Astronomical Terms Rotation Motion around an axis Produces day/night From: physicalgeography.net

Astronomical Terms Revolution Motion around another object; orbiting Produces seasons From: science-class.net

Astronomical Terms Orbital period Time required for one revolution Length of one year for a given planet school-for-champions.com

Astronomical Terms Orbital distance Average distance from the Sun Solar system shown to size and distance scale From: commons.wikimedia.org

Astronomical Terms Astronomical unit (AU) Distance from Earth to Sun Used as a “measuring stick” for solar system distances From: wchs-astronomy.wikispaces.com

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

Astronomical Terms Geocentric: Earth-centered Heliocentric: Sun-centered

ORIGINS OF ASTRONOMY Ancient Greece (600 BCE – 150 CE) Islamic Golden Age (700s-1400s) European Renaissance (1400s-1700s) Earth Motions Earth-Moon System

The Sun revolves around the Earth… …and so do the other planets and the stars

Geocentrism: Evidence We don’t feel the Earth moving, or fly off of it The Earth is far too massive to be able to move Stars don’t shift position over the course of each year (stellar parallax)

Ancient Greece (600 BCE – 150 CE) PSCI 131: Origins of Astronomy –Ancient Greece Ancient Greece (600 BCE – 150 CE)

Ancient Greek Astronomy PSCI 131: Origins of Astronomy –Ancient Greece Ancient Greek Astronomy The ancient Greeks knew the Earth is spherical TRUE or FALSE?

Ancient Greek Astronomy PSCI 131: Origins of Astronomy –Ancient Greece Ancient Greek Astronomy The ancient Greeks knew the Earth is spherical TRUE

Ancient Greek Astronomy PSCI 131: Origins of Astronomy –Ancient Greece Ancient Greek Astronomy The ancient Greeks knew the Earth’s true circumference (distance around the equator). TRUE or FALSE?

Ancient Greek Astronomy PSCI 131: Origins of Astronomy –Ancient Greece Ancient Greek Astronomy The ancient Greeks knew the Earth’s true circumference (distance around the equator). TRUE

Ancient Greek Astronomy PSCI 131: Origins of Astronomy –Ancient Greece Ancient Greek Astronomy The ancient Greeks knew about Saturn’s rings. TRUE or FALSE?

Ancient Greek Astronomy PSCI 131: Origins of Astronomy –Ancient Greece Ancient Greek Astronomy The ancient Greeks knew about Saturn’s rings. FALSE (can’t be seen without a telescope)

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

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

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? ? ? ?

Important Discoveries PSCI 131: Origins of Astronomy – Ancient Greece Important Discoveries Earth’s circumference Eratosthenes Measuring angle of shadows Basic geometry Eratosthenes, 276-194 BCE From 3villagecsd.k12.ny.us

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 in stadia was known to be 5000 stadia (about 480 miles) ?

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

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)

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

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

Important Discoveries PSCI 131: Origins of Astronomy – Ancient Greece Important Discoveries Ptolemaic System Ptolemy Geocentric model First organized explanation of celestial motion

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

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

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

Islamic Golden Age (700s – 1400s) PSCI 131: Origins of Astronomy Islamic Golden Age (700s – 1400s) Preserved and expanded work of ancient Greeks and Indians Detailed star catalogs, many observatories Most star names are Arabic Altair, Deneb, Aldebaran, etc.

European Renaissance (1400s – 1700s) PSCI 131: Origins of Astronomy –European Renaissance European Renaissance (1400s – 1700s)

Timeline: Nicolaus Copernicus PSCI 131: Origins of Astronomy – European Renaissance Timeline: Nicolaus Copernicus Copernicus 1473 1543 1400 1776 1492 1450 First printing press

Nicolaus Copernicus “Copernican Revolution” Heliocentrism PSCI 131: Origins of Astronomy – European Renaissance Nicolaus Copernicus “Copernican Revolution” Heliocentrism Set stage for later discoveries

PSCI 131: Origins of Astronomy – European Renaissance Timeline: Tycho Brahe Copernicus 1473 1543 1400 1776 1492 1450 1546 1601 First printing press Brahe

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

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

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

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

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

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 http://www.youtube.com/watch?v=_3OOK8a4l8Y From: dallaskasaboski.blogspot.com

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: http://www.wallpaperswala.com/solar-system/

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

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

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

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

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

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

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 http://astro.unl.edu/classaction/animations/renaissance/venusphases.html

Sunspots Refuted celestial immutability PSCI 131: Origins of Astronomy – European Renaissance - Galileo Sunspots Refuted celestial immutability Series of Galileo’s 1612 sketches in a “flip-book” animation Sunspots through a modern telescope From: galileo.rice.edu From: galileo.rice.edu

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

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

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

Universal Gravitation PSCI 131: Origins of Astronomy – European Renaissance - Newton Universal Gravitation

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

Gravity + Inertia = Orbit PSCI 131: Origins of Astronomy – European Renaissance - Newton Gravity + Inertia = Orbit An orbit is a balance between gravity and inertia

PSCI 131: Origins of Astronomy –Earth Motions

Rotation Solar day Sidereal day PSCI 131: Origins of Astronomy –Earth Motions Rotation Solar day Time from noon on one day to noon the next day: 24 hours Sidereal day Time required for a star to return to the same position on two successive nights: 23 hrs 56 minutes

Revolution Period of revolution: 365.25 days PSCI 131: Origins of Astronomy –Earth Motions Revolution Period of revolution: 365.25 days Leap year Perihelion: closest to Sun (January) Aphelion: furthest from Sun (July) Solstices & Equinoxes

Revolution: Perihelion & aphelion PSCI 131: Origins of Astronomy –Earth Motions Revolution: Perihelion & aphelion From: universetoday.com

Revolution: Solstices & equinoxes PSCI 131: Origins of Astronomy –Earth Motions Revolution: Solstices & equinoxes From: oceanservice.noaa.gov

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

PSCI 131: Origins of Astronomy –Earth-Moon System The Earth-Moon System

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

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

PSCI 131: Origins of Astronomy – Earth-Moon System-Lunar Phases

End of Origins of Astronomy PSCI 131: Origins of Astronomy End of Origins of Astronomy