Pioneers in AstronomyPioneers in Astronomy

PtolemyPtolemy CopernicusCopernicus Tycho BraheTycho Brahe KeplerKepler GalileoGalileo NewtonNewton HalleyHalley Le Verrier & AdamsLe Verrier & Adams

Uraniborg, Tycho Brahe’s Observatory

PtolemyPtolemy

Almagest Almagest (150 AD), (150 AD), Ptolemy described Ptolemy described the Greek geocentric the Greek geocentric (earth-centered) (earth-centered) model of the universemodel of the universe

Order outward from Order outward from the earth based on the earth based on their apparent speeds their apparent speeds of motion of motion

Orbits were Orbits were considered circlesconsidered circles

Ptolemaic SystemPtolemaic System

http://www.thebigview.com/spacetime

Retrograde Mars, 1995Retrograde Mars, 1995

Retrograde Mars (2003)Retrograde Mars (2003)

http://zuserver2.star.ucl.ac.uk/~apod/apod/ap031216.html

Ptolemy’s EpicyclePtolemy’s Epicycle

Retrograde Planetary MotionRetrograde Planetary Motion

Animation 2.1: Retrograde MotionAnimation 2.1: Retrograde MotionAnimation 2.2: The Path of MarsAnimation 2.2: The Path of Mars

““It is most retrograde to our desire…”It is most retrograde to our desire…”

——HamletHamlet

Nicholas CopernicusNicholas Copernicus Copernicus (1473-1543)

developed heliocentric (sun-centered) model of the solar system

His book, De revolutionibus orbium coelestium (On the Revolutions of the Celestial Spheres, 1543), is considered the starting point of modern astronomy

Copernican SystemCopernican System

Copernican RevolutionCopernican Revolution

• In the Copernican solar system, the retrograde motion of Mars is seen when the Earth passes Mars in its orbit around the Sun

Retrograde Mars (June 2007)Retrograde Mars (June 2007)

Heliocentric ExplanationHeliocentric Explanation

Animation 2.3: A Heliocentric Explanation Animation 2.3: A Heliocentric Explanation of Retrograde Motionof Retrograde Motion

Tycho BraheTycho Brahe

Tycho Brahe (1546-Tycho Brahe (1546-1601) recorded 1601) recorded precise observations precise observations of the positions of the of the positions of the planets and starsplanets and stars

Tycho’s data was Tycho’s data was used by Kepler to used by Kepler to formulate the laws of formulate the laws of planetary motionplanetary motion

Tycho’s SystemTycho’s System

Tycho created a compromise between the universes of Ptolemy and Copernicus

Planets orbit sun, sun orbits earth

http://media4.obspm.fr/public/IUFM/images/13Kepler/images/ticho_brahe.png

Johannes KeplerJohannes Kepler

• Using Tycho’s observations, Johannes Kepler (1571-1630) deduced three laws of planetary motion

Kepler’s First LawKepler’s First Law

K1: The orbit of a K1: The orbit of a planet around the Sun planet around the Sun is an ellipse with the is an ellipse with the Sun at one focusSun at one focus

Elliptical OrbitsElliptical Orbits

Close and FarClose and Far

• Perihelion:Perihelion: The point in a planet’s orbit The point in a planet’s orbit closest to the Sunclosest to the Sun

• Aphelion:Aphelion: Point farthest from sun Point farthest from sun

Earth, 2007Earth, 2007

Perihelion: Jan 03Perihelion: Jan 03

Aphelion: July 07Aphelion: July 07

Kepler’s Second LawKepler’s Second Law

K2: A line joining the planet and the Sun K2: A line joining the planet and the Sun sweeps out equal areas in equal intervals sweeps out equal areas in equal intervals of timeof time

Planets speed up as they approach the Planets speed up as they approach the sun, slow down when the move away from sun, slow down when the move away from the sunthe sun

K1, K2 published in 1609, K1, K2 published in 1609, Astronomia Astronomia NovaNova

Planet moves Planet moves faster in its orbit faster in its orbit when closer to the when closer to the Sun.Sun.

Planet moves Planet moves slower in its orbit slower in its orbit when farther away when farther away from the Sun.from the Sun.

