Astronomy 3

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Astronomy 3

• Lecture 1

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• Astrology and Astronomy- the two subjects had
  common origin Court astronomers in China
  discovered the Crab Nebula in 1054 A.D.
• Their duty was to watch sky for emperor and to
  determine favored dates for action. Predict
  eclipses, keep calendar.
• Astrology- a mystical, dead end
• Astronomy - astro nomos names, knowledge
  of stars
• Astrophysicsstudy of the physical properties of
  astronomical systems to describe as well as to
  explain by means of universal physical principles
  the diversity of the Universe
• Cosmology - study of the Universe
• Descriptive Cosmology-- topic of this course,
  minimal math.

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• Astronomy is probably the oldest science and had
  critical role in birth of modern science- the
  source of all technology and of vast knowledge,
  especially self-knowledge.
• EXAMPLES
• . What is the nature and origin of matter, space,
  and time?
• . What is the nature and origin of life and
  intelligence?
• . How do we fit into the grand scheme of the
  Universe?

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The Birth of Science Desire to
Extract Order from Disorder Regularity
from Chaos Science Pseudoscience Religion
Application to
Mystical Ideas Spiritual World and physical
world and Quackary Moral Code
Einsteins theory
Planet X the Earth is 6023 yrs old of
Relativity
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Science as Part of Human Culture At their most
sublime, the ideas from science are every bit as
beautiful as the ideas from music, art, or
literature In an earlier age, people had a much
greater appreciation of the wonders of the
night sky Creation MythsCosmological concepts
are important to all cultures. (Big Bang
CosmologyModern Creation story) Dantes Divine
Comedy Shakespeares Hamlet, the moist star
upon whose influence Neptunes empire stands
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• Role of Astronomy for ancients
• Celestial NavigationPolaris, the pole
  star
• tracking constellations for timekeeping. When is
  the proper time for planting crops?
• Establishment of calendar, 7 days of week for the
  7 wanderers known to the ancients
• Sun Sunday Dimanche
• Moon Monday Lundi
• Mars Tuesday Mardi
• Mercury Wednesday Mercredi
• Jupiter Thursday Jeudi
• Venus Friday Vendredi
• Saturn Saturday Samedi
• Moon orbits Earth in 29.5 days ? 12 months
  354 days, not a full year.
• Lunar based calendar would need frequent
  readjustment
• 3600 in circle, probably from Babylonian
  estimates, 2000 B.C. (motion of Sun across sky
  approx. 10/day (one revolution/year))
• Constellations tell the seasonsOrion
  overhead on Winter eveningsAndromeda
• overhead now. (picture on front slide)

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• The Size of the Universe
• Exponential NotationEssential for astronomical
  scales
• 10n 1000000 10-n .00001
• n zeros (n6) (n-1) zeros (n-5)
• Astronomers generally use cgs units (grams, cm,
  sec)
• (1 inch 2.54 cm)
• (1 pound 454 gm)
• (1 year 3.16 107 sec ? ? 107 sec)
• text uses km105 cm, kg 103 gm
• Unit of Energy joule kg m2 sec-2
• Unit of power joules/sec Watt

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• Rough Scales, Large and Small
• size mass age
• proton 10-15 m 10-27 kg ? 1017 years?
• child 1 m 10 kg 108 sec
• Sun 109 m 1030 kg 1017 sec
• Galaxy 1020 m 1042 kg 1017 sec
• Observable 1026 m 1052 kg 1017 sec
• Universe
• The Universe, although old, is not
  infinitely old
• Light distances c 3 105 km/s
• 1 light second 3 105 km
• 1 light year 9.5 1012 km ? 1013 km
• Range of densities
• water 1 gm/cm3 106 gm/m3 103 kg/m3
• mean density of matter in Universe 10-27 kg/m3
• density of neutron star nuclear density 1017
  kg/m3

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The Orion Nebula
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The formation of solar systems! Each disk 5x
the distance of Sun to Pluto
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• Astronomy without telescopes
• What can one infer from visual observations
  alone?
• rotation of sky
• celestial sphere- fixed crystalline sphere
  wanderers (planets)

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• Celestial navigation
• use compass to determine magnetic North
• at night seek Polaris (if in N. hemisphere and
  not cloudy)

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• Determination of latitude
• angular height of Polaris above horizon
• height of bright star or Sun above horizon when
  it transits meridian (need a book or good
  knowledge of sky)
• Determination of longitude is much harder
• compare local solar time to time on precise
  watch
• measure time of transit of bright star according
  to watch set to Greenwich time. (use book
  listing positions of stars-- Nautical Almanac
• (methods require accurate clocks, and longitude
  measurement before 1700's was extremely
  imprecise!)
• Modern navigation GPS
• Global positioning satellites (24 satellites)
  broadcast very precise clock signals
• by triangulating signal of 3 or more satellites
  simultaneously, a cheap hand-held receiver can
  infer position to precision of a few meters!!

