ASTRO 101

1
ASTRO 101

• Principles of Astronomy

2
Instructor Jerome A. Orosz
(rhymes with boris)Contact

• Telephone [phone]
• E-mail orosz_at_sciences.sdsu.edu
• WWW http//mintaka.sdsu.edu/faculty/orosz/web/
• Office Physics 241, hours T TH 330-500

3
Text Perspectives on Astronomy First
Editionby Michael A. Seeds Dana Milbank.
4
Course WWW Page

• http//mintaka.sdsu.edu/faculty/orosz/web/ast101_f
  all2009b.html
• Note the underline ast101_fall2009b.html
• Also check out Nick Strobels Astronomy Notes
• http//www.astronomynotes.com/

5
Astronomy Help Room Hours

• Monday 1200-1300, 1700-1800
• Tuesday 1700-1800
• Wednesday 1200-1400, 1700-1800
• Thursday 1400-1800, 1700-1800
• Friday 900-1000, 1200-1400
• Help room is located in PA 215

6
Homework

• Assigned question due September 10 Question 13,
  Chapter 2 (Why are the seasons reversed in the
  southern hemisphere relative to the northern
  hemisphere?)

7
Speaking of infinity

• Which set is larger
• The set of positive integers (1,2,3,)
• The set of even integers (2,4,6,)

8
Speaking of infinity

• Which set is larger
• The set of positive integers (1,2,3,)
• The set of even integers (2,4,6,)
• Both are the same size since there is a
  one-to-one mapping between the two
• (1, 2, 3, 4, )
• (2, 4, 6, 8, )

9
From Before

• Scientific notation is a way to express very
  large or very small numbers.
• Whenever possible, rescale large numbers or
  compare with more familiar units.

10
Coming Up

• Outline of Scientific Method
• Introduction to the Sky
• Constellations
• Stellar Brightness
• The clockwork of the sky
• Day/night
• Phases of the moon
• The seasons
• Solar and Lunar Eclipses

11
Questions for the Day

• What is the shape of the Earth, and is it
  stationary?
• http//www.alaska.net/clund/e_djublonskopf/Flatea
  rthsociety.htm
• http//fixedearth.com

12
Questions for the Day

• What is the shape of the Earth, and is it
  stationary?
• We all know the answers to the above, but can you
  give evidence for the correct conclusion without
  using modern technology?

13
Next

• The Scientific Method

14
Outline of the Scientific Method
15
Outline of the Scientific Method

• Gather data, make observations, etc.
• Form a hypothesis on how the object of interest
  works.
• Determine the observable consequences of your
  idea, using reasonable assumptions and
  well-established laws.
• Formulate experiments to see if the predicted
  consequences happen.

16
Outline of Scientific Method

• If the new observations agree with the
  predictions great, keep going.
• If the new observations dont agree with the
  predictions start over!

17
Messy Details

• Observations are never exact they have
  measurement uncertainties
• x 3.0 /- 0.5 kg usually means there is a 68
  chance that the true answer is between 2.5 and
  3.5 kg.
• Sometimes there are mistakes or fraud.
• Try to get more data or better data.

18
Messy Details

• Sometimes two different hypotheses make basically
  the same predictions about the outcome of a given
  experiment.
• Think up experiments where the two predicted
  outcomes are different.

19
A Good Recap From Nick Strobel

• http//www.astronomynotes.com/scimethd/s1.htm

20
Carl Sagans Guide to Skeptical Thinking
21
Carl Sagans Guide to Skeptical Thinking

• Whenever possible, there must be independent
  confirmation of the facts.

22
Carl Sagans Guide to Skeptical Thinking

• Whenever possible, there must be independent
  confirmation of the facts.
• Experiments must be repeatable.

23
Carl Sagans Guide to Skeptical Thinking

• Whenever possible, there must be independent
  confirmation of the facts.
• Experiments must be repeatable.
• Encourage debate, get other opinions.

24
Carl Sagans Guide to Skeptical Thinking

• Whenever possible, there must be independent
  confirmation of the facts.
• Experiments must be repeatable.
• Encourage debate, get other opinions.
• Think up more than one hypothesis, think of tests
  to disprove them.

25
Carl Sagans Guide to Skeptical Thinking

• Dont get too attached to an idea because it is
  yours.
• Be willing to start over if your ideas do not
  hold up.

26
Carl Sagans Guide to Skeptical Thinking

• Dont get too attached to an idea because it is
  yours.
• Be willing to start over if your ideas do not
  hold up.
• Quantify predictions to the extent possible
  (dont be vauge).

27
Carl Sagans Guide to Skeptical Thinking

• Dont get too attached to an idea because it is
  yours.
• Be willing to start over if your ideas do not
  hold up.
• Quantify predictions to the extent possible
  (dont be vauge).
• If there is a chain of arguments, every link must
  work.

28
Carl Sagans Guide to Skeptical Thinking

• Ask if the hypothesis can be proven wrong.
• Ideas that are untestable or unfalsifiable are
  not worth too much.

29
Carl Sagans Guide to Skeptical Thinking

• Ask if the hypothesis can be proven wrong.
• Ideas that are untestable or unfalsifiable are
  not worth too much.
• Control experiments are essential. For example,
  if it is claimed that a new pill cures an illness
  20 of the time, we should check to see if the
  spontaneous remission rate is not 20.

30
Carl Sagans Guide to Skeptical Thinking

• Separate the variables. For example, taking an
  aspirin and a nap cures my headaches after two
  hours.
• Did the aspirin alone cure the headache?
• Was it the nap?
• None of the above?

