Download I. Early History of Astronomy

I. Early History of Astronomy
A. Ancient Greeks
1. Used philosophical
arguments to explain
natural phenomena
2. Also used some
observational data
3. Most ancient
Greeks held a
geocentric (Earthcentered) view of the
universe
4. Air, Earth, Fire,
Water
5. Aristotle-spherical
earth
Geocentric animation
I. Early History of Astronomy
a. "Earth-centered" view
1. Earth was a motionless
sphere at the center of the
universe
2. Stars were on the
celestial sphere
a. Transparent, hollow
sphere
b. Celestial sphere
turns daily around Earth
b. Seven heavenly bodies
1. Changed position in sky
2. The seven wanderers
included the
a. Moon
b. Mercury
c. Venus
d. Sun
e. Mars
f. Jupiter
g. Saturn
Aristotle
I. Early History of Astronomy
6. Anaxagoras (500-450 BC)moonlight physics
7. Aristarchus (312–230 B.C.)
was the first Greek to
profess a Sun-centered,
or heliocentric, universe
He also calculated relative
sizes and distances of the
sun,earth, moon
I. Early History of Astronomy
8. Eratosthenes
(276-194 BC):
a. 1st to accurately
measure the earth’s
circumference using a
gnomon and the sun.
(250,000 stadia)
b. Error of only
~500 miles
I. Early History of Astronomy
9. Hipparchus (190120BC):
a. logged ~ 850 star
locations and star
brightness (6 different
magnitudes)
b. Great mathematician
(trig)
These are
the
apparent
magnitudes
of the
bright
objects
seen in the
sky.
I. Early History of Astronomy
10. Planets exhibit an
apparent westward drift
a. Called
retrograde motion
b. Occurs as
Earth, with its
faster orbital
speed,
overtakes another
planet
animation
Retrograde movement
I. Early History of Astronomy
11. Ptolemaic system
(Claudius Ptolemy)
a. A.D. 141, The Almagest
b. Geocentric model
c. To explain retrograde
motion, Ptolemy used two
motions for the planets
1. Large orbital circles,
called deferents, and
2. Small circles, called
epicycles
Animation of epicycles and deferents
I. Early History of Astronomy
…Ptolemy’s Epicycles and Deferents…
I. Early History of Astronomy
…Ptolemy’s retrograde motion…
I. Early History of Astronomy
…a model built to explain Retrograde Motion in both a
Geocentric and Heliocentric design…
RetroLink
I. Early History of Astronomy
B. Birth of modern astronomy
1. 1500s and 1600s
2. Five noted scientists
a. Nicolaus Copernicus
(1473–1543)
1. Concluded Earth was
just a planet
2.
Constructed
a
model of the solar
system that put the
Sun at the center,
but he used circular
orbits for the planets
3. Heliocentric Solar
System
4. Ushered out old
astronomy
5. De Revolutionibus
I. Early History of Astronomy
b. Tycho Brahe (1546–
1601)
1. Precise observer
2. Tried to find stellar
parallax: the apparent
shift in a star's position
due to the revolution of
Earth
3. Did not believe in the
Copernican system
because he was unable to
observe stellar parallax
Animation of
different
systems
I. Early History of Astronomy
Tycho Brahe (1546–1601)
4. Great instrument
maker
Cassiopeia…1572
Tycho’s Supernova
Tycho Crater on the
Moon
The Quadrant
I. Early History of Astronomy
c. Johannes Kepler
(1571–1630)
1. Ushered in new
astronomy
2. Planets revolve
around the Sun
3. Student of
Tycho Brahe
4. Strong
mathematician
I. Early History of Astronomy
5. Three laws of planetary motion
a. Orbits of the planets are elliptical
b. Planets revolve around the Sun at varying speed
(Faster at perihelion…..slower at aphelion)
c. There is a proportional relation between a
planet's orbital period and its distance to the Sun
(measured in astronomical units (AUs)—one AU
averages about 150 million kilometers, or 93
million miles) P2=a3
I. Early History of Astronomy
…What is an Ellipse?...
I. History of Early Astronomy
I. Early History of Astronomy
..the properties of an ellipse…
I. Early History of Astronomy
Kepler’s 3 Laws:
#1: All orbits are elliptical……………..e is eccentricity
As “e” approaches 0, the
orbit becomes more
circular!
Icarus’ orbit
I. Early History of Astronomy
Kepler’s 3 Laws:
#2: Equal Area Law
animation
This implies a planet
moves faster at
perihelion and slower
at aphelion!
I. Early History of Astronomy
Kepler’s 3 Laws: #3: P2 (years) = a3 (AU)
For Earth: Period is 1 year
a is 1 AU
Therefore (1)2=(1)3
For Jupiter: Period is 11.86 years
a is 5.20 AU
Therefore: (11.86)2 = (5.20)3
140.6 = 140.6
I. Early History of Astronomy
…Kepler’s 3 Laws of Planetary Motion…
I. Early History of Astronomy
d. Galileo Galilei
(1564–1642)
1. Supported
Copernican theory
2. Used experimental
data
3. Used an
astronomical telescope
in 1609
4 Galilean
Satellites:
Io, Europa,
Ganymede,
Callisto
I. Early History of Astronomy
4. Galileo's discoveries
using the telescope
a. Four large
moons of
Jupiter
b. Planets
appeared as
disks
c. Phases of
Venus
d. Features on
the Moon
e. Sunspots
and sun’s
rotation
I. Early History of Astronomy
s
I. Early History of Astronomy
5. Tried and convicted by the Inquisition…died
under house arrest
6. In 1992, 350 years later, Pope John Paul II
officially declared Galileo innocent.
7. Galileo died, blind and under house arrest, on
January 8, 1642.
On Christmas Day of that same year, born
was…………
I. Early History of Astronomy
e. Sir Isaac Newton
(1643–1727)
1. Law of universal
gravitation
2. Proved that the
force
of
gravity
combined with the
tendency of a planet
to remain in straightline motion results in
the elliptical orbits
discovered by Kepler
3. 3 laws of motion
(inertia…1st law)
4. Mass vs Weight
5. Principia
Orbital animation
Halley’s
Comet
I. Early History of Astronomy
…What is Gravity?...
I. Early History of Astronomy
…What is Gravity?...
I. Early History of Astronomy
…What is gravity?...
I. Early History of Astronomy
…What is Gravity?...
Zero G drink
I. Early History of Astronomy
…Orbital Movement…
Link
I. Early History of Astronomy
…A brief timeline review………