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ASTB03H3 Study Guide - Final Guide: Spectroscopy, Deferent And Epicycle, Almagest


Department
Astronomy
Course Code
ASTB03H3
Professor
Dan Silver
Study Guide
Final

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ASTB03 Study Notes
Celestial Sphere:
- sky appears as shell
- stars attached, carried as shell rotates
- provides background for observations
Suns Motion (ancient)
- Sun and Celestial Sphere move from east to west around Earth
- Sun not attached to CS
- Sun is slower then CS by 1 degree/day
- 365 ¼ days for sun to return to same position
- Sun appears to revolve in 24hrs…. CS rotates in 23hr 56min
Moons Motion
- moon moves 13 degrees per day relative to CS (eastward)
- 27.3 days for complete cycle
- moon phase : 29.5 day cycle (lunar month)
Planets
- 5 objects visible to naked eye (mercury, venus, mars, Jupiter, Saturn)
- usually move steadily eastward relative to CS
- retrograde motion
Role of Astronomy
Timekeeping :
Calendars- Egypt—3000 BC, China—14th century BC, Americas--500AD
Spiritual/religious events
Recurring seasonal phenomena
Astronomers= priests
Greek Astronomy:
Beginning f Scientific approach (600BC-200AD)
Geometry
- nature described by perfect geometric objects (plato)
- straight lines, circles, spheres, uniform motion
- Eudoxus (409BC) – planets attached to rotating geocentric spheres – spheres
mathematical abstraction
Aristotle (384 BC)
Spherical Earth:
- new stars appear when traveling north or south
- curved shadow of earth during lunar eclipses
- elephants in Morocco and India
Stationary Earth:
-objects would be left behind by rotating or revolving Earth (basic Aristotelian physics)

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- moving earth would produce parallax shift in stars positions
Astronomical Measurements
Aristarchus (310BC):
-relative distances or moon and sun
- based on observations of timing moons phase
found- sun 19x further then moon (correct 392x)
found sun 7x diameter of earth (correct 109x)
Eratosthenes (276 BC)
- finds absolute size of earth
- observations of positions of sun from 2 locations ( Alexandria and Syene)
- shadows indicated 7 degrees between cities
- circumference is 360/7 x distance between cities
- known distance means circumference of earth is 250,000 stade (40,000 kms)
Motion in Greek Models
Apollonius (220 BC)
- introduced eccentric circles, deferents and epicycles
- planets paths not circular
- epicycle’s needed to explain retrograde motion
Hipparchus (190BC)
- catalogue of star positions
- distance of moon 64 x radius of Earth
- modified Apollonius eccentric model
Magnitude Scale for Brightness
- visible stars ranked into 6 brightness categories: magnitudes
- brightest: 1st magnitude , dimmest: 6th magnitude
- observed brightness = apparent magnitude (m)
- higher apparent magnitude = dimmer.. magnitude can be negative for bright
objects
- Sun: m= -26.8 , Moon: m= -12.5 , light bulb: m= -19, Venus: m= -4.4
Ptolemy
Almagest (140 AD)
- star catalogue
- circumference of earth = 180,000 stade
Geocentric Model of Universe
- spherical, stationary earth at center
- rotating celestial sphere
- deferent + epicycle orbits
- survived for 1500 years
Transition to Renaissance
- Almagest passes to Roman, Byzantine, Islamic empires
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