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V. Earth and Space. Models for the Universe The Solar System. A. Models for the Universe. Earliest Ideas Mathematical Models and Shifting Paradigms 20 th Century The Current View. A. 1. Earliest Ideas. Early observations of the sky Early explanations of the sky

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v earth and space
V. Earth and Space
  • Models for the Universe
  • The Solar System
a models for the universe
A. Models for the Universe
  • Earliest Ideas
  • Mathematical Models and Shifting Paradigms
  • 20th Century
  • The Current View
a 1 earliest ideas
A. 1. Earliest Ideas
  • Early observations of the sky
  • Early explanations of the sky
  • Significance of the sky:Astrology
  • Features of the sky:
    • Sun & moon
    • Stars
    • Planets: “Wanderers” with seemingly irregular “retrograde” motion that puzzled the ancients
    • http://csep10.phys.utk.edu/astr161/lect/retrograde/retrograde.html
a 2 mathematical models
A. 2. Mathematical Models
  • Ptolemy (~100)
    • Wrote The Almagest
    • Geocentric model of the universe
    • “Epicycles” provided an empirical solution to the problem of retrograde motion
    • His model accurately predicted the motion of the planets, and was the basis of medieval astronomy/astrology (with periodic corrections) for some 1400 yrs
    • http://csep10.phys.utk.edu/astr161/lect/retrograde/aristotle.html http://seds.lpl.arizona.edu/nineplanets/psc/theman.html
a 2 mathematical models5
A. 2. Mathematical Models
  • Copernicus (~1500)
    • Proposed a heliocentric model for the universe
    • Did not eliminate circular orbits
    • Required fewer epicycles than Ptolemy's model; however, predictions from Copernicus’ model were not as accurate as from Ptolemy's
    • http://csep10.phys.utk.edu/astr161/lect/retrograde/copernican.html
a 2 mathematical models6
A. 2. Mathematical Models
  • Galileo (~1600)
    • Observations with his telescope provided empirical support for the Copernican model of the solar system
    • http://csep10.phys.utk.edu/astr161/lect/history/galileo.html
a 2 mathematical models7
A. 2. Mathematical Models
  • Kepler (~1600)
    • An assistant of Tycho Brahe
    • Developed a heliocentric model of the solar system based on elliptical planetary orbits
    • “Kepler’s Laws of Planetary Motion”
    • http://csep10.phys.utk.edu/astr161/lect/history/kepler.html
a 2 mathematical models8
A. 2. Mathematical Models
  • Newton (late 1600s)
    • Developed mathematical “laws of motion” to explain velocity & acceleration
    • Developed calculus
    • Developed a “theory of gravitation” based on the concept of “force at a distance”
      • Every object in the universe attracts every other object with a force directed along a line that connects the centers of the two objects. The force is proportional to the masses of the two objects and is inversely proportional to the squares of the distances between the two objects.
    • Demonstrated that Kepler’s laws could be derived from the laws of motion & gravitation
    • http://csep10.phys.utk.edu/astr161/lect/history/newton.html
a 2 mathematical models9
A. 2. Mathematical Models
  • Maxwell (~1850)
    • Developed a field theory of electromagnetism
    • Explained the “lines of force” observed in a magnetic field (for example, if you sprinkle powdered iron around a magnet)
    • http://www.phy.hr/~dpaar/fizicari/xmaxwell.html
    • http://micro.magnet.fsu.edu/electromag/java/magneticlines/
a 3 20 th century
A. 3. 20th Century
  • Einstein (Early 1900s)
    • Einstein’s ideas indicated that Newton’s “laws” of motion & gravity were, in fact, only approximations that did not account for the behavior of matter, space, and time at large velocities or in large gravitational fields
  • Einstein links:
    • http://csep10.phys.utk.edu/astr161/lect/history/einstein.html
    • http://encarta.msn.com/encnet/refpages/RefArticle.aspx?refid=761562147&pn=1
    • http://www.pbs.org/wgbh/nova/einstein/
a 3 20 th century11
A. 3. 20th Century
  • Einstein (cont.)
    • Special Theory of Relativity
      • The speed of light in a vacuum is constant, regardless of the perspective of the viewer
      • As an object approaches the speed of light, its size and time approach zero, and its mass approaches infinity
      • Mass and energy are equivalent (E = mc2)
  • Einstein links:
    • http://csep10.phys.utk.edu/astr161/lect/history/einstein.html
    • http://encarta.msn.com/encnet/refpages/RefArticle.aspx?refid=761562147&pn=1
    • http://www.pbs.org/wgbh/nova/einstein/
a 3 20 th century12
A. 3. 20th Century
  • Einstein (cont.)
    • General Theory of Relativity
      • Gravitation and acceleration are equivalent
      • Mass causes the curvature of space-time, accounting for the existence of gravity
      • Several phenomena such as the “bending” of light rays by strong gravitational fields and certain anomalies with the orbit of Mercury could not be explained by Newton’s laws, but were explained by the Einstein's General Theory
  • Einstein links:
    • http://csep10.phys.utk.edu/astr161/lect/history/einstein.html
    • http://encarta.msn.com/encnet/refpages/RefArticle.aspx?refid=761562147&pn=1
    • http://www.pbs.org/wgbh/nova/einstein/
a 3 20 th century13
A. 3. 20th Century
  • Quest for a “unified field theory”
    • Physicists recognize four “fundamental forces:” electromagnetism, strong nuclear force, weak nuclear force, and gravitation
    • A “Unified Field Theory” (sought by Einstein & other physicists) would be a single set of equations that would predict the behavior of these forces in space-time
a 3 20 th century14
A. 3. 20th Century
  • Hubble (1924)
    • Demonstrated that many of the “nebulae” were, in fact, isolated clusters of thousands of stars (galaxies)
    • The Earth’s sun is only one star in the Milky Way galaxy
    • Hubble also demonstrated that other galaxies are “racing away” from the Milky Way: an expanding universe
    • The major evidence for an expanding universe was the “Doppler shift:” The wavelength (color) of light from distant galaxies is “shifted” toward lower wavelengths (toward the red end of the spectrum)
    • http://encarta.msn.com/encnet/refpages/refarticle.aspx?refid=761572208
a 4 the current view
A. 4. The Current View
  • In the mid-20th century, the astronomer George Gamow proposed the “big-bang” hypothesis (name coined by Fred Hoyle in 1950) to account for the expanding universe
  • http://archive.ncsa.uiuc.edu/Cyberia/Expo/cosmos_nav.html
a 4 the current view16
A. 4. The Current View
  • Proposed sequence of the “big bang”
    • The universe begins as a singularity (point)
    • In the first 10-34 sec, the universe “inflates” (expands) and is very “hot,” so energy & matter are indistinguishable (“quark soup”)
    • By 1 sec, the universe has expanded and cooled to the point that stable protons and neutrons can form
    • By 300,000 years, the universe had expanded and cooled (to about 4000°K) enough so that light could pass “through” empty space without bumping into matter
    • The universe continued to expand and cool, to its present temperature of about 4°K. The first galaxies were formed about 1 billion years ago
    • The estimated age of the current universe is between 12 and 15 billion years
    • http://archive.ncsa.uiuc.edu/Cyberia/Expo/cosmos_nav.html
a 4 the current view17
A. 4. The Current View
  • Experimental evidence for the big bang
    • There is a “background” of microwave radiation throughout the universe, predicted by Gamow and others
    • Some features of the earlier universe have been observed by recent telescopes
    • There is slight variability in the background temperature of the universe, a feature that is necessary to explain the existance of galaxies and galactic clusters
  • http://archive.ncsa.uiuc.edu/Cyberia/Expo/cosmos_nav.html
b the solar system
B. The Solar System
  • The nebular hypothesis
  • The sun
  • The inner planets
  • The outer planets
  • Comets

