astronomical terms rotation –motion around an axis –produces day/night from:...
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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
Ancient Greece
(600 BCE – 150 CE)
PSCI 131: Origins of Astronomy –Ancient Greece
Assumptions of the Ancient Greeks
• Universe– Earth– Seven “planetai”– Stars
• Geocentrism
• Celestial immutability
PSCI 131: Origins of Astronomy – Ancient Greece
From redorbit.com
Important Discoveries• Earth is spherical
– Aristotle
– Observation of lunar eclipses
– What evidence did he observe?
PSCI 131: Origins of Astronomy – Ancient Greece
From 8planets.co.uk
Important Discoveries• Earth is spherical
– What would Earth’s shadow look like if Earth were a flat disk?
PSCI 131: Origins of Astronomy – Ancient Greece
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Important Discoveries• Earth’s circumference
– Eratosthenes
– Measuring angle of shadows
– Basic geometry
PSCI 131: Origins of Astronomy – Ancient Greece
From 3villagecsd.k12.ny.us
Eratosthenes, 276-194 BCE
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)
PSCI 131: Origins of Astronomy – Ancient Greece
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Important Discoveries: Earth’s circumference
PSCI 131: Origins of Astronomy – Ancient Greece
• 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
• 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• Heliocentric (sun-centered) solar
system
– Aristarchus
– Sun much larger than Earth, further away than Moon
– Basic geometry
PSCI 131: Origins of Astronomy – Ancient Greece
From amazing-space.stsci.edu
Important Discoveries• Rejection of heliocentric model
– Predicted stellar parallax, but none was observed
• Need a telescope to see it
– Aristotle championed geocentric model
PSCI 131: Origins of Astronomy – Ancient Greece
Important Discoveries• Ptolemaic System
– Ptolemy
– Geocentric model
– First organized explanation of celestial motion
PSCI 131: Origins of Astronomy – Ancient Greece
Important Discoveries: Ptolemaic System
• Deferent: orbital path• Epicycles: smaller circles
– Used to explain retrograde motion
PSCI 131: Origins of Astronomy – Ancient Greece
Important Discoveries: Ptolemaic System
• Retrograde motion: “backward” motion of a planet along its orbital path
PSCI 131: Origins of Astronomy – Ancient Greece
The Ptolemaic System used epicycles to explain retrograde motion
Important Discoveries: Ptolemaic System
• Retrograde motion is really an illusion
PSCI 131: Origins of Astronomy – Ancient Greece
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
• 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
PSCI 131: Origins of Astronomy – European Renaissance
Timeline: Nicolaus Copernicus
1400 1776
1450First
printing press
1473 1543
Copernicus
1492
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
1400 1776
1450First
printing press
1473 1543
Copernicus
1492 1546 1601
Brahe
PSCI 131: Origins of Astronomy – European Renaissance
Tycho Brahe• Very precise astronomical
observations– Without a telescope
• Geocentrist– Apparent absence of stellar
parallax
PSCI 131: Origins of Astronomy – European Renaissance
Timeline: Johannes Kepler
1400 1776
1450First
printing press
1473 1543
Copernicus
1492 1546 1601
Brahe
1571 1630Kepler
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
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
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
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
PSCI 131: Origins of Astronomy – European Renaissance - Kepler
Second Law of Planetary Motion• Orbital speed varies inversely with orbital distance
From: http://www.wallpaperswala.com/solar-system/
Slower orbital speed
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
PSCI 131: Origins of Astronomy – European Renaissance - Kepler
Laws of Planetary Motion
• Significance
– First mathematical model of celestial motion
– Not based on philosophical assumptions
PSCI 131: Origins of Astronomy – European Renaissance
Timeline: Galileo Galilei
1400 1776
1450First
printing press
1473 1543
Copernicus
1492 1546 1601
Brahe
1571 1630Kepler
1564 1642Galileo
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
PSCI 131: Origins of Astronomy – European Renaissance - Galileo
• 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
From: en.wikipedia.org
Sizes of the Galilean moons shown relative to Jupiter
The Galilean Moons
PSCI 131: Origins of Astronomy – European Renaissance - Galileo
From: splung.com
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: physics.wisc.edu
The Galilean Moons
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
PSCI 131: Origins of Astronomy – European Renaissance - Galileo
Sunspots
From: galileo.rice.edu From: galileo.rice.edu
Series of Galileo’s 1612 sketches in a “flip-book” animation Sunspots through a modern telescope
• Refuted celestial immutability
PSCI 131: Origins of Astronomy – European Renaissance
Timeline: Isaac Newton
1400 1776
1450First
printing press
1473 1543
Copernicus
1492 1546 1601
Brahe
1571 1630Kepler
1564 1642Galileo
1727
Newton
1642
PSCI 131: Origins of Astronomy – European Renaissance
Sir Isaac Newton• Law of Universal Gravitation
• Law of Inertia
• Explained why planets move in orbits
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
PSCI 131: Origins of Astronomy – European Renaissance - Newton
Universal Gravitation
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
PSCI 131: Origins of Astronomy – European Renaissance - Newton
Gravity + Inertia = Orbit
An orbit is a balance between gravity and inertia
Earth Motions
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
PSCI 131: Origins of Astronomy –Earth Motions
Revolution: Perihelion & aphelionPSCI 131: Origins of Astronomy –Earth Motions
From: universetoday.com
Revolution: Solstices & equinoxesPSCI 131: Origins of Astronomy –Earth Motions
From: oceanservice.noaa.gov
Precession•Wobble of Earth on its axis; 26,000-yr cycle
PSCI 131: Origins of Astronomy –Earth Motions
The Earth-Moon System
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
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
PSCI 131: Origins of Astronomy – Earth-Moon System-Lunar Phases
End of Origins of Astronomy
PSCI 131: Origins of Astronomy