhn is right that there
  are critical times when the paradigm is under
  stress.
• (3) Note Not all scientists are working on all
  of these phases. In fact, most work on (1), some
  on (4), and very few on (2), (3) and (5).
• (4) Note Truth is redefined as reachable only
  by successive approximations. Falsity is clearer!

4
Reading

• Berry Greek Astronomy.
• Dreyer The Dimensions of the World.
• Pannekoek The Renascence of Science
• Biographies Copernicus, Tycho, Kepler and
  Galilleo.
• GallileoDialogue Concerning the Two Chief
  Systems of the World.
• Web research Ancient Greek Astronomy

5
Outward Bound History of Cosmic Exploration

• 600BCE-100BCE Pythagoras, Aristarchus,
  Hipparchus
• A Quantitative Model for the Solar System.
• 1550-1650 Tycho Brahe, Johannes Kepler and
  Gallileo Gallilei - The Earth is a Planet
  Revolving, with others, about the Sun.
• 1650 - 1750 Isaac Newton, Edmond Halley, L.
  Euler Physics, Mathematics and Unviversal Laws.
• 1750 - 1920 Thomas Wright, Wilhelm Bessel,
  William and Caroline Herschel, J.C.Kapteyn and
  Harlow Shapley We live in a Galaxy of Stars.

6
Greek Philosophers/Mathematicians

• Carefully observed the world. Sought logical
  explanations for phenomena.
• Made measurements of times, angles and distances,
  which were rough but adequate.
• Knew sufficient geometry and algebra to
  manipulate observed quantities to derive new
  knowledge of the earth/moon/sun system.

7
Greek Philosophers/Mathematicians

• Pythagoras (570-500 BCE ) Mathematician and
  philosopher - earth is an unsupported sphere,
• Aristarchus of Samos (310-230 BCE) Distances to
  the Sun and Moon.
• Eratosthenes of Alexandria (276-195 BCE) Size of
  the Earth
• Hipparchus of Nicea (162-126 BCE) Accurate
  measuremts, refraction, star catalogs
• NB absence of Plato, Aristotle and Romans!

8
Greek Science some questions

• Can you, or anyone, reproduce their arguments?
• Size of the earth
• Earth-moon distance, size of the moon
• Earth-sun distance, size of the sun
• Distance to other planets and to the fixed
  stars
• Age of the Earth?
• Why were their results discarded for centuries in
  the west?
• What caused a revival of interest in astronomy in
  Europe?

9
Aristarchus Erathosthenes
10
Measuring the Size of the Earth
h
s
?
d
?
aearth
s/h d/aearth
11
Renascence in Europe(enabling factors)

• Spirit of inquiry, rediscovery of the classics,
  trade with Byzantium.
• Indian and Arab decimal system replace Roman
  numerals.
• Technology development sextants and then
  telescopes.
• Debate, printing, intellectual intercourse.

12
Renascence in Europe(salient individuals)

• N. Copernicus of Torun (1473-1543) Studied in
  Italy. Solar centered system, used Ptolmeic
  observations with some improvements.
• T. Brahe of Denmark (1546-1601) Great observer.
  Earth and Sun centered system. New star (SN) of
  1572. Died in Prague with J. Kepler his
  mathematical assistant.
• J. Kepler of Germany (1571-1630) Three laws of
  planetary motion.
• G. Galilleo of Pisa/Florence ( 1564-1642) Use of
  telescope, Jupiters satellites, acceleration

13
Renascence in Europe(some questions)

• Religion, Astrology, Observation and Logic Was
  there a conflict among them?
• Progress in Astronomy Was it inevitable?
• What was missing from the new knowledge?
• Hint causation
• Hint spatial scales
• Hint temporal scales
• Would remedying these defects cause problems in
  astronomy? Between science and society?

14
We are put in our place !

• The Earth is but a planet among others, circling
  the sun.
• An apple, a human, the moon and the planets all
  feel the force of gravity.

15
Tycho Brahe measures star and planet positions to
1/100 of a degree.
16
Johannes Kepler puts the planets on ellipses and
puts the Sun in the center.