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Origins of Modern Astronomy
PSCI 131
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Astronomical Terms Rotation Motion around an axis Produces day/night
From: physicalgeography.net
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Astronomical Terms Revolution Motion around another object; orbiting
Produces seasons From: science-class.net
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Astronomical Terms Orbital period Time required for one revolution
Length of one year for a given planet school-for-champions.com
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Astronomical Terms Orbital distance Average distance from the Sun
Solar system shown to size and distance scale From: commons.wikimedia.org
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Astronomical Terms Astronomical unit (AU) Distance from Earth to Sun
Used as a “measuring stick” for solar system distances From: wchs-astronomy.wikispaces.com
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Astronomical Terms Parallax
Apparent shift of objects due to motion of observer Stellar parallax: apparent shift of stars due to Earth’s movement around Sun
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Astronomical Terms Geocentric: Earth-centered
Heliocentric: Sun-centered
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ORIGINS OF ASTRONOMY Ancient Greece (600 BCE – 150 CE)
European Renaissance (1400s-1700s) Earth Motions Earth-Moon System
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Ancient Greece (600 BCE – 150 CE)
PSCI 131: Origins of Astronomy –Ancient Greece Ancient Greece (600 BCE – 150 CE)
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Assumptions of the Ancient Greeks
PSCI 131: Origins of Astronomy – Ancient Greece Assumptions of the Ancient Greeks Universe Earth Seven “planetai” Stars Geocentrism Celestial immutability From redorbit.com
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Important Discoveries
PSCI 131: Origins of Astronomy – Ancient Greece Important Discoveries Earth is spherical Aristotle Observation of lunar eclipses What evidence did he observe? From 8planets.co.uk
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Important Discoveries
PSCI 131: Origins of Astronomy – Ancient Greece Important Discoveries Earth is spherical What would Earth’s shadow look like if Earth were a flat disk? ? ? ?
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Important Discoveries
PSCI 131: Origins of Astronomy – Ancient Greece Important Discoveries Earth’s circumference Eratosthenes Measuring angle of shadows Basic geometry Eratosthenes, BCE From 3villagecsd.k12.ny.us
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Important Discoveries: Earth’s circumference
PSCI 131: Origins of Astronomy – Ancient Greece Important Discoveries: Earth’s circumference Two ways to measure circumference Degrees and length (stadion: ancient unit of length) Earth’s circumf. = 360 degrees = ____ stadia Need distance between two points in degrees and stadia Distance from Syene to Alexandria was known to be 5000 stadia (about 480 miles) ?
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Important Discoveries: Earth’s circumference
PSCI 131: Origins of Astronomy – Ancient Greece Important Discoveries: Earth’s circumference How did Eratosthenes find distance in degrees? Angle of shadows in both cities on same day At Syene: no shadow At Alexandria: shadow made 7 degree angle
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Important Discoveries: Earth’s circumference
PSCI 131: Origins of Astronomy – Ancient Greece Important Discoveries: Earth’s circumference Since 360°÷ 7°= about 50, Earth’s circumference must be about 50 times the Syene-Alexandria distance 5000 stadia x 50 = 250,000 stadia or 24,500 miles (actual: 24,901 mi)
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Important Discoveries
PSCI 131: Origins of Astronomy – Ancient Greece Important Discoveries Heliocentric (sun-centered) solar system Aristarchus Sun much larger than Earth, further away than Moon Basic geometry From amazing-space.stsci.edu
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Important Discoveries
PSCI 131: Origins of Astronomy – Ancient Greece Important Discoveries Rejection of heliocentric model Predicted stellar parallax, but none was observed Need a telescope to see it Aristotle championed geocentric model
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Important Discoveries
PSCI 131: Origins of Astronomy – Ancient Greece Important Discoveries Ptolemaic System Claudius Ptolemy Geocentric model First organized explanation of celestial motion
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Important Discoveries: Ptolemaic System
PSCI 131: Origins of Astronomy – Ancient Greece Important Discoveries: Ptolemaic System Deferent: orbital path Epicycles: smaller circles Used to explain retrograde motion
