By Ken Journigan Independence High Astronomy The History of Astronomy The History of Astronomy.

By Ken JourniganBy Ken JourniganIndependence High AstronomyIndependence High Astronomy

The History The History of of

AstronomyAstronomy

Astronomical HistoryAstronomical History

A very complete story of A very complete story of astronomy is told in its astronomy is told in its

history. The men and women history. The men and women of astronomical history are of astronomical history are

synonymous with the synonymous with the historical evolution of this historical evolution of this

observational science.observational science.

Universal ModelsUniversal Models

TheThe

Geocentric Model Geocentric Model SupportersSupporters

The Geocentric Model of the The Geocentric Model of the UniverseUniverse

With one mere exception (to be With one mere exception (to be named later), ancient astronomers named later), ancient astronomers placed the Earth at the center of the placed the Earth at the center of the known Universe. This Universal known Universe. This Universal Model was known as the Model was known as the Geocentric ModelGeocentric Model. “Geo” meaning . “Geo” meaning Earth and “centric” meaning Earth and “centric” meaning centered.centered.

Aristotle (Aristotle (384 BC384 BC – – March 7March 7, , 322 BC322 BC) )

Aristotle was an Aristotle was an ancient Greekancient Greek philosopherphilosopher, a , a student of student of PlatoPlato and teacher of and teacher of Alexander the GreatAlexander the Great. Aristotle had a strong . Aristotle had a strong influence, and his teachings carried great influence, and his teachings carried great weight. He promoted the geocentric model. weight. He promoted the geocentric model. According to Aristotle the cosmos were According to Aristotle the cosmos were composed of five fundamental properties composed of five fundamental properties

Earth Earth Air Air Water Water Fire Fire The spherical shells of The spherical shells of heavenly bodies with Earth heavenly bodies with Earth at the center at the center

AristotleAristotle

Aristotle believed that everything in the Aristotle believed that everything in the regions outside the Earth was perfect and regions outside the Earth was perfect and eternally unchanging. All objects in the eternally unchanging. All objects in the heavens were supposed to be perfect heavens were supposed to be perfect circles, except for stars, which were circles, except for stars, which were featureless points of light.featureless points of light.

AristotleAristotle

Aristotle’s beliefs about the Aristotle’s beliefs about the geocentric model of the universe geocentric model of the universe would pervade astronomy to such an would pervade astronomy to such an extent, that they would not be extent, that they would not be challenged for another 1500 years.challenged for another 1500 years.

Plato and AristotlePlato and Aristotle

The Greek Astronomer The Greek Astronomer HipparchusHipparchus

Hipparcus (c. 190 BCE--c. 120 BCE) was born in Nicaea, a Hipparcus (c. 190 BCE--c. 120 BCE) was born in Nicaea, a city in what is now Turkey. In the year 135 BCE, he was city in what is now Turkey. In the year 135 BCE, he was stargazing and saw a bright point of light he didn't recognize.stargazing and saw a bright point of light he didn't recognize.

This star appeared inThis star appeared in

the constellation Scorpio.the constellation Scorpio.

It turned out to be a It turned out to be a

supernova. This disprovedsupernova. This disproved

Aristotle’s idea of the Aristotle’s idea of the

perfect, unchanging Universeperfect, unchanging Universe


Developed the first catalog of stars Developed the first catalog of stars Developed a magnitude scale Developed a magnitude scale

where 1 represented the brightestwhere 1 represented the brighteststars and 6 represented thestars and 6 represented the

dimmest stars.dimmest stars. Determined the precession Determined the precession

of Earth based on recordsof Earth based on records from the past and compared from the past and compared

it to his own observations it to his own observations

The Greek Astronomer The Greek Astronomer HipparchusHipparchus Hipparchus had a problem making his Hipparchus had a problem making his

star chart. It was easy enough to map star chart. It was easy enough to map the surface of the Earth, because the the surface of the Earth, because the Earth has landmarks: rivers, Earth has landmarks: rivers, mountains, cities--places of known mountains, cities--places of known location, to which other places can be location, to which other places can be compared. The sky, however, has no compared. The sky, however, has no landmarks, just the stars themselves. landmarks, just the stars themselves. Hipparchus decided to invent Hipparchus decided to invent "landmarks" of his own. He picked one "landmarks" of his own. He picked one point in the sky and drew imaginary point in the sky and drew imaginary lines radiating out from it, like the lines radiating out from it, like the spokes of a wheel. Then he drew circles spokes of a wheel. Then he drew circles around this central point which grew around this central point which grew larger and larger. larger and larger.


