Astronomy 1020: Stars, Galaxies and the Universe

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Astronomy 1020 Stars, Galaxies and the Universe

• Prof. Paul J. Wiita
• Rm 715, One Park Place, wiita_at_chara.gsu.edu
• Phone [phone]
• URL chara.gsu.edu/wiita (syllabus, assignments,
  summary of notes)
• Labs in 516 Kell Hall
• 80318 Mondays, 9-1050 AM
• 80319 Thursdays, 11AM-1250 PM
• 80320 Fridays, 9-1050 AM

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What will we study?

• Astronomy star knowledge
• We examine stars, galaxies cosmos.

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The Scientific Method

• How do we learn anything about the Universe?

We will frequently refer to the concepts of the
Scientific Method, and even when we dont, you
should be thinking about how it applies in each
part of the course (and throughout your
life!). The key element is curiosity! I hope your
previous studies havent completely eliminated
that characteristic from your personality.
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The First Steps in the Scientific Method

• Observe use your senses or augmentations of them
  (microscope or telescope).
  Example the sky is blue.
• Hypothesize (come up with a possible explanation
  of the observation).
• Someone has painted it blue.
  Blue light is more easily scattered
  than red, so the blue sky is scattered sunlight.
• 3. Test HYPOTHESIS through a PREDICTION.
  If the latter is true, then if sunlight passes
  through more of the atmosphere, the sun should
  lose green and yellow light too and appear red.
  (When does this happen?)

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Blue light scatters more in the atmosphere

• Off molecules (strongly) and off dust (less so,
  however).

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Testing Hypotheses

• 4a. perform EXPERIMENT
• 4b. OR make new OBSERVATION
  Sun is indeed red/orange near dawn and dusk
• 5a. If in agreement, perform new test (and keep
  doing so).
• 5b. If in disagreement, discard or modify
  hypothesis
• GO BACK TO STEP 2!
• Only if MANY tests are passed can a HYPOTHESIS be
  called a THEORY.
• If the THEORY applies in a wide range of
  situations, it may be raised to the status of a
  LAW (e.g., Newton's LAW of Gravity)

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In SCIENCE nothing is ever PROVEN

• STILL, even a LAW can be wrong (or partly right)
• Einstein showed that Newton's Laws don't hold
  exactly if
• velocities are close to the speed of light
  (special relativity) OR if
• lots of mass is concentrated in a small volume
  (general relativity).
• SO NOTHING IN A REAL SCIENCE IS EVER ABSOLUTELY
  PROVEN TRUE, although most
  of what is discovered and tested in a "hard"
  science is VERY LIKELY to be correct.

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Types of Hard Sciences

• Categorize
  astronomy, biology,
  chemistry, geology,
  medicine, meteorology,
  oceanography, physics as
• OBSERVATIONAL or EXPERIMENTAL sciences.

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The REAL Scientific Method

• But the preceding is idealized.
• In reality, even good scientists often don't
  discard hypotheses when they fail an
  experimental or observational test.
• Why not?
• A. Experiment is wrong.
• B. Experiment is misinterpreted.
• C. Psychological/sociological/political
  difficulty in giving up long-held
  beliefs.
• Eventually the weight of evidence becomes
  overwhelming and there is a PARADIGM SHIFT or
  SCIENTIFIC REVOLUTION.
  (e.g., Copernican, Darwinian, Quantum Mechanics)

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Characteristics of Sciences

• The above are characteristics of ANY SCIENCE.
• The key point scientific results are
  falsifiable.
• If they cannot eventually be tested, they fall
  outside the realm of science and enter
  philosophy, religion, etc.
• Pseudo-sciences do not allow themselves to be
  tested and true believers refuse to consider
  strong evidence against their validity.
  Examples?
• astrology, alchemy, numerology, palmistry,
  crystal/pyramid power

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Types of Sciences

• What about anthropology, economics, history,
  political science, psychology, sociology?
• These social or "soft" sciences rely to one
  extent or another on scientific methods, but
  also invariably carry a great number of
  preconceptions that allow for many disparate
  interpretations to be drawn from the same data.
• In the natural or "hard" sciences, the range of
  allowed interpretations is usually much less.

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Astronomy vs. Astrophysics

• Aside from the OBSERVATIONAL - EXPERIMENTAL
  dichotomy, since the advent of calculus we have
  distinguished these approaches from THEORETICAL
  science, driven by applied mathematics.
• ASTRONOMY IS AN OBSERVATIONAL SCIENCE.
• ASTROPHYSICS IS AN OBSERVATIONAL -THEORETICAL -
  EXPERIMENTAL SCIENCE.
• Today we typically use these terms
  interchangeably since so much of what we learn
  combines observations with theory and some
  experimental work (laboratory astrophysics).
• We also must consider COMPUTATIONAL science as a
  (nearly) equal partner.

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Review of Scientific Notation

• 102 100, 10110, 100 1, 10-10.1, 10-20.01
• 109 1,000,000,000 billion (Giga-)
• 106 1,000,000 million (Mega-)
• 103 1,000 thousand (kilo-)
• 10-2 0.01one-hundredth (centi-)
• 10-3 0.001one-thousandth (milli-)
• 10-6 0.000001one-millionth (micro-)
• 10-9 0.000000001one-billionth (nano-)
• 5.4x1035,400 7.05x10-30.00705
• 4,7004.7x103 0.017 1.7x10-2

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Powers of Ten Arithmetic

• Multiplication
• (5.3x103) x (6x10-5) 31.8x103(-5)
• 31.8x10-2 3.18x10-1
• 0.318 0.3
• One significant figure! Keep the minimum number
  of significant figures going in.
• Division
• (9.3 x10-4)/(3.10x10-6) 3.0 x10-4-(-6)
• 3.0 x102
• 300
• BUT, 3.0x102 is the better answer, as it CLEARLY
  has two significant figures scientific notation
  is PRECISE.

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The Scales of the Universe
We deal with the largest possible things -- the
whole universe -- and with the smallest -- nuclei
of atoms.
This requires us to use a wide range of PHYSICAL
UNITS and we USE THE METRIC SYSTEM.
Length m or cm Mass kg or g Time s or
yr Temperature K(elvins)
1 pc 3.26 light-yr 3.085678 x
1018cm3.1x1013km
1AU 1.496x1013cm 150,000,000 km (astronomical
unit mean distance between earth and sun)
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Sizes of Everything

• Universe open or flat -- infinite closed --
  1028cm
• Galaxies no of stars 109-1013 size
  1023cm3x104pc
• Stars 1010-1012cm (most radii)
• Typical separations 1018cm 1 pc
• Planets RE6.4x103km 6.4x108cm
• Separations 1 AU
• Mountain Tallest 10 km Hm/RE6.4km/6.4x103km1
  .0x10-3
• People 1.5m 1.5x102cm (5 feet)
• Visible light wavelength500nm5x10-5cm
• Atom 0.1nm10-8cm10-10m (X-ray wavelength)
• Nucleus 1 Fermi 10-13cm 10-15m

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Time Scales of the Universe

• Time since the Big Bang 1.4x1010 yr
• Galaxies formed 1.3x1010 yr ago
• Solar system formed 4.55x109 yr ago
• Oldest rocks on Earth 3.8x109 yr BP
• Earliest life forms 3.5x109 yr BP
• Earliest hominids2x106 yr BP
• Mountains Appalachians2.5x108yr BP
  Rockies 7x107 yr BP
• Human lifespan 75 yr
• Oscillation time for visible light 2x10-15 s
• Time for light to pass the nucleus of an atom
  3x10-24s