PowerPoint Presentation Copernicus

1
Announcements

• Lunar Eclipse Feb 20 (Next Wednesday)!!!!
  Next Tuesdays class will be devoted to the moon
  and the eclipse. Well watch from the mall on
  Wednesday evening. No class next Thursday - but
  there will be homework related to our lunar
  observations.
• Homework 2 is due now. Homework 3 will be posted
  today, due Feb 21 (Thursday).
• Astrobiology Lecture Tonight
• Essay Topics due Today.

2
Date    Tuesday February 12, 2008 Time
   Lecture (7pm) followed by book signing
(8pm) Place   Center for Creative Photography
(UA Main Campus). Gregory Benford, Author and
Astrophysicist at UC Irvine "Seeking
Ozymandias Building and Searching for
Beacons What would transmitters be like if built
by civilizations with a variety of motivations,
but who cared about cost? We have considered the
physical limitations a beacon builder would face
in constructing extremely high power radiators.
Beacons built by distant advanced, wealthy
societies may have very different characteristics
from what SETI researchers now seek.Very high
power systems have driving factors set by
fundamental properties of materials, such as
cooling of such high powers. The Principle of
Parsimony suggests that beacon will compete with
other social goods, for altruistic reasons. Such
Beacons will have narrow beam widths, be pulsed
and broadband, to minimize costs. Therefore, the
transmission strategy for a distant beacon may be
a rapid scan of the galactic plane, to cover the
angular space. Searches for such intermittent,
broadband signals could find signals we have
neglected, because we believed earlier that the
Beacon builders will be spendthrifts. Yet stable
societies do not sacrifice their societies for
distant others. Perhaps we should consider
long-term stability from a moral point of view.
3
Finally we shall place the Sun himself at the
center of the Universe. All this is suggested
by the systematic procession of events and the
harmony of the whole Universe, if only we face
the facts, as they say, with both eyes open
- Nicolaus Copernicus De Revolutionibus
orbium coelestium
There was music in the cafes at night and
revolution in the air. - Bob Dylan
4
Copernicus (1473-1543) was the sun of a
successful merchant in central Poland. Copernicus
studied to be a physician, which, at the time
included the study of astronomy, because doctors
used astrology to decide on treatments.
Copernicus worked as a deacon in the Church and
spent his time studying
Astronomy. He wrote the first draft of De
Revoluitonibus in 1513, but, because of worries
about how it would be received, he delayed
publication until 1543, when he was on his death
bed.
5
What else was going on at the Beginning of the
16th Century?

• Europe was coming out of the dark ages,
  rediscovering Greek and Roman learning and
  exploring the world.

• Explorers were sailing to Africa and Asia.
  Columbus discovered America while Copernicus was
  studying at the University. Malgalhães
  (Magellan) circumnavigated the globe. All this
  relied heavily on Astronomy.
• Printing was becoming common. A man of modest
  means, like Copernicus, could own books. He had
  2 copies of the Almagest.
• There was an explosion in artistic activity.

6
Michelangelos David1501-1504
da Vincis Mona Lisa 1503-1506
7
Copernicus Solar System

• The Sun is in the center
• Simpler than Ptolemys Model (No need for
  epicycles)
• Circular Orbits are assumed. This will be proved
  wrong.
• More accurate? No, it had about the same
  accuracy.
• Why would we prefer this model to Ptolemys?

From De Revolutionibus

8
Ptolemys Geocentric System, codified in the
Almagest
Figures from Astronomy Today by Chaisson and
McMillan
This is getting complicated.
Link to movie
9
Occams Razor
William of Ockham (1285-1349) was a Franciscan
monk and philosopher who espoused the virtues of
simplicity and poverty in science and in life.
Suggesting that the Pope conform to the latter
got him excommunicated.
One should not increase, beyond what is
necessary, the number of entities required to
explain anything. If you have two theories that
are equally successful in explaining a
phenomenon, the simpler one is better.
The conviction of simplicity persists.
10
Tycho Brahe (1546 1601)
The discovery of a new star
11
Stellar Parallax

• Tycho argued that the new star must be in the
  celestial sphere because it exhibited no
  parallax.
• This discovery showed that the heavens were not
  perfect and unchanging.

12
25 Years of Planetary Observations
Tycho caught the attention of King Frederick II
of Denmark With royal funds, he built the
ultimate observatory. He designed, tested
instruments, compiling the most comprehensive
planetary observations ever, with accuracy of 1,
about 5x better than before.
Uraniborg, Hven complete with wine cellar and
prison
13
Johannes Kepler(1571-1630)
Kepler joined Tycho a year before Tychos death
(1600). Assuming Tychos position, Kepler
inherited the records of Tychos
observations. From this Kepler knew that planets
did not travel on circles and devised a new way
to describe planetary motion.
Kepler searched for a single physical explanation
to planetary motion a force between planets and
the Sun.
14
Kepler aimed to explain Tychos observations
which showed that planets do not move in
circles He noted that planets closer to the Sun
in Copernicus model moved faster than those
further out. A force must therefore act.
Kepler thought it was magnetic Thus he
believed that a simple set of laws existed by
which all planets move.
Influenced by William Gilberts De Magnete
15
Keplers Three Laws

• Planets move about the Sun in elliptical orbits
  with the Sun at one focus.
• The line joining a planet to the Sun sweeps over
  equal areas in equal intervals of time.
• The square of the time of one revolution of a
  planet about the Sun is proportional to the cube
  of the orbits semimajor axis.

16
1. Planets move in elliptical orbits with the
Sun at one focus.
17
2. The line joining the Sun to the planet sweeps
equal areas in equal intervals of time.
Link to movie
18
3. The square of a planets period equals the
cube of its semi-major axis
P2 k a3
P is the period, a is the semi-major axis, k is a
constant which depends on the units of P a.
(For P in years and a in Astronomical Units, k1.)
The farther a planet is from the Sun, the longer
its year
19
Simple Example of P2a3

• Consider a hypothetical planet orbiting the sun
  with a semi-major axis of 4 A.U.
• Let a 4 A.U. (Astronomical Units)
• Then a3 43 A.U.3 64 A.U.3
• P2 64 years2
• P SQRT(P2)SQRT(64) years 8 years
• The period of the planet is 8 years.

20
Keplers Third Law
21
Summary
In the 16th century Europeans began exploring the
planet, navigating by the stars, and renewed
their interest in science and the arts. In
Astronomy this led to the first new theory
describing celestial motions in 1400 years. The
Copernican revolution was a tentative, first step
towards the establishment of the modern
scientific method.