Transcript History of Astronomy

History of Astronomy
Motions of the sky
caused by and
controlled by gods.
Big Horn Medicine
Temple at Caracol
Greek Astronomy - 600 BC
 Science - “to learn”
 Thales - the world is
logical/understandable.
 Stars are “balls of fire.”
 Predicted solar eclipse.
Pythagoreans
Math is the
language of music;
language of science
Perfect triangle divine number.
Pythagorean
Theorem
Round earth &
moon
Classical Greece - 450-300 BC
 Socrates (470-399 BC)
 Plato (430-350 BC)
 Aristotle (384-322 BC)
 Alexander the Great
 Democritus
Aristotl
e
Helenistic Era:350 BC - 400 AD
Alexandria intellectual hub of
the world.
Aristarchus
 (310-230 BC) earth orbits the sun
Erastosthenes
 Circumference of Earth
(276-200 BC)
Ptolemy - Geocentric Universe
 127-145 AD
 Deferents & Epicycles
 Retrograde Motion
 Almagest - “Greatest of
All Books”
Geocentric Universe
 Earth at center
 Spheres for each planet
(Mercury, Venus, Mars,
Jupiter & Saturn); Moon,
Sun, Zodiac constellations,
stars.
Retrograde Motion
Hipparchus (190-120 BC)
Catalog stars
Calculate lunar
month
Precession of
equinoxes
Europe - The Dark Ages
• Calendars didn’t work!
• Mercury and Venus were different.
• Occam’s Razor
The Copernican Revolution
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Nicolas Copernicus
1473 - 1543; Poland
Canon in church; Calendar reform
Heliocentric model
“On Revolutions”
Explanations of Retrograde Motion
Ptolemaic
Epicycles & Deferents
Copernican
Inner Planets move faster
Tycho Brahe (1546 - 1601)
 Great naked-eye observer
 Supernova of 1572
 Comet - outside of atmosphere
 Uraniborg observatory
 Prague & Kepler
My Tycho
Johannes Kepler (1571 - 1630)
 Tycho’s assistant - 1600
 Determine the orbit of Mars
 Astrology
 Three Laws of Planetary Motion
1st Law of Planetary Motion
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The orbits of planets are ellipses with the sun at one focus.
1.
Semi-major axis - Astronomical Unit
2.
Eccentricity; e = c/a
2nd Law of Planetary Motion
 Planets travel faster at perihelion, slower at aphelion;
but sweep out equal areas of space in equal amounts
of time.
3rd Law of Planetary Motion
 The square of a planet’s orbital period is proportional to its
semi-major axis cubed.
k = P2/R3
 Period is in Earth years
 Radius is in AU
 k=1
P2 = R 3
Galileo Galilei (1564 - 1642)
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1609 - Telescope
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Venus
Sun
Moon
Jupiter
Saturn
1610 - Published
1632 “Dialogue Concerning
the Two Chief World
Systems”
House Arrest
Telescope; diagrams of planets
Sunspots; Jupiter’s Moons
Isaac Newton (1642 - 1727)
 Born Christmas Day
 Cambridge; closed for
plague
 Age 23-24; 18 mos. invented
calculus
 Optics
 Laws of Motion, Law of
Universal Gravitation
 Explained Kepler’s Laws
 “Principia”
Newton’s Laws of Motion
First Law: Every body continues in a state
of rest or in a state of motion in a straight
line unless it is compelled to change that
state by a force acting on it.
Second Law: When a force F acts on a
body of mass m, it produces and
acceleration a equal to the force divided by
the mass.Thus, a=F/m, or F=ma.
Third Law; To every action there is an
equal and opposite reaction.
Gravitation
Every particle of matter in the universe attracts every other
particle with a force that is directly proportional to the product
of the masses of the particles and inversely proportional to the
square of the distance between them.