Starry Monday at Otterbein

1
Starry Monday at Otterbein
Welcome to

• Astronomy Lecture Series
• -every first Monday of the month-
• May 5, 2007
• Dr. Uwe Trittmann

2
Todays Topics

• From Galileo to Newton - The Birth of Modern
  Astronomy, Part II
• The Night Sky in May

3
On the Web

• To learn more about astronomy and physics at
  Otterbein, please visit
• http//www.otterbein.edu/dept/PHYS/weitkamp.asp
  (Observatory)
• http//www.otterbein.edu/dept/PHYS/ (Physics
  Dept.)

4
From Galileo to Newton - the Birth of Modern
Astronomy, Part II
1610 1687
5
Sunspots

• MPEG video from Galileo Project (June 2 July 8,
  1613)

6
Saturn

• Sketch of 1616
• Engraving in The Assayer (1623)

7
Galileo and his Contemporaries

• Elizabeth I. (1533-1603) Queen of England
• Tycho Brahe (1546-1601) Danish Astronomer
• Francis Bacon (1561-1626) English Philosopher
• Shakespeare (1564- 1616) Poet Playwright
• Galileo Galilei (1564-1642) Italian PAM
• Johannes Kepler (1571-1630) German PAM
• Rene Descartes (1596 - 1650) French PPM
• Christiaan Huygens (1629-1695) Dutch PAM
• Isaac Newton (1643-1727) English PM
• Louis XIV (1638-1715) French Sun King

8
Epochs

• Renaissance 1450-1600
• Rebirth, back to the roots
• Baroque 1600-1715
• Epoch of the religious wars
• Later Louis XIV and Newton
• Rococo 1715-1775

9
Tycho Brahe Johannes Kepler Galileo Galilei

• Observations Phenomenology/Theory
  Experiment
• ? Data ? Predictions ? test
  predictions

10
The Scientific Method

• Systematized by Francis Bacon, Descartes and
  Galileo in the 17th century
• Not the only way of knowing, but a very
  successful one
• A method to yield conclusions that are
  independent of the individual
• Conclusions are based on observation

11
Francis Bacon (1561-1626)

• Contemporary of Shakespeare,
• Elizabeth I, Kepler and Galilei
• Rejects Aristotelianism and Scholasticism
• Major Work
• Novum Organum (1620)
• (New Tools, the old Organum was
  Aristotles)

12
Francis Bacon (1561-1626)

• Novum Organum Title
• Allegory on the daring mind A Ship passes
• through the pillars of
• Hercules (the straight of Gibraltar, the end
  of the world), beyond old knowledge.

13
Rene Descartes The Rationalist

• Described the method to do science,
• known for his mind-body dualism
• Major Works
• Discourse (1637) full title Discours de la
  méthode pour bien conduire sa raison et chercher
  la vérité dans les sciences Discourse on the
  Method of Rightly Conducting the Reason, and
  Seeking Truth in the Sciences
• Meditations on first Philosophy (1641)
• 6 Meditations Of the Things that we may
  doubt Of the Nature of the Human Mind Of God
  that He exists Of Truth and Error Of the
  Essence of Material Things Of the Existence of
  Material Things Of the Real Distinction between
  the Mind and the Body of Man

Rene Descartes (1596-1650)
14
Rene Descartes Discourse

• Describes the method to do science
• in a straightforward way (see below)
• Major points
• Science must be based on correct reasoning
  (logic)
• Science must be formulated in mathematical
  language

Starting line Good sense is the most evenly
distributed thing in the world, for all people
suppose themselves so well provided with it that
even those who are the most difficult to satisfy
in every other respect never seem to desire more
than they have.
15
A Classical Example

• Aristotle observes that during lunar eclipses the
  Earths shadow on the moon is curved
• He assumes it will be curved for all eclipses
• A hypothesis that explains this the earth is
  round
• A prediction of this theory is that the location
  of the stars in the sky should be different for
  observers at different latitudes
• This is confirmed by additional observations
• E.g. Canopus is visible in Egypt but not further
  north

16
Scientific Theories

• Must be falsifiable
• There must be some way the theory could fail
• Should make predictions
• The more, the better!
• Theories that are very well tested and have the
  widest applicability are often known as laws of
  nature
• Always subject to revision or modification
• Occams razor the simplest theory wins

17
Common Misconceptions

• Theories can be proven
• Fact they cannot! If an experiment agrees 10
  billion times with predictions, maybe the next
  experiment disagrees
• However one disagreeing experiment can falsify
  the theory
• Most probably, the sun will rise tomorrow but
  no guarantees!

18
Common Misconceptions

• Theories are just theories, i.e. hypotheses
• Fact scientists call a hypothesis a theory if it
  is very well tested, e.g. Einsteins theory of
  Relativity, Darwins theory of evolution
• There may be hundreds of thousands of reviewed
  publications that independently lend evidence to
  the theorys correctness

19
Common Misconceptions

• Scientists will defend their theories against any
  new and/or unconventional approach
• Fact scientists love new ideas that explain
  everything known to date and make new
  predictions
• However, since so much is known, it is very
  unlikely that someone comes up with a better
  description of Nature than the previous,
  well-tested one
• Unless the new theory is simpler, or makes
  correct predictions at odds with the old theory,
  it is quite efficient to stay with the old theory

20
Common Misconceptions

• Scientists want to explain everything
• Fact scientists want to come up with an accurate
  description of Nature, i.e. of how the
  fundamental entities in the universe interact
• Naturally, science cannot (and does not want to)
  say anything about topics like God, Religion,
  Freedom, Ethics, Art, etc.

