Transcript Chapter3 - The Science of Astronomy-ppt

Chapter 3
The Science of Astronomy
Everyday Science
• Scientific Thinking is a fundamental part of
human nature.
• Scientists apply the scientific method to
their inquiries about the universe.
Ancient Observations
• Central Africa: c. 6500 B.C. People use the
observations of the moon to predict the
weather.
Graph depicts the annual rainfall pattern in central
Nigeria, characterized by a wet season and a dry
season.
Modern measures of time still reflect
their ancient astronomical roots.
• 24 hour day – the time it takes the Sun to circle our sky.
• Month – comes from the lunar cycle.
• Calendar Year – Based on the cycle of the seasons.
• Days of the week – named after the seven “naked-eye”
objects that appear to move among the constellations.
(Sun, Moon and five planets)
• At night, the position and phase of the Moon give an
indication of the time.
The Seven Days of the Week and the
Astronomical Objects They Honor
Determining the time of day
• In the daytime, ancient peoples could
tell the time of day by observing the
Sun’s path through the sky.
The ancient Egyptians used huge obelisks as
simple clocks/ (Sundials).
Ancient Egyptian obelisk which now resides in St.
Peter’s Square, Vatican in Rome.
Determining the Time of Year
• Many cultures built structures to help them
mark the seasons.
• A good example of this is Stonehenge.
Stonehenge
Reconstruction
c. 1550 B.C.
The Sun Dagger– Chaco Canyon, New Mexico
The dagger
pierces the
center of
the carved
spiral each
year at
noon on the
summer
solstice
Blue Moon:
The second full moon to occur in a particular
calendar month.
See link below for more info about Blue Moons.
Interactive Astronomy Pages
Lunar Cycles
• Many ancient cultures used the lunar cycle as the
basis of lunar calendars.
• Metonic cycle:
– The ancient Greek astronomer Meton (432 B.C.)
observed that the dates of the lunar cycle repeat every 19
years.
• Other cultures based their calendars on their ability
to predict eclipses:
• Babylonian Calendar
• Mayan Calendar
Observation of Planets and Stars
• Many cultures made careful observations of the
planets and the stars.
• Mayan observatories of Central America had
windows placed to allow for observations of
Venus.
In the desert regions of
Peru, many large
figures of animals may
have represented
constellations to the
Incas who lived there.
The Big Horn
Medicine Wheel in
Wyoming may have
been related to the
month for the Native
Americans.
From Observation to Science
• Ancient Chinese
Astronomers kept very
detailed records of
astronomical
observations
beginning 5,000 years
ago.
• They were the first to
record an observation
of a Supernova
explosion, which we
see today as the Crab
Nebula.
• In the Americas, the Mayans had
developed a modern system of
numbers and mathematics, which
included the invention of the concept
of zero.
• It appears that virtually all cultures
employed scientific thinking to varying
degrees.
The Modern Lineage
• 3000 B.C. The establishment of civilization
occurred in Egypt and Mesopotamia.
• 2700-2100 B.C. Egyptians build the Great
Pyramids.
• 500 B.C. Greece rises as a military power.
• 330 B.C. Alexander the Great expands the Greek
empire throughout the middle east.
• As a student of Aristotle, Alexander had a great
interest in science and education.
Map of the Middle East in Ancient Times
• 300 B.C. The Library of Alexandria is
established as the leading center of
knowledge, housing more than half a
million books.
• ~ 415 A.D. The destruction of the
library of Alexandria, along with the
loss of most of the knowledge stored
there.
The Great Hall in the Library of Alexandria (Rendering)
• One of the most important scientific
contributions from ancient Greece was the
idea of creating models to represent natural
phenomena.
• Models are still used today to help us in
understanding natural phenomena.
• Claudius Ptolemy (100-170)A.D. developed
an Earth centered (geocentric) model of the
universe that included the motions of the
Sun, moon, and planets.
Ptolemaic Model of the Universe
• All heavenly motions proceed in perfect circles.
