Transcript Earth and Space

V. Earth and Space
A. Models for the Universe
B. The Solar System
A. Models for the Universe
1. Earliest Ideas
2. Mathematical Models and Shifting
Paradigms
3. 20th Century
4. The Current View
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
 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 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 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 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 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 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.
th
20
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.
th
20
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.
th
20
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.
th
20
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.
th
20
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
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 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 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
1. The nebular hypothesis
2. The sun
3. The inner planets
4. The outer planets
5. Comets
http://seds.lpl.arizona.edu/nineplanets/nineplanets/overview.html
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
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
“Rocky” planets with compositions rich in
iron and other metals
Mercury
Venus
Earth
Mars
The asteroid belt
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
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