Equal AreasEqual Areas

Kepler’s First & Second LawsKepler’s First & Second Laws

Animation 2.4: Kepler’s First and Second Animation 2.4: Kepler’s First and Second LawsLaws

Kepler’s Third Law (Harmonic, Kepler’s Third Law (Harmonic, 1619)1619)

K3: The square of a planet’s sidereal K3: The square of a planet’s sidereal period (P) around the Sun is directly period (P) around the Sun is directly proportional to the cube of its semi-major proportional to the cube of its semi-major axis (a)axis (a)

P2 = a3

The results are in astronomical units (AU) The results are in astronomical units (AU) with earth = 1with earth = 1

1 AU = 93,000,000 miles1 AU = 93,000,000 milesDemo: ClickDemo: Click

GalileoGalileo

• Galileo (1564-1642), first scientist to use a telescope to examine the night sky

• Discoveries supported the Copernican system

Phases of VenusPhases of Venus

Moons of Jupiter (Galileo, 1610)Moons of Jupiter (Galileo, 1610)

Isaac NewtonIsaac Newton

Isaac Newton (1643-Isaac Newton (1643-1727) 1727)

Laws of motionLaws of motion Law of gravityLaw of gravity Invented calculusInvented calculus Newton’s laws were first Newton’s laws were first

published in the published in the Philosophiae Naturalis Philosophiae Naturalis Principia MathematicaPrincipia Mathematica, or , or PrincipiaPrincipia, 1687, 1687

Newton’s First LawNewton’s First Law

N1: A body remains at rest or moves in a N1: A body remains at rest or moves in a straight line at constant speed unless straight line at constant speed unless acted upon by a net outside forceacted upon by a net outside force

Spaceship moving in spaceSpaceship moving in space

Newton’s Second LawNewton’s Second Law

N2: The acceleration (a) of an object is N2: The acceleration (a) of an object is proportional to the force (F) acting on itproportional to the force (F) acting on it

F = maF = mam = mass of objectm = mass of objectSpin ball on a stringSpin ball on a string

Newton’s Third LawNewton’s Third Law

Whenever one body exerts a force on a Whenever one body exerts a force on a second body, the second body exerts an second body, the second body exerts an equal and opposite force on the first bodyequal and opposite force on the first body

Or, every action has an equal and Or, every action has an equal and opposite reactionopposite reaction

Rocket liftoffRocket liftoff

Law of GravityLaw of Gravity

Law of Universal GravitationLaw of Universal GravitationTwo objects attract each other with a force

that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them.

Newtonian OrbitsNewtonian Orbits

Conic SectionsConic Sections

Slice a cone at Slice a cone at various anglesvarious angles

Resulting shapes Resulting shapes same as planetary same as planetary orbitsorbits

Practical math, Practical math, Greece, 200 BCGreece, 200 BC

Comet & Planetary OrbitsComet & Planetary Orbits

Animation 2.5: Planetary OrbitsAnimation 2.5: Planetary OrbitsAnimation 2.6: Orbit & Tail of a CometAnimation 2.6: Orbit & Tail of a Comet

Newton’s CannonNewton’s Cannon

““Cannon” OrbitsCannon” Orbits

Edmond HalleyEdmond Halley Edmond Halley (1656-Edmond Halley (1656-

1742) used Newton’s 1742) used Newton’s methods to describe a methods to describe a comet’s orbit and predict comet’s orbit and predict its returnits return

Halley explained comet Halley explained comet sightings of 1456, 1531, sightings of 1456, 1531, 1607, and 1682 to be the 1607, and 1682 to be the same cometsame comet

Predicted return in 1758 Predicted return in 1758 Comet Halley was last Comet Halley was last

visible in 1986 and will visible in 1986 and will return in 2061return in 2061

Comet HalleyComet Halley

Portion of Bayeux Tapestry, 1066 Comet Halley in 1986,

Milky Way in upper right

Le Verrier and AdamsLe Verrier and Adams English astronomer John

Couch Adams (1819-1892) and French astronomer Urbain Jean Joseph Le Verrier (1811-1877) independently predicted the existence of Neptune

Predictions based upon Neptune’s gravitational effect upon Uranus

Neptune was discovered at the Berlin Observatory on Sept 23, 1846

Le Verrier (left) & Adams

Neptune’s PositionsNeptune’s Positions

1-degree equals the width of an oustretched fingertip

Inferior & SuperiorInferior & Superior

Planet positions compared to earthPlanet positions compared to earth Inferior PlanetsInferior Planets: Between sun and earth: Between sun and earth

Mercury, VenusMercury, VenusSuperior PlanetsSuperior Planets: Farther from the sun : Farther from the sun

than earththan earthMars, Jupiter, Saturn, Uranus, Neptune, Mars, Jupiter, Saturn, Uranus, Neptune,

(Pluto)(Pluto)

Inferior PlanetsInferior Planets

Eastern and western Eastern and western elongationelongation

Inferior conjunction Inferior conjunction Superior conjunctionSuperior conjunction

Superior PlanetsSuperior Planets

Opposition Opposition ConjunctionConjunction

Close & FarClose & Far

SummarySummary