Prologue

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ASTRONOMY
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What is Astronomy?

• The study of objects outside the Earth.
  Examples
• The Moon
• What phase is the Moon in tonight? Waxing or
  waning?
• Planets, comets, asteroids
• Are any planets visible? Comets?
• The Sun and stars
• How do stars form and why do they shine?
• Do other stars have planets orbiting them?
• Could there be life on those planets?
• Lots of other stuff galaxies, supernovae, black
  holes,

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Numbers

• Scientific Notation (power of ten)
• 1,000,000 10x10x10x10x10x10 106
• 150,000,000,000,000 150x1012 1.5x1014
• 1 nanosecond 0.000,000,001 seconds 10-9
  seconds

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The Milky Way

• Sun is 30000 LY from the center of our Galaxy.
• From our location within the galaxy, we cannot
  see through its far rim because the space between
  stars is not empty interstellar dust or gas
  which absorbs visible light.
• The interstellar gas is the fuel for the
  formation of stars.
• Yet, interstellar material is very sparse, space
  between stars is quite empty much more so than
  an vacuum one can achieve in the laboratory on
  Earth.
• Possibility of dark matter.
• Star Clusters contain up to hundreds of
  thousands of stars light years across.
• Star have a long life (billions of years) but not
  infinite they die or collapse in spectacular
  ways.

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Nearby objects (Orion Nebula in the Magellanic
Cloud)

• Our galaxy is not unique .
• Many other discovered studied.
• Some are close to us
• Magellanic clouds
• Most are at enormous distances.
• Nearest large galaxy is Andromeda, or M31.

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Local group of galaxies

• M31 is part of a small cluster of over 40
  galaxies one calls the local group.
• At distances of about 10 to 15 million LY, one
  finds other small galaxy groups or clusters.
• At about 50 million LY, one finds a very large
  cluster containing thousands of galaxies called
  the Virgo cluster.
• Some of the observed clusters appear to form
  super clusters.
• Our local group and the Virgo cluster are part of
  one such supercluster which stretches over a
  diameter of 60 million LY.

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• Farthest galaxy (red object) about 1.3 x 1010 LY
• Galaxies are collections of about 1011 stars
• Andromeda galaxy distance 2 x 106 LY
• nearest star 4.3 LY 9.6 x 1012 km
  64,000 AU
• Sun 1 AU 1.5 x 108 km

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Well cover other topics as background

• History of astronomy
• Newtons laws of motion and gravity
• Orbits and motion of objects
• Geology of the Earth
• Comparative geology of other planets
• Atoms and light
• Spectra measured by telescopes
• Nuclear fusion
• The Sun and stars
• Special and general relativity
• Fusion, black holes, and cosmology

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What is Science?

• A science is a methodological study following the
  scientific method.
• The scientific method has 5 steps
• Observation
• Observe some phenomenon to be studied
• Hypothesis
• Develop a hypothesis of the phenomenon
• Prediction
• Derive a testable prediction from the hypothesis
• Measurement
• Make a measurement that tests the prediction
• Conclusion
• Verify or refute the prediction, adjust the
  hypothesis as necessary

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Laws of Nature

• Some scientific hypotheses are so well verified
  in a wide variety of situations that they become
  elevated to the status of laws of nature.
• Newtons laws of motion and gravitation
• Conservation of momentum and energy
• Ideal gas law
• Conservation of mass/atoms
• Cell theory
• DNA
• Evolution

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Numbers
Word Number Sci. Not. Prefix
trillion 1,000,000,000,000 1012 Tera (T)
billion 1,000,000,000 109 Giga (G)
million 1,000,000 106 Mega (M)
thousand 1,000 103 kilo (k)
1 100
thousandth 0.001 10-3 milli (m)
millionth 0.000001 10-6 micro (µ)
billionth 0.000000001 10-9 nano (n)
trillionth 0.000000000001 10-12 pico (p)
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Speed of Light

• How fast does light travel?
• About 300,000 km/s 11,000,000 km/hr
• The distance that light travels in one year is
  called a light-year, abbreviated ly 9.5?1012
  km/year.
• While this is a large distance, it is useful for
  quoting distances to other stars.
• Can be generalized to include light-second,
  light-day, etc.
• The Moon is about 1.3 light-seconds from Earth.
• The Earth is about 8 light-minutes from the Sun.

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Astronomy is a Time Machine

• When we observe a star that is 100 light-years
  distant, then the light took 100 years to reach
  us. We are seeing it as it was 100 years ago.
• The nearest galaxy is about a million light-years
  from Earth. We see it as it was 1 million years
  ago.
• The most distant objects observed are about 10
  billion ly from Earth. The light we see left the
  object 10 billion years ago!

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Discussion Question

• What are some of the things you wish to learn
  about in this course?