Unit1: The Physics of Astronomy - Mount Holyoke College...Unit1: The Physics of Astronomy This Week...
Transcript of Unit1: The Physics of Astronomy - Mount Holyoke College...Unit1: The Physics of Astronomy This Week...
Unit1: The Physics of Astronomy
This Week & Next: Astronomy in Motion
•Kepler’s Laws•Newton’s Laws•Work & Energy
General Note: Please ASK if there are terms/math/physics that are new to you!
Today: Historical Background & Basic Refresher
Why is Astronomy Different?
Astronomy is the Science of Observation rather than Experiment
X
What are the Most Basic Observable Quantities?
Light
Motion
What were the first objects routinely observed?
When?
A Little History...Astronomy is an ancient science
•Maya•Aztec•Egyptians•Chinese•Greek
II. Early Scientific Astronomy
Plato (350 BC):Geocentric Model of SS
-planets & Sun all orbit a stationary Earth - orbits are perfect spheres
vs.
Aristarchus (270 BC):First Heliocentric Model -planets orbit the Sun
-spherical orbits
REJECTED!X
Ptolemy (100 AD): added epicycles to better fit observed motion of planets
Almagest“The Great Treatise”
II. Early Scientific Astronomy
Medieval Manuscript, Melk Abbey (Austria):Geocentric Solar System!(pic fr. 4/17/09)
15th Century!
15th Century!
BUT–Predicted
locations of planets, by late 1400s PROVED WRONG
Medieval Manuscript, Melk Abbey (Austria):Geocentric Solar System!(pic fr. 4/17/09)
Copernicus (1473 - 1543): On the Revolution of Heavenly SpheresNew Heliocentric Model
BUT...
-still Spherical-contained epicycles
III. Groundbreakers
Tycho Brahe (1546-1601):
Best set of astronomical positions to date
III. Groundbreakers
I sez Copernicus not gud yet - no cheezburgers
– * Incredible observer– naked-eye observations– Planetary & stellar positions
good to <1’– Duel: who is a better
mathematician????
Johannes Kepler (1571-1630)
• Recognized need for model to match Tycho’s observations
•New laws of Planetary Motion (1609)
What are Kepler’s 3 Laws of Planetary Motion?
III. Groundbreakers
Kepler’s Laws of Planetary MotionK1: Planets orbit the Sun in an ellipse, with the Sun at one focus of the ellipse
K2: A line connecting a planet to the Sun sweeps out equal areas in equal time intervals
K3 (Harmonic Law): P2∝a3
The squares of the sidereal periods is proportional to the orbital semi-major axis cubed
Isaac Newton (1642-1747)Principia (1687)
Galileo (1564-1642)
The Physics of Motion!
Newton’s Laws of Motion
N1(Law of Inertia): An object at rest will remain at rest and an object in motion will remain in motion in a straight line at constant speed unless acted upon by an outside force
N2: The net force on an object is proportional to the object’s mass & acceleration
N3: For every action there is an equal and opposite reaction
Newton
What is the physical explanation for Kepler’s Laws of planetary motion??
Derivation of Universal Law of Gravity
What is the Nature of this Force???