Transcript Presentation: Early Astronomers and Three Rock Stars

Welcome to
Astronomy 1105
Mars from CSU’s Mead Observatory
…And, NO…
It’s NOT Astrology!!!
Stacie and Katie from Spring 2012 Class
First recorded constellations  Sumerians ; before 2000 B.C.
Examples: The Bull, Lion & Scorpion
Some of the same constellations were identified by different cultures,
including the Chinese.
About 600 B.C., Thales of Miletus recorded these and many other
constellations that are still accepted today.
Other activities: Founded geometry, predicted eclipses, sought natural rather than divine explanations
for events.
Predicting the changing seasons was very important for agricultural
societies.
The Egyptians used the heliacal rising of the star Sirius to predict when
the Nile would flood its banks. "Dog Days."
Sirius used to mark the rainy season in other cultures, e.g. the Ethiopian
rainy season causes the Nile flooding!
Thales of Miletus (600 BC)
Greek Astronomy
a) Began with Thales of Miletus ~ 600 B.C.
b) Introduced a change in Worldview.
The New Idea? - The universe could be explained mechanically
(geometrically).
The Greeks observed the 5 planets known from ancient times. (What
were they? Why were they known ?)
Planets  Wanderers or Wandering Stars From the Greek verb for "to wander.“
These planets moved against the background stars, west to east, from
night to night just like the Sun and Moon … most of the time.
Prograde motion - “Normal” West to East motion of planets
with respect to the background stars.
Retrograde motion - Short periods of backward (East to
West) motion. These periods were difficult to explain by the
early astronomers.
The Retrograde of Mars in 2007
Photo by Tunc Tezel – www.twanight.org
Two Greek Model Builders
There were two Greek
philosophers/scientists who gave the
world notable models to explain
motions of objects in the sky
mechanically.
Aristotle - (350 BC)
1. Aristotle (350 B.C.) - Proposed a geocentric model of the Universe
with 55 celestial spheres.
Geocentric - Earth-centered; having the Earth as its center.
(Other texts have different numbers!)
•
The Earth was fixed in the center.
• Other celestial bodies were fixed to concentric spheres and moved
independently.
• The stars were fixed to the outermost sphere. It was responsible for
the motions of all the inner spheres.
• On the outside was the Primum Mobile - [Prime Mover] - It was the
Divine force that caused all motions.
In Aristotle's worldview, the Earth was corrupt and changeable, but the
heavens were perfect and unchanging.
•
Spheres (or circles) represented the perfect shape.
• The spheres were formed from the fifth element, the
"Quintessence." (What were the other four?), the fifth and highest
essence after the four elements of earth, air, fire, and water, thought to
be the substance of the heavenly bodies and latent in all things.
• Problem: Aristotle's spheres did NOT predict future positions
accurately or account for retrograde motion well!
Claudius Ptolemy
(AD 140)
2. Claudius Ptolemy of Alexandria (140 AD)
•
Lived approximately 500 years after Aristotle.
•
Proposed the second great geocentric model.
•
Model also was based on circles, the perfect shape.
• Used Epicycles, along with deferents and equants to explain
retrograde motion.
This Model:
1. Was published in the Almagest
2. Agreed well with observations
3. Accurately predicted the positions of the planets
(…for a LONG time)
4. Lasted for 15 CENTURIES!!
This model survived even though Aristarchus had put forth a Suncentered (Heliocentric) model in 200 B.C.!
The "problem" with Aristarchus's model - No parallax among the
stars! -- The stars were much further away than the Greeks understood.
Meet Eratosthenes (273 BC)
•Greek Scientist
and
Mathematician
•Worked at the
Great Library in
Alexandria,
Egypt.
Meanwhile - Also around the time of Aristotle lived…
Eratosthenes (273 B.C.)
1. Eratosthenes believed that the Earth was round (a sphere).
2. About 1700 years before Columbus!
3. Devised an experiment to estimate the size of the Earth (235 B.C.).
•
He knew that the day of shortest shadows in his home in
Alexandria, Egypt was around June 22 (Summer Solstice).
•Eratosthenes believed the Earth
was spherical.
•He devised an experiment to
estimate its size.
•In Syene, sunlight shown straight
down a well on the summer solstice.
•In Alexandria, a vertical stick cast a
shadow on the same day.
• Eratosthenes had heard/read that in Syene (to the south), on the
“Day of Shortest Shadows,” June 22, sunlight shines straight down a
deep well, and is reflected back up again. That meant these rays would
pass to the center of a round Earth!
•
On the same day in Alexandria, a vertical stick is 8 times higher
than its shadow, creating a 7.2 degree angle.