• To explain retrograde motion, Ptolemy maintained
that each planet moved along a small circle that, in
turn, moved around a larger circle.
• This allowed for the observed westward
(retrograde) motion that some planets exhibited.
• The large circular orbit around the Earth was
called the “Deferent”
• The smaller circular motion along a “deferent”
was called an epicycle.
Ptolemy’s model of the Solar
System/Universe
Epicycle
Deferent
The Copernican Revolution
• 1543 Copernicus publishes
De Revolutionibus Orbium
Caelestium, “Concerning the
Revolutions of the heavenly
Spheres”.
• Copernicus modifies the
Ptolemaic model as
noticeable discrepancies
become more apparent with
the improvements in
observational astronomy.
Nicholas Copernicus
(1473-1543)
The Copernican Model of the Solar
System
• The Sun and not the Earth, is at the center
of the solar system.
• The earth does move, and like the other
planets, orbits the sun.
• The orbital paths follow perfect circles.
• Made detailed naked eye
observations of the motions of the
planets.
• Coined the term NOVA for the
observation of a supernova (Nova
means “New Star”)
• Showed that comets were distant
objects rather than being
phenomena of the Earth’s
atmosphere, as argued by
Aristotle.
• In the course of 30 years, he had
amassed the best astronomical
data of the day It was accurate to
within 1 arc-minute.
Tycho Brahe (1546-1601)
Johannes Kepler (1571-1630)
• A mathematician and a man of faith, who believed
that understanding the geometry of the heavens
would bring him closer to God.
• Inherited Tyco Brahe’s astronomical data.
• With his mathematical skills, Kepler spent
20 years of his life trying to develop a consistent
model to describe planetary motion.
• His efforts culminated in what is known today as
Kepler’s Three Laws of Planetary Motion.
Kepler’s First law of planetary Motion
• The orbit of each planet about the Sun is an
ellipse with the Sun at one focus.
Major Axis
Minor Axis
Kepler’s Second Law of Planetary Motion
• As a planet moves around its orbit, it
sweeps out equal areas in equal times.
Kepler’s Third Law of Planetary Motion
• The square of a planet’s orbital period is
proportional to the cube of its semi-major
axis.
(Orbital period in years)2 = (Semi-major Axis in AU)3
P2 = a3
• The Copernican view of the solar system and Kepler’s
three laws of planetary motion were very successful in
explaining and predicting observations.
• However, due to the degree to which the Ptolemaic
model was ingrained in the current thinking of the day,
major objections were put forth with regard to the new
Copernican/Keplerian model.
Main Objections to Copernican/Keplerian View
• The Earth could not be moving because if it did,
objects such as birds, falling stones, and clouds would
be left behind as the Earth moved along its way.
• The idea of noncircular orbits contradicted the ancient
Greek belief that the heavens must be perfect and
unchanging.
• Stellar parallax should be detectable if the Earth orbits
the Sun. (True, but difficult to detect)
Galileo’s defuses all objections
Galileo (1564- 1642)
• Galileo performed careful experiments on the
motions of moving bodies and showed that a moving
object remains in motion unless a force acts to stop
it or change its direction.
• Tycho’s observations of a comet and supernova
showed that the heavens could change.
• The lack of noticeable stellar parallax was simply
due to the fact that the stars were much farther away
than anyone had previously thought.
Galileo Invents the Telescope
Galileo observes four
moons clearly
orbiting Jupiter.
This shows that
objects do orbit
planets other than the
Earth.
One of Galileo’s
Refracting Telescopes
Phases of Venus
• Galileo observes that Venus goes through phases
much like the moon does. Only a Heliocentric
model of the solar system can account for all
observed phases.
Geocentric Model cannot
account for all observed
phases
Heliocentric model can
account for all observed
phases
Galileo’s Other Telescopic Discoveries
• Craters, mountains and cliffs on the Moon.
• Sunspots
End Of Section