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Important Discoveries: Ptolemaic System
PSCI 131: Origins of Astronomy – Ancient Greece Important Discoveries: Ptolemaic System Retrograde motion: “backward” motion of a planet along its orbital path The Ptolemaic System used epicycles to explain retrograde motion
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Important Discoveries: Ptolemaic System
PSCI 131: Origins of Astronomy – Ancient Greece Important Discoveries: Ptolemaic System Retrograde motion is really an illusion Earth passes Mars in its orbit; Mars appears to move backward as seen from Earth
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European Renaissance (1400s – 1700s)
PSCI 131: Origins of Astronomy –European Renaissance European Renaissance (1400s – 1700s)
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Timeline: Nicolaus Copernicus
PSCI 131: Origins of Astronomy – European Renaissance Timeline: Nicolaus Copernicus Copernicus 1473 1543 1400 1776 1492 1450 First printing press
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Nicolaus Copernicus “Copernican Revolution” Heliocentrism
PSCI 131: Origins of Astronomy – European Renaissance Nicolaus Copernicus “Copernican Revolution” Heliocentrism Set stage for later discoveries
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PSCI 131: Origins of Astronomy – European Renaissance
Timeline: Tycho Brahe Copernicus 1473 1543 1400 1776 1492 1450 1546 1601 First printing press Brahe
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Tycho Brahe Very precise astronomical observations Geocentrist
PSCI 131: Origins of Astronomy – European Renaissance Tycho Brahe Very precise astronomical observations Without a telescope Geocentrist Apparent absence of stellar parallax
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Timeline: Johannes Kepler
PSCI 131: Origins of Astronomy – European Renaissance Timeline: Johannes Kepler Copernicus Kepler 1473 1543 1571 1630 1400 1776 1492 1450 1546 1601 First printing press Brahe
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Johannes Kepler Brahe’s assistant Used Brahe’s observations
PSCI 131: Origins of Astronomy – European Renaissance Johannes Kepler Brahe’s assistant Used Brahe’s observations To prove heliocentrism To develop laws of planetary motion still in use today
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First Law of Planetary Motion
PSCI 131: Origins of Astronomy – European Renaissance - Kepler First Law of Planetary Motion Orbits are ellipses, not circles Sun located at one focus of the ellipse The pushpins are at the foci of the ellipse
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First Law of Planetary Motion
PSCI 131: Origins of Astronomy – European Renaissance - Kepler First Law of Planetary Motion Orbits are ellipses, not circles Sun located at one focus of the ellipse From: csep10.phys.utk.edu
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Second Law of Planetary Motion
PSCI 131: Origins of Astronomy – European Renaissance - Kepler Second Law of Planetary Motion Law of equal areas During a given amount of time, a planet will always “sweep out” the same area in its orbit over that time From: dallaskasaboski.blogspot.com
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Second Law of Planetary Motion
PSCI 131: Origins of Astronomy – European Renaissance - Kepler Second Law of Planetary Motion Orbital speed varies inversely with orbital distance Slower orbital speed From:
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Third Law of Planetary Motion
PSCI 131: Origins of Astronomy – European Renaissance - Kepler Third Law of Planetary Motion Orbital period proportional to orbital distance p2 = d3 p: orbital period in Earth years d: orbital distance in astronomical units (AUs) Example: if p = 8 yrs, d = 4 AUs
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Laws of Planetary Motion
PSCI 131: Origins of Astronomy – European Renaissance - Kepler Laws of Planetary Motion Significance First mathematical model of celestial motion Not based on philosophical assumptions
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Timeline: Galileo Galilei
PSCI 131: Origins of Astronomy – European Renaissance Timeline: Galileo Galilei Kepler 1571 1630 Copernicus 1564 Galileo 1642 1473 1543 1400 1776 1492 1450 1546 1601 First printing press Brahe
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Galileo Galilei “Father of modern observational science”
PSCI 131: Origins of Astronomy – European Renaissance Galileo Galilei “Father of modern observational science” Improvements to telescopes Did not invent them First astronomer to use telescope
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The Galilean Moons Discovered four of Jupiter’s moons