This made a grid around the sky, on which This made a grid around the sky, on which Hipparchus could locate any star he wanted. Hipparchus could locate any star he wanted. This idea soon improved Earthly map-making This idea soon improved Earthly map-making as well: the modern lines of longitude and as well: the modern lines of longitude and latitude come directly from Hipparchus's latitude come directly from Hipparchus's method of mapping the sky. method of mapping the sky.

Instead of locating stars on the "celestial Instead of locating stars on the "celestial sphere" (the entiresphere" (the entire

area visible around the Earth), area visible around the Earth), later map-makers drew later map-makers drew gridlines on their chartsgridlines on their charts of the Earth's sphere. of the Earth's sphere.

Eratosthenes and Size of the Eratosthenes and Size of the EarthEarth

About 200 BC, About 200 BC, EratosthenesEratosthenes used Aristotle's used Aristotle's ideas to calculate the size of the Earth. On a ideas to calculate the size of the Earth. On a certain day of the year, observers at Syene, certain day of the year, observers at Syene, Egypt saw the sun directly overhead. Egypt saw the sun directly overhead. Observers at other locations (Alexandria, Observers at other locations (Alexandria, Egypt) saw the sun at an angle on that day. Egypt) saw the sun at an angle on that day. The angular displacement was measured. The angular displacement was measured.

Using simple geometry, he Using simple geometry, he calculated the circumference calculated the circumference and the radius of the Earth. and the radius of the Earth. The result was within 1 percent The result was within 1 percent accuracy of the figure known today. accuracy of the figure known today.

PtolemyPtolemy

Ptolemy’sPtolemy’s full Latin name was full Latin name was Claudius PtolemaeusClaudius Ptolemaeus (fl. AD 127- (fl. AD 127-145, Alexandria), He was an ancient 145, Alexandria), He was an ancient astronomer, geographer, and astronomer, geographer, and mathematician who considered the mathematician who considered the Earth the center of the universe Earth the center of the universe

(the "Ptolemaic system"). (the "Ptolemaic system").

Virtually nothingVirtually nothing

is known about his life.is known about his life.

The Ptolemaic Model The Ptolemaic Model

The Ptolemaic model accounted for the The Ptolemaic model accounted for the apparent motions of the planets in a apparent motions of the planets in a very direct way, by assuming that each very direct way, by assuming that each planet moved on a small sphere or planet moved on a small sphere or circle, called an epicycle, that moved on circle, called an epicycle, that moved on a larger sphere or circle, called a a larger sphere or circle, called a deferent. The stars, it was assumed, deferent. The stars, it was assumed, moved on a celestial sphere around the moved on a celestial sphere around the outside of the planetary spheres.outside of the planetary spheres.

The EpicycleThe Epicycle

http://physics.syr.edu/courses/java/dhttp://physics.syr.edu/courses/java/demos/kennett/Epicycle/Epicycle.htmlemos/kennett/Epicycle/Epicycle.html

The idea of the epicycle was The idea of the epicycle was incorporating into Ptolemy’s incorporating into Ptolemy’s universal model in order to explain universal model in order to explain retrograde motionretrograde motion

Prograde Versus Prograde Versus Retrograde MotionRetrograde Motion

Prograde Motion: The regular east Prograde Motion: The regular east to west migration of celestial bodies to west migration of celestial bodies across the sky.across the sky.

Retrograde Motion: The irregular Retrograde Motion: The irregular and periodic transit of planets across and periodic transit of planets across the sky from west to east.the sky from west to east.

Universal ModelsUniversal Models

TheThe

Heliocentric Model Heliocentric Model SupportersSupporters

The Heliocentric ModelThe Heliocentric Model HeliocentricHeliocentric (sun-centered) model (sun-centered) model

More accurately accounted for all More accurately accounted for all observations of the movement of the sun observations of the movement of the sun and the moon, and the planets, and the and the moon, and the planets, and the stars stars

were good predictors of future positions were good predictors of future positions of celestial bodies; models were verifiable of celestial bodies; models were verifiable

simplicity (Occam's Razor or the simplicity (Occam's Razor or the Principle of Parsimony) - as few Principle of Parsimony) - as few assumptions or rules as possible; no assumptions or rules as possible; no contradictions. contradictions.

Heliocentric ModelHeliocentric Model

Aristarchus of SamosAristarchus of Samos, a Greek , a Greek about 310-230 BC, had a about 310-230 BC, had a heliocentric model. He proposed heliocentric model. He proposed that all of the planets, including that all of the planets, including Earth revolved around the Sun, Earth revolved around the Sun, and that the Earth rotates on its and that the Earth rotates on its axis once a day. His ideas did axis once a day. His ideas did not gain widespread acceptance not gain widespread acceptance during his lifetime.during his lifetime.

Aristarchus of SamosAristarchus of SamosAristarchus was the first person to Aristarchus was the first person to give the solar system scale.give the solar system scale.