How many degrees in a circle?
360◦
360º = 7.2º x 50
So, 7.2 degrees was about 1/50 the circumference of the Earth.
The distance to Syene was 5000 stadia (about 800 km)
This meant that the Earth's circumference was 50 x 800 km
C = 40,000 km (Actual value - C = 40,074 km, or only 1% off!)
Using the difference in the angles of the Sun’s rays,
Eratosthenes was able to determine that the distance
between Alexandria and Syene was 1/50 of the
circumference of the Earth.
Hypatia (400 AD)
The last great astronomer of Alexandria.
Hypatia was the first notable woman in the
history of Astronomy and Mathematics
Only historical scraps of evidence
remain of Hypatia. All Hypatia's
work is lost except for its titles
and some references to it. No
purely philosophical work is
known. Only work in mathematics
and astronomy. Based on this
small amount of evidence, some
argue that Hypatia was an
excellent compiler, editor, and
preserver of earlier mathematical
works.
She was killed by a mob during religious unrest in Alexandria.
Then came…
The Dark Ages
…and these lasted a LONG time!
Things didn't change much until around the time of the…
Renaissance - (Began in roughly the late 1300's/ early 1400's)
Nicolaus Copernicus - Poland (1473-1543)
• Grew up & worked in the Church; studied Canon Law
His Uncle was a Bishop
• Educated at the University of Krakow - mathematics & medicine
• Later studied in Italy - began to conceive a new model of the universe
• Advanced a heliocentric, sun-centered model of the universe
Consequences:
1. Readily explained retrograde motion.
2. Demoted Earth to "just" a planet.
3. Stated that all planets move around the Sun in circles (old way of
thinking), although he still used some epicycles.
He had these ideas most of his adult life, but…
Nicolaus Copernicus
(1473-1543)
His ideas were published in De Revolutionibus Orbium Coelestium
(Concerning the revolutions of the heavenly spheres) - 1543
Note the year! He is said to have received a copy of the printed book for
the first time on his deathbed. (He died of a cerebral hemorrhage.)
The term Revolutionary is derived from his book title.
• Remember, this is around the time of Martin Luther (Reformation 1521) and the Inquisition (1481).
The Church had incorporated Aristotelian ideas into its dogma.
Results from this theory:
1.
2.
3.
4.
Neatly explained Retrograde Motion.
Copernicus was able to estimate of the distances to the planets
He also derived the periods of the orbits from the model.
Nicely explained the "strange" motions of Mercury and Venus.
Tycho Brahe
(1546 - 1601)
Tycho Brahe
Uraniborg – Castle of
Astronomy
Let's meet one more of the "Early Astronomers."
Tycho Brahe (1546 - 1601) Danish Astronomer
•
Was born a Nobleman 3 years after the death of Copernicus.
• Believed none of that Copernican nonsense! (Tables of planetary
positions from Copernicus's work incorrectly predicted a conjunction of
Jupiter & Saturn witnessed by Tycho!)
Sometimes referred to as…
1. The greatest naked-eye observer of all time.
But don't get confused. He still used huge instruments to measure the
positions of stars & planets, just not telescopes!
2. Old Brass-Nose! (tell ya' why later.)
•
At age 14 (1560) he witnessed a predicted (partial) eclipse of the
Sun.
Tycho was so impressed by this eclipse that he …
Devoted the rest of his life to the study of celestial motions and positions
Today this field is called astrometry
• At age 20, Tycho lost his nose in a sword duel with a fellow student
over mathematics. He wore a silver and gold nose-piece for the rest of
his life. (Old Brass-Nose!)
•
In 1572, he discovered a "New Star" in Cassiopeia. - Tycho's Star.
(Today referred to as Tycho's Supernova - Radio Source 3C 10; 8000 l.y.)
•
•
In 1576, established Uraniborg on the Island of Hven (Hveen) in
Denmark with the help of the Danish King, Fredrik II.
Here, he made… Observations of unprecedented accuracy.
In 1597, he lost his support. (Quarrel with the new Danish King) He
moved to Prague 2 years later.
•
He was joined in Prague by a new assistant, Johannes Kepler.
(Their relationship was complicated!)
•
He died in 1601.
Tycho Brahe
The Three
Rock Stars
Johannes Kepler (1571 - 1630)
The Origin of Modern Astronomy
Johannes Kepler - (1571 - 1630) German Astronomer & Mathematician
•
Began investigating planetary motion in 1595.
He believed the motions of the planets could be explained geometrically
using the 5 perfect (regular) solids.
1) Pyramid [tetrahedron],
2) Cube,
3) Octahedron,
4) Dodecahedron,
5) Icosahedron.