PSCI 131: Origins of Astronomy – European Renaissance - Galileo The Galilean Moons Discovered four of Jupiter’s moons Io, Ganymede, Callisto, Europa First observation of moons other than Earth’s Showed that Earth isn’t unique in having a natural satellite Sizes of the Galilean moons shown relative to Jupiter From: en.wikipedia.org
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PSCI 131: Origins of Astronomy – European Renaissance - Galileo
The Galilean Moons Galileo’s notebook showing changing positions of Galilean moons over two weeks Jupiter and the Galilean moons through a small telescope, as Galileo saw them From: splung.com From: physics.wisc.edu
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PSCI 131: Origins of Astronomy – European Renaissance - Galileo
The Phases of Venus Observed that Venus goes through phases like Earth’s moon Proof of heliocentrism From: oneminuteastronomer.com
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Sunspots Refuted celestial immutability
PSCI 131: Origins of Astronomy – European Renaissance - Galileo Sunspots Refuted celestial immutability Series of Galileo’s 1612 sketches Sunspots through a modern telescope 2 hours of sunspot motion
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Timeline: Isaac Newton
PSCI 131: Origins of Astronomy – European Renaissance Timeline: Isaac Newton Kepler 1571 1630 Copernicus 1564 Galileo 1642 1473 1543 1400 1776 1492 1450 1546 1601 1642 1727 First printing press Newton Brahe
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Sir Isaac Newton Law of Universal Gravitation Law of Inertia
PSCI 131: Origins of Astronomy – European Renaissance Sir Isaac Newton Law of Universal Gravitation Law of Inertia Explained why planets move in orbits
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Universal Gravitation
PSCI 131: Origins of Astronomy – European Renaissance - Newton Universal Gravitation All objects in the universe exert an attractional force on each other Force increases with mass and decreases with distance
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Law of Inertia (Newton’s First Law)
PSCI 131: Origins of Astronomy – European Renaissance - Newton Law of Inertia (Newton’s First Law) An object in motion continues in motion with the same speed and in the same direction unless acted upon by an external force From: drcruzan.com
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Gravity + Inertia = Orbit
PSCI 131: Origins of Astronomy – European Renaissance - Newton Gravity + Inertia = Orbit An orbit is a balance between gravity and inertia
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PSCI 131: Origins of Astronomy –Earth Motions
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Revolution Period of revolution: 365.25 days
PSCI 131: Origins of Astronomy –Earth Motions Revolution Period of revolution: days Leap year Perihelion: closest to Sun (January) Aphelion: furthest from Sun (July) Solstices & Equinoxes
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Revolution: Perihelion & aphelion
PSCI 131: Origins of Astronomy –Earth Motions Revolution: Perihelion & aphelion From: universetoday.com
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Revolution: Solstices & equinoxes
PSCI 131: Origins of Astronomy –Earth Motions Revolution: Solstices & equinoxes From: oceanservice.noaa.gov
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Precession Wobble of Earth on its axis; 26,000-yr cycle
PSCI 131: Origins of Astronomy –Earth Motions Precession Wobble of Earth on its axis; 26,000-yr cycle
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PSCI 131: Origins of Astronomy –Earth-Moon System
The Earth-Moon System
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The Earth-Moon System Mean Earth-Moon distance: ~238,000 mi
PSCI 131: Origins of Astronomy –Earth-Moon System The Earth-Moon System Mean Earth-Moon distance: ~238,000 mi Period of rotation: 27.5 days Period of revolution: 27.5 days “Synchronous” orbit Same side always faces Earth
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Lunar Phases Half of lunar surface always lit
PSCI 131: Origins of Astronomy –Earth-Moon System Lunar Phases Half of lunar surface always lit Exception: lunar eclipse Current phase depends on how much of lit surface is visible from Earth
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PSCI 131: Origins of Astronomy – Earth-Moon System-Lunar Phases
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Eclipses Solar Only occurs during a new moon
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Eclipses Lunar Only occurs during a full moon
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Eclipses Why don’t we have eclipses every new and full moon?
Moon’s orbit is tilted with respect to the ecliptic
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End of Origins of Astronomy
PSCI 131: Origins of Astronomy End of Origins of Astronomy
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