History of Astronomy
Dec 16, 2015
“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 PtolemaeusPtolemy 40 ADPtolemaic model
◦ Described 5 planet orbits well
Building off Aristotle's version and what observers had observed in the sky dealing with planetary motion
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Aristarchus of SamosLived: 310-230 B.C.All planets, including Earth,
revolve around the sun.Earth rotates on its axis once
each dayWhy 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 CopernicusPolish Cleric
◦ 16th centuryCopernican 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
http://galileo.rice.edu/sci/theories/copernican_system.html
Diagram of the Copernican system, from De Revolutions
Galileo GalieiItalian mathematician
and philosopherUsed 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
marcdatabase.com
Galileo’s DiscoveriesMoon has mountains, valleys, and
cratersSun has imperfections-dark blemishes
now known as sunspotsSun 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 Brahe1546-1601, DenmarkStudied astrology, alchemy, and medicineKept meticulous records of stars, planets,
and celestial events.He move to Prague, after a falling out with
the Danish courtsThere 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 Kepler16th 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 LawsI. The orbital paths of the
planets are elliptical with the Sun at one focus
◦ Ellipse is a flattened circle, a circle is a special kind of ellipse
II. An imaginary line connecting the Sun to any planet sweeps out equal areas of the ellipse in equal intervals of time.
◦ When the planet is closer to the Sun it must move faster then it is further away
◦ This applies to any orbiting object
III. The square of a planet’s orbital period is proportional to the cube of its semi-major axis
astro.psu.edu
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 LawInertia: 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 LawThe 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
Laws of Universal GravitationGravitational 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 LawsI. The orbit of a planet around the Sun is
an ellipse having the center of mass of the planet-Sun system at one focus
◦ 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.
III. 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