31
Carl Sagans Guide to Skeptical Thinking

• Double Blind studies are also essential since
  study subjects and researchers may influence the
  outcome (either knowing or unknowingly).
• The patient and the doctor do not know who got
  the experimental drug and who got the placebo.

32
What NOT to do
33
What NOT to do

• Ad hominem attack the arguer and not the
  argument.

34
What NOT to do

• Ad hominem attack the arguer and not the
  argument.
• Argument by authority.

35
What NOT to do

• Ad hominem attack the arguer and not the
  argument.
• Argument by authority.
• Argument from adverse consequences.

36
What NOT to do

• Ad hominem attack the arguer and not the
  argument.
• Argument by authority.
• Argument from adverse consequences.
• Absence of evidence is not evidence of absence.

37
What NOT to do

• Begging the question or assuming the answer.
• We must have the death penalty to discourage
  violent crime.

38
What NOT to do

• Begging the question or assuming the answer.
• We must have the death penalty to discourage
  violent crime.
• Observational selection, or counting the hits and
  ignoring the misses.

39
What NOT to do

• Begging the question or assuming the answer.
• We must have the death penalty to discourage
  violent crime.
• Observational selection, or counting the hits and
  ignoring the misses.
• Misunderstanding or misusing statistics.

40
What NOT to do

• Excluded middle or false dichotomy.
• If youre not part of the solution, you are part
  of the problem.

41
What NOT to do

• Excluded middle or false dichotomy.
• If youre not part of the solution, you are part
  of the problem.

42
What NOT to do

• Excluded middle or false dichotomy.
• If youre not part of the solution, you are part
  of the problem.
• Straw man
• You care more about the spotted owl than about
  people.

43
Next

• The Sky

44
The Clockwork of the Universe

• There are many familiar astronomical cycles
• The Day/Night cycle.
• The phases of the Moon (the lunar cycle).
• The seasons of the year.
• The seven day week???

45
Pop Quiz

• What is the shape of the Earth?

46
The Earth

• How do we know the Earth is spherical?

47
The Earth

• How do we know the Earth is spherical?
• Curved shadow of the Earth on Moon during eclipse
• The manner in which ships at sea disappear when
  they sail away
• The fact that as you go north-south certain stars
  disappear

48
Constellations

• People have long made up stories about groups of
  stars that appear close together on the sky.
• Such groupings are called constellations. The sky
  was officially divided up into 88
  constellations in 1930 so that a star is
  associated with only one constellation.

49
Constellations

• The modern constellations have strictly defined
  boundaries by international agreement.

50
Constellations

• Many constellation names are derived from
  characters in Greek or Roman mythology.
• Here is Cassiopeia, with its distinctive W.
• The stars are usually not physically associated
  with each other.

51
Constellations

• Here is the Big Dipper, which is not an
  official constellation but part of a larger
  one.
• Again, the stars are usually not physically
  associated with each other.

52
Constellations

• Taurus the Bull (left) and Orion the hunter
  (right) appear in the winter sky.

53
Stellar Brightness Magnitudes

• Historically (e.g. Hipparcos in the First
  Century), the brightness of stars as seen by the
  eye have been measured on a magnitude scale
• The brightest stars were first magnitude.
• The faintest stars were sixth magnitude.
• Brighter objects have smaller magnitudes.

54
Stellar Brightness Magnitudes

• In modern times, it was discovered that the human
  eye has a nonlinear response to light if one
  source of light has twice the light as a second
  source, then the first source would not appear by
  eye to be twice as bright.
• The response of the eye is logarithmic, so that
  differences of magnitudes correspond to ratios of
  brightness.

55
The Magnitude Scale

• The modern of the magnitude scale is set up so
  that a difference of 5 magnitudes corresponds to
  a ratio of brightnesses of 100.
• Bright objects can have negative apparent
  magnitudes.

56
The Celestial Sphere

• Imagine the sky as a hollow sphere with the stars
  attached to it. This sphere rotates once every
  24 hours. This imaginary sphere is called the
  celestial sphere.
• Even though we know it is not the case, it is
  useful to imagine the Earth as being stationary
  while the celestial sphere rotates around it.

57
The Celestial Sphere

• The north celestial pole is directly above the
  north pole on the Earth.
• The south celestial pole is directly above the
  south pole on the Earth.
• The celestial equator is an extension of the
  Earths equator on the sky.
• The zenith is the point directly over your head.
  The horizon is the circle 90 degrees from the
  zenith.

58
The Celestial Sphere

• The celestial poles and the celestial equator are
  the same for everyone.
• The zenith and the horizon depend on where you
  stand.
• http//www.astronomynotes.com/nakedeye/s4.htm

59
Stellar Coordinates and Precession

• There are a few ways to specify the location of a
  star (or planet) on the sky
• Altitude/Azimuth
• The altitude describes how many degrees the star
  is above the horizon, the azimuth describes how
  far the star is in the east-west direction from
  north.
• The altitude and azimuth of a star is constantly
  changing owing to the motion of the star on the
  sky!

60
Stellar Coordinates and Precession

• There are a few ways to specify the location of a
  star (or planet) on the sky
• Equatorial system
• Lines of longitude on the earth become right
  ascension, measured in units of time. The RA
  increases in the easterly direction.
• Lines on latitude on the earth become
  declination, measured in units of degrees.
  DEC90o at the north celestial pole, 0o at the
  equator, and -90o at the south celestial pole.
• http//www.astronomynotes.com/nakedeye/s6.htm

61
Stellar Coordinates and Precession

• The north celestial pole moves with respect to
  the stars very slowly with time, taking 26,000
  years to complete one full circle.

62
The Clockwork of the Universe