http://seds.lpl.arizona.edu/nineplanets/nineplanets/overview.html

b 1 the nebular hypothesis
B. 1. The Nebular Hypothesis
  • The concept that the solar system formed from a rotating cloud of interstellar gas (mostly hydrogen) and dust
  • Possibly the remnant of a supernova
  • http://csep10.phys.utk.edu/astr161/lect/solarsys/nebular.html
b 2 the sun
B. 2. The Sun
  • Consists of ~75% hydrogen and 25% helium
  • Heat is produced from nuclear fusion (Hydrogen nuclei fuse to form a helium nucleus, with a release of large quantities of energy)
  • http://seds.lpl.arizona.edu/nineplanets/nineplanets/sol.html
b 3 the inner planets
B. 3. The Inner Planets
  • “Rocky” planets with compositions rich in iron and other metals
  • Mercury
  • Venus
  • Earth
  • Mars
  • The asteroid belt
b 4 the outer planets
B. 4. The Outer Planets
  • Jupiter, Saturn, Uranus, and Neptune are classified as “gas giant” planets, rich in hydrogen, with extensive satellite and ring systems
  • Pluto is a small rocky planet beyond Neptune (usually) but with a highly eccentric orbit. It is believed perhaps to once have been a moon of Neptune which escaped its gravitational pull
b 5 comets
B. 5. Comets
  • Balls of ices and dust that orbit the sun in highly eccentric orbits
  • When approaching the sun, part of the comet evaporates and foms the “tail” seen from earth
  • http://seds.lpl.arizona.edu/nineplanets/nineplanets/comets.html