•
•
four faces
six faces
eight faces
12 faces
20 faces
Joined Tycho as an assistant in 1600
Studied Tycho's tables of planetary motion (as well as other tables)
•
Between 1609 & 1618, published new ideas about the motions of
the planets; became known as Kepler's Laws
(Based on Tycho’s Data Set)
•
In 1609 he published Astronomia Nova (New Astronomy), which
contained Kepler's first two laws of planetary motion.
•
In 1618 (or 1619) he published Harmonices Mundi (Harmonies of
the Universe or World), in which he describes his "third law."
K1… Kepler's First Law - The planets
orbit the Sun in ellipses, with the Sun at
one focus and the other focus empty.
Make sure you can define major and semimajor & minor and semiminor
axes in an ellipse.
Eccentricity (e) = Distance Between Foci ÷
Major Axis
Conic Sections – All allowable orbits
based on K1. Begin with a right, circular
cone and make various slices through it.
Circle (e = 0) - Slice a cone parallel to the
base (perpendicular to the axis).
Ellipse (e < 1) - Slice a cone at an angle
not parallel to the base, but less than an
angle parallel with one side.
Parabola (e = 1) - Slice a cone parallel
with one side.
Hyperbola (e > 1) - Slice a cone parallel
with the axis.
K2… Kepler's Second Law - "The Law of Equal Areas"
The line joining the Sun and a planet sweeps
through equal areas in equal times.
K3… Kepler's Third Law - The square of the
period (P) of revolution is proportional to the cube
of the semimajor axis (R or a) of the ellipse.
Note: the semimajor axis is similar to a “radius” for ellipses that are not very eccentric.
Kepler Pizza Photo courtesy of Don Tillman – www.till.com (All slices have same area!)
Random Picture of ISS and Space Shuttle
Flying in Front of the Sun …Just because it’s cool! 
Galileo Galilei
(1564 - 1642)
Galileo Galilei (1564 - 1642)
•
Italian Astronomer
• Began to relate what was known about physics (on Earth) to what
was known about astronomy.
•
Began to believe in the Copernican system in the 1590's.
• In 1609 - 1610, began to use a telescope to make systematic
astronomical observations of the sky. He was the first to do this!
• He did NOT invent the telescope!! (Probably Dutch eyeglass
makers, first.)
Galileo Galilei (1564 - 1642)
• In 1610, he published Siderius Nuncius (The Starry Messenger).
He reported his telescopic observations:
1.
Could see more stars than without it.
Implication: The true numbers was vast and unknown!
2.
Milky Way "haze" contained individual stars.
Implication: Again, more stars, and previous ideas about the nature of
the Milky Way were incorrect!
3.
Discovered mountains, craters and maria on the Moon.
Implication: The moon was not a perfect sphere; it has "imperfections!"
4.
Discovered the four large moons of Jupiter.
Implication: Something was NOT orbiting the Earth!!!
5.
Sunspots; Saturn's "Ears"; Phases of Venus.
Implication: Something else was NOT spherical and not a star!
All of these discoveries implied:
1) That objects in the heavens were not "perfect," and
2) That Aristotle and Ptolemy were uninformed and thus had no divine
insight.
Galileo's Observations
1) Supported the Copernican Theory.
2) Contradicted the Aristotelian model held by the Roman Catholic
Church.
Remember, Italian philosopher & Copernican Giordono Bruno was
burned at the stake by the Inquisition in 1600!
•
In 1633, Galileo was forced to recant by the Inquisition.
Sir Isaac Newton (1642 - 1727)
Sir Isaac Newton (1642 - 1727)
•
English scientist and mathematician.
•
Born the year Galileo died.
• Among many other things, he derived the basic principles of motion
& gravitation. In order to do this, he had to invent calculus!
• Published his ideas in The Principia (1687). Working with Edmund
Halley.
• Was the first to describe Universal Gravitation, on Earth as well as
in space!
•Gravity is always attractive.
•Fg  m1m2 Force of gravity is proportional to the product of the masses.
•Fg  1/d2 Force of gravity goes as the inverse square of the distance.
•Fg = Gm1m2/d2 Universal Law of Gravitation
Sir Isaac Newton (1642 - 1727)
Newton's Three Laws of Motion
1. Objects tend to stay at rest or in a state of uniform motion unless
acted upon by an outside force. Law of Inertia
2. The acceleration experienced by an object is proportional to the
force applied to the object and inversely proportional to its mass.
F = ma
Law of Force
3. For every action there is an equal and opposite reaction.
Rockets & Balloons
He was able to derive Kepler's Laws from these Laws and find the
masses of the planets and the Sun.