21
Common Misconceptions

• Scientists can predict everything that will
  happen in the Universe (Laplaces Demon)
• Fact even in principle (if you would know the
  position and position of every particle) this is
  not possible because of
• Quantum Mechanics the laws of QM are inherently
  stochastic QM predicts the probability of what
  might happen, not what will actually happen
• Possibility of chaotic behavior very small
  differences in the initial conditions can have
  vastly different effects (a butterflys wing
  movements can stir up a hurricane, in principle)

22
The New Physics Astronomy in a Nutshell
Newtons Principia

• Newtons key question
• Why are things happening?
• Invented calculus and physics while on vacation
  from college
• His three Laws of Motion, together with the Law
  of Universal Gravitation, explain all of Keplers
  Laws (and more!)
• Principia (1687)
• Full title Philosophiae naturalis principia
  mathematica has his famous three laws on page 19
  of 443.

Isaac Newton (16421727)
23
Newtons Laws of Motion

1. Every body continues in a state of rest or in a
   state of uniform motion in a straight line unless
   it is compelled to change that state by forces
   acting on it (law of inertia)
2. The change of motion is proportional to the
   motive force impressed (i.e. if the mass is
   constant, F ma)
3. For every action, there is an equal and opposite
   reaction (Thats where forces come from!)

24
Newtons Laws
Always the same constant pull

• a) No force particle at rest
• b) Force particle starts moving
• c) Two forces particle changes movement
• Gravity pulls baseball back to earth
• by continuously changing its velocity
• (and thereby its position)
• 
  ?

25
Law of Universal Gravitation

• Force G Mearth Mman / R2

26
Orbital Motion
27
Cannon Thought Experiment

• http//www.phys.virginia.edu/classes/109N/more_stu
  ff/Applets/newt/newtmtn.html

28
Applications

• From the distance r between two bodies and the
  gravitational acceleration a of one of the
  bodies, we can compute the mass M of the other
• F ma G Mm/r2 (m cancels out)
• From the weight of objects (i.e., the force of
  gravity) near the surface of the Earth, and known
  radius of Earth RE 6.4?103 km, we find ME
  6?1024 kg
• Your weight on another planet is F m ? GM/r2
• E.g., on the Moon your weight would be 1/6 of
  what it is on Earth

29
Applications (contd)

• The mass of the Sun can be deduced from the
  orbital velocity of the planets MS
  rOrbitvOrbit2/G 2?1030 kg
• actually, Sun and planets orbit their common
  center of mass
• Orbital mechanics. A body in an elliptical orbit
  cannot escape the mass it's orbiting unless
  something increases its velocity to a certain
  value called the escape velocity
• Escape velocity from Earth's surface is about
  25,000 mph (7 mi/sec)

30
Objections to the Heliocentric Model Answered

• If the Earth is moving, why do dropped objects
  appear to fall straight down?
• Dropped objects start with the velocity of Earth
  (Galileo)
• If the Earth rotates, why don't we get thrown
  off?
• Earth's rotation isn't fast enough!
• If the Earth revolves around the Sun, why don't
  we observe stellar parallax?
• It's there, but very small, because the stars are
  so far away (Aristarchus)
• Why don't we feel the wind of our motion?
• The air moves along with the Earth

31
Problems of Both Models

• Lack of a fundamental explanation?
• Provided by Newton (but what explains Newton?!)
• Lack of direct evidence?
• Proof that the Earth rotates
• Coriolis force (hurricanes are counterclockwise
  in the Northern Hemisphere)
• Foucault pendulum
• Proof that earth and other planets revolve around
  the sun
• Aberration of starlight observed 1729
• Stellar parallax observed 1838
• Phases of Venus (Galileo)

32
The Night Sky in May

• Nights still long, but EDT gt later observing!
• Spring constellations are up Cancer, Leo, Big
  Dipper
• Saturn dominates the evening, Jupiter early
  morning.

33
Moon Phases

• Today Waning Gibbous Moon
• 5 / 10 (Last quarter Moon)
• 5 / 16 (New Moon)
• 5 / 23 (First Quarter Moon)
• 5 / 31 (Full Moon)

34
Today at Noon

• Sun at meridian, i.e. exactly south

35
10 PM

• Typical observing hour, early May
• Jupiter
• Saturn

36
Zenith

• Big Dipper points to the north pole

37
South

• Saturn near Praesepe (M44), an open star cluster

38
South

• Spring constellations
• Leo
• Hydra
• Crater
• Sextans

39
East

• Canes Venatici
• M51
• Coma-Virgo Cluster
• Globular Star Clusters
• M3, M5

40
East

• Virgo and
• Coma
• with the Virgo-Coma galaxy cluster

41
Virgo-Coma Cluster

• Lots of galaxies within a few degrees

42
M87, M88 and M91
43
East

• Hercules
• Corona
• Borealis
• Bootes

• Globular Star
• Clusters
• M 3
• M 13
• M 92

44
M13 Globular Cluster
45
Mark your Calendars!

• Next Starry Monday October 1, 2007, 7 (!!!) pm
• (this is a Monday
  )
• Observing at Prairie Oaks Metro Park
• Friday, May 25, 2007, 900 pm
• Web pages
• http//www.otterbein.edu/dept/PHYS/weitkamp.asp
  (Obs.)
• http//www.otterbein.edu/dept/PHYS/ (Physics
  Dept.)

46
Mark your Calendars II

• Physics Coffee is every Wednesday, 330 pm
• Open to the public, everyone welcome!
• Location across the hall, Science 256
• Free coffee, cookies, etc.