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• Planets all move in nearly the same plane as the
  sun (ecliptic plane)
• (what then are the comets?? portents of
  disaster??)
• Angular size of planets is less than resolution
  of eye appear as points
• Ancient Greeks knew North Pole was higher in sky
  if one went North of Greece.
• Motion of some planets had complex retrograde
  components. How to predict their positions?
• How to predict eclipses of the sun and the moon?

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how to explain the seasons-(summer, winter
solstice Spring, Fall equinox) (alignment of
ancient buildings, e.g. Stonehenge)
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A New Explanation

• In the beginning there was neither space nor time
  as we know them, but a shifting foam of strings
  and loops, as small as anything can be. Within
  the foam, all of space, time and energy mingled
  in a grand unification. But the foam expanded and
  cooled. And then there was gravity, and space and
  time, and a universe was created. There was a
  grand unified force that filled the universe with
  a false vacuum endowed with a negative pressure.
  This caused the universe to expand exceedingly
  rapidly against gravity. But this state was
  unstable, and did not last, and the true vacuum
  reappeared, the inflation stopped, and the grand
  unified force was gone forever. In its place were
  the strong and electroweak interactions, and
  enormous energy from the decay of the false
  vacuum. The universe continued to expand and
  cool, but at a much slower rate. Families of
  particles, matter and antimatter, rose briefly to
  prominence and then died out as the temperature
  fell below that required to sustain them. Then
  the electromagnetic and the weak interaction were
  cleaved, and later the neutrinos were likewise
  separated from the photons. The last of the
  matter and antimatter annihilated, but a small
  remnant of matter remained. The first elements
  were created, reminders of the heat that had made
  them. And all this came to pass in three minutes,
  after the creation of time itself. Thereafter the
  universe, still hot and dense and opaque to
  light, continued to expand and cool. Finally the
  electrons joined to the nuclei, and there were
  atoms, and the universe became transparent. The
  photons which were freed at that time continue to
  travel even today as relics of the time when
  atoms were created, but their energy drops ever
  lower.

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• And a billion years passed after the creation of
  the universe, and then the clouds of gas
  collapsed from their own gravity, and the stars
  shone and there were galaxies to light the
  universe. And some galaxies harbored at their
  centers giant black holes, consuming much gas,
  and blazing with exceeding brightness. And still
  the universe expanded. And stars created heavy
  elements in their cores, and then they exploded,
  and the heavy elements went out into the
  universe. New stars form still and take into
  themselves the heavy elements from the
  generations that went before them. And more
  billions of years passed, and one particular star
  formed, like many others of its kind that had
  already formed, and would form in the future.
  Around this star was a disk of gas and dust. And
  it happened that this star formed alone, with no
  companion close by to disrupt the disk, so the
  dust did condense, and formed planets, and
  numerous smaller objects. And the third planet
  was the right size and the right distance from
  its star so that rain fell upon the planet and
  did not boil away, nor did it freeze. And this
  water made the planet warm, but not too warm, and
  was yet a good solvent, and many compounds
  formed. And some of these compounds could make
  copies of themselves. And these compounds made a
  code that could be copied and passed down to all
  the generations. And then there were cells, and
  they were living.
• And billions of years elapsed with only the
  cells upon the planet. Then some of the cells
  joined together and made animals which lived in
  the seas of the planet. And finally some cells
  from the water began to live upon the rocks of
  the land, and they joined together and made
  plants. And the plants made oxygen, and other
  creatures from the seas began to live upon the
  land. And many millions of years passed, and
  multitudes of creatures lived, of diverse kinds,
  each kind from another kind. And a kind of animal
  arose and spread throughout the planet, and this
  animal walked upon two feet and made tools. And
  it began to speak, and then it told stories of
  itself, and last it told this story. But all
  things must come to their end, and after many
  billions of years, the star will swell up and
  swallow the third planet, and all will be
  destroyed in the fire of the star. And we know
  not how the universe will end, but it may expand
  forever, and finally all the stars will die and
  the universe will end in eternal darkness and
  cold.