Transcript History of Astronomy

History of Astronomy
“Progress in science is often slow and
intermittent and may require a great deal of
patience before significant progress is made”
(McMillan 18).
Aristotle





Greek Philosopher
384-322 B.C.
Geocentric: Earth
center of the universe
Taught the perfect
form: Circle
Pros: Described the
moon and sun’s orbit
Cons: variations in
planetary brightness
and planets orbits
phillwebb.net
Claudius Ptolemaeus
Ptolemy 40 AD
 Ptolemaic model

◦ Described 5 planet
orbits well

Building off
Aristotle's version
and what observers
had observed in the
sky dealing with
planetary motion
reocities.com
Claudius Ptolemaeus
ptolemy.berkeley.edu
Aristarchus of Samos
Lived: 310-230 B.C.
 All planets, including Earth, revolve around
the sun.
 Earth rotates on its axis once each day
 Why his ideas weren’t accepted: Politics,
Aristotle’s ideas won the popular vote

“Usually one generation of
scientists can bring sufficient
objectivity to bear on a problem,
though some especially
revolutionary concepts are so
swamped by tradition, religion, and
politics that more time is need”
(McMillan 31).
Nicholas Copernicus

Polish Cleric
◦ 16th century

Copernican Revolution
◦ All planets orbit the sun
◦ Explained planets orbits and variation in planetary
brightness
◦ Wrote of his findings, but claimed them as only a
mathematical hypothesis
 Keep him out of trouble with the church
◦ Never excepted during his life time
 Went against the religious view points at the time
 Contradicted conventional wisdom: didn’t match Aristotle
thinkers.
Nicholas Copernicus
indiamart.com
Diagram of the
Copernican
system, from De
Revolutions
http://galileo.rice.edu/sci/theories/copernican_system.ht
ml
marcdatabase.com
Galileo Galiei


Italian mathematician
and philosopher
Used the brand-new
technology to further
humans understanding
= telescope
◦ Telescope was invented
in Holland in early 17th
century

Performed
experiments to test his
ideas
◦ ‘Father of experimental
science’
quotationsbook.com
Galileo’s Discoveries
Moon has mountains, valleys, and craters
 Sun has imperfections-dark blemishes
now known as sunspots
 Sun rotates approximately once per
month around an axis roughly
perpendicular (right angle) to the Earth’s
orbit.
 Jupiter’s moon (4 of them)
 Venus show a complete cycle of phases,
similar to the moon

Galileo’s Popularity





His ideas were opposite to what science thought at that time
1610 published his findings agreeing with Copernican theory.
1616 his ideas were judged contrary to accepted belief of
that time
Both his and Copernicus were banned by the ‘Church’
Told to abandon his astronomical pursuits
◦ Which he didn’t

“These actions brought Galileo into direct conflict with the
Church. The Inquisition forced him, under threat of torture,
to retract his claim that Earth orbits the Sun, and he was
placed under house arrest in 1633” (McMillan 30).
◦ It wasn’t until 1992, did the ‘Church’ publicly forgave Galileo
‘crimes’
Tycho Brahe





1546-1601, Denmark
Studied astrology, alchemy, and medicine
Kept meticulous records of stars, planets,
and celestial events.
He move to Prague, after a falling out with
the Danish courts
There he hired Kepler to find a theory that
could explain Brahe’s planetary data
◦ Year later Brahe died and Kepler inherited Brahe
potion (Imperial Mathematician of the Holy
Roman Empire) and possession
Johannes Kepler
16th century German
mathematician and
astronomer
 Took him 29 years to
try and find an
unifying principle to
explain the motions
of the planets

◦ Data was collected by
Brahe
libwebspace.library.cmu.edu
Kepler’s Laws
The orbital paths of the
planets are elliptical with the
Sun at one focus
I.
◦
An imaginary line connecting
the Sun to any planet sweeps
out equal areas of the ellipse in
equal intervals of time.
II.
◦
◦
III.
Ellipse is a flattened circle, a
circle is a special kind of ellipse
When the planet is closer to
the Sun it must move faster
then it is further away
This applies to any orbiting
object
astro.psu.edu
The square of a planet’s orbital
period is proportional to the
cube of its semi-major axis
hyperphysics.phy-astr.gsu.edu
Isaac Newton
17th century British
physicist/mathematician
 Newtonian Mechanics

◦ 3 basic laws of motion, the
laws of universal
gravitation, and a little
calculus
en.wikipedia.org
Newton’s 1st Law
Inertia: the tendency for an object to keep
moving in the same direction and speed
unless acted upon by an outside force.
 More mass = greater inertia and the
more force is needed to change its
motion

Newton’s 2nd Law

The acceleration of an object is directly
proportional to the net applied force and
inversely proportional to the object mass
◦ Greater force or smaller mass = increase
acceleration
◦ F=ma
Newton’s 3rd Law

To every action there is an equal and
opposite reaction
Laws of Universal Gravitation
Gravitational force: things with mass
exerts attraction on other masses
 “ The mutual gravitational attraction of
the Sun and the planets, as expressed by
Newton’s law of gravity, is responsible for
the observed planetary orbits” (McMillan
37).

◦ The Sun pulls the planets changing the planets
forward motion into a curved path
Newton’s revision to Kepler’s Laws
The orbit of a planet around the Sun is an
ellipse having the center of mass of the
planet-Sun system at one focus
I.
◦
III.
The center of mass of two objects about the
same size is outside either object. However if
one object is larger then the other the center
of mass shifts towards the larger object.
Changed the math to use the combined
mass of the two object, which made it
more correct and also allowed it to be
used outside our solar system