Nicholaus Copernicus and the Nicholaus Copernicus and the Revival of the Heliocentric Revival of the Heliocentric

Universe.Universe. Nicholaus Copernicus Nicholaus Copernicus was a Polish was a Polish

cleric (1473-1543) that lived around cleric (1473-1543) that lived around 1500. He was dissatisfied with the 1500. He was dissatisfied with the complexity of the geocentric model. complexity of the geocentric model. His beliefs would ultimately get him His beliefs would ultimately get him in trouble with the Church. in trouble with the Church.


Universe.Universe. His ideas included:His ideas included:

Sun is at the center of the universe, motionless; Sun is at the center of the universe, motionless; stars are motionless around the edge stars are motionless around the edge

Planets all revolve around the sun (6 total Planets all revolve around the sun (6 total including Earth) including Earth)

Moon revolves around Earth Moon revolves around Earth Earth rotates on axis causing apparent daily Earth rotates on axis causing apparent daily

motion of the heavens motion of the heavens Earth revolves around sun causing sun's annual Earth revolves around sun causing sun's annual

movements movements Retrograde motion of planets is due to relative Retrograde motion of planets is due to relative

planetary motions planetary motions Planetary orbits are perfect circles Planetary orbits are perfect circles


Universe.Universe.Copernicus was the first to Copernicus was the first to accurately determine the relative accurately determine the relative distances of the planets from the distances of the planets from the sun. sun.

Planetary Distances Planetary Distances According to CopernicusAccording to Copernicus

PlanetPlanet Copernican DistanceCopernican Distance Real DistanceReal DistanceMercuryMercury 0.38 AU0.38 AU 0.39 AU0.39 AUVenusVenus 0.75 AU0.75 AU 0.72 AU0.72 AUEarthEarth 1.00 AU1.00 AU 1.00 AU1.00 AUMarsMars 1.52 AU1.52 AU 1.52 AU1.52 AUJupiterJupiter 5.22 AU5.22 AU 5.20 AU5.20 AUSaturnSaturn 9.17 AU9.17 AU 9.54 AU9.54 AU

Copernican views marked the beginning of Copernican views marked the beginning of the modern era of astronomy.the modern era of astronomy.

Tycho BraheTycho Brahe

Over a 20 year period of time, Tycho Over a 20 year period of time, Tycho Brahe made consistent observations Brahe made consistent observations which supported the heliocentric which supported the heliocentric theory proposed earlier by Copernicus. theory proposed earlier by Copernicus. These observations were made using These observations were made using only a compass andonly a compass and

a sextant.a sextant.

Brahe catalogued Brahe catalogued

over 1000 stars. over 1000 stars.

Kepler's First LawKepler's First Law

The orbit of each planet is an The orbit of each planet is an ellipseellipse with the sun at one focus.with the sun at one focus.

Kepler's Second LawKepler's Second Law

The line segment joining a planet to The line segment joining a planet to the sun sweeps out equal areas in the sun sweeps out equal areas in equal time intervalsequal time intervals. .

Kepler's Third LawKepler's Third Law

The square of the period of The square of the period of revolution of a planet about the sun revolution of a planet about the sun is proportional to the cube of the is proportional to the cube of the semi-major axis of the planet’s semi-major axis of the planet’s elliptical orbit.elliptical orbit.

Kepler's LawsKepler's Laws Kepler provided us with a tool, accurate Kepler provided us with a tool, accurate

even by today’s standards, to understand even by today’s standards, to understand the mechanical universe and the orbital the mechanical universe and the orbital nature of the planets.nature of the planets.

The only remaining question, was The only remaining question, was why did why did the planets move the way they didthe planets move the way they did??

The answer to that question could be The answer to that question could be provided by only one man; arguably the provided by only one man; arguably the greatest scientist the world has ever greatest scientist the world has ever seen…….seen…….

Sir Isaac NewtonSir Isaac Newton

……But first, what about But first, what about Galileo?Galileo?

Galileo GalileiGalileo Galilei

1564 - 16421564 - 1642

Galileo GalileiGalileo GalileiHis observations included:His observations included: First to use the telescope for observationsFirst to use the telescope for observations Mountains on the Moon.Mountains on the Moon. The Galilean moons of Jupiter.The Galilean moons of Jupiter. The phases of Venus.The phases of Venus. Saturn and its rings (though he did Saturn and its rings (though he did

not understand why they periodicallynot understand why they periodicallydisappeared).disappeared).

Sunspots.Sunspots.

Galileo GalileiGalileo Galilei Convicted of heresy, Galileo was placed under Convicted of heresy, Galileo was placed under

house arrest for the remainder of his life, a house arrest for the remainder of his life, a gentle punishment for any individual gentle punishment for any individual convicted during the Inquisition. convicted during the Inquisition.

On 31 October 1992, 350 years after Galileo's On 31 October 1992, 350 years after Galileo's death, Pope John Paul II gave an address on death, Pope John Paul II gave an address on behalf of the Catholic Church in which he behalf of the Catholic Church in which he admitted that errors had been made by the admitted that errors had been made by the theological advisors in the case of Galileo. theological advisors in the case of Galileo. The Church however never admitted that they The Church however never admitted that they were wrong in declaring Galileo a heretic!were wrong in declaring Galileo a heretic!

Sir Isaac Newton (1642-Sir Isaac Newton (1642-1727)1727)

Sir Isaac NewtonSir Isaac Newton Newton’s first major publication Newton’s first major publication

regarded his invention, design and regarded his invention, design and construction of the first reflecting construction of the first reflecting (or Newtonian) telescope.(or Newtonian) telescope.

Eliminated chromatic aberration.Eliminated chromatic aberration.

Sir Isaac NewtonSir Isaac Newton In 1684, three members of the Royal Society, In 1684, three members of the Royal Society,

Sir Christopher Wren, Robert Hooke and Sir Christopher Wren, Robert Hooke and Edmond Halley, argued as to whether the Edmond Halley, argued as to whether the elliptical orbits of the planets could result elliptical orbits of the planets could result from a gravitational force towards the sun from a gravitational force towards the sun proportional to the inverse square of the proportional to the inverse square of the distance. Halley writes: distance. Halley writes:

Mr. Hook said he had had it, but that he Mr. Hook said he had had it, but that he would conceal it for some time so that others, would conceal it for some time so that others, triing and failing might know how to value it, triing and failing might know how to value it, when he should make it publick.when he should make it publick. (Yea, right!!! What a load!)(Yea, right!!! What a load!)

The Ideas of Isaac The Ideas of Isaac NewtonNewton

The central topic of the The central topic of the PrincipiaPrincipia was was gravitational force. Defined by Newton as:gravitational force. Defined by Newton as:

Fg = G (MFg = G (M11) (M) (M22)/ r)/ r2 2 where: (the inverse where: (the inverse square law)square law)

Fg = The force of gravityFg = The force of gravityG = The gravitational constantG = The gravitational constantM1 = The mass of body oneM1 = The mass of body oneM2 = The mass of body twoM2 = The mass of body twor = the distance between the centers of the two r = the distance between the centers of the two

bodiesbodies

Sir Isaac NewtonSir Isaac Newton Orbital flight was explained by Orbital flight was explained by

Newton in a though activity called Newton in a though activity called the “mountain cannon”.the “mountain cannon”.Is seeks to show how an object may Is seeks to show how an object may continually fall and still never his the continually fall and still never his the ground of a round body.ground of a round body.

http://galileoandeinstein.physics.virghttp://galileoandeinstein.physics.virginia.edu/more_stuff/Applets/newt/neinia.edu/more_stuff/Applets/newt/newtmtn.htmlwtmtn.html

Newton’s First Law of Newton’s First Law of MotionMotion

Newton’s First Law of Motion Newton’s First Law of Motion states that:states that:

F = ma F = ma where:where:

F = forceF = force

m = massm = mass

a = accelerationa = acceleration

Newton’s Second Law of Newton’s Second Law of MotionMotion

Newton’s Second Law of Motion is Newton’s Second Law of Motion is the Law of Inertia which states that:the Law of Inertia which states that:

A body in motion tends to stay in A body in motion tends to stay in motion (in a straight line) and a body motion (in a straight line) and a body at rest tends to stay at rest, unless at rest tends to stay at rest, unless acted upon by some external force.acted upon by some external force.Mass resists change and the Mass resists change and the natural state of matter is to be in natural state of matter is to be in motion!motion!

Newton’s Third Law of Newton’s Third Law of MotionMotion

Newton’s Third Law of Motion Newton’s Third Law of Motion states:states:

For every action there is an equal, For every action there is an equal, but opposite, reaction.but opposite, reaction.

Or, if I push you, then you push me Or, if I push you, then you push me andand

if you push me then I push you!if you push me then I push you!

Isaac NewtonIsaac Newton

Creator of:Creator of: Reflecting telescopeReflecting telescope Laws of MotionLaws of Motion Laws of GravityLaws of Gravity CalculusCalculus AstrophysicsAstrophysics Our understanding of the true nature Our understanding of the true nature

of lightof light(Not a bad resume, eh?)(Not a bad resume, eh?)

By Ken Journigan Independence High Astronomy The History of Astronomy The History of Astronomy.

Documents

Transcript of By Ken Journigan Independence High Astronomy The History of Astronomy The History of Astronomy.