Ch. 22 Origin of Modern Astronomy Sec. 1 Early Astronomy 200

Which model of the universe had Earth at the center? –geocentric believed everything orbited Earth –stars on transparent “celestial sphere” around Earth Early Astronomy sec. 1

What did early astronomers notice? –same constellations visible same time every year –some points of light “wander”  planets mostly W  E sometimes W  E, then E  W, & back to W  E –“retrograde motion”“retrograde motion” –ex. Mars The Movements of Planets & Stars

Retrograde Motion

Ptolemy’s Geocentric Model What was Ptolemy’s contribution to the geocentric model? –developed system to predict where planets would appear needed to account for retrograde motion –imagined planets on small circular orbits »“epicycles”

Which model of the universe did Copernicus propose that had the Sun at the center?Which model of the universe did Copernicus propose that had the Sun at the center? –heliocentric suggested  –Earth = planet  rotates on axis & revolves around Sun –retrograde motion because planets different distances & speeds Copernicus’s Model

What did Tycho Brahe contribute to early astronomy? –most precise records before invention of telescope died before applying his data –His assistant, Johannes Kepler, built on his work. Tycho, Kepler, & Planetary MotionKepler

What did Kepler contribute to astronomy? –Laws of planetary motion (that elliptical orbits could explain unexpected occurences) First Law of Planetary Motion –planets  elliptical orbits w/ one focus Second Law of Planetary Motion –Equal Area Law Third Law of Planetary Motion –Harmonic Law »Period 2 = Distance 3 »Why do farther planets have longer periods? ~b/c orbit is larger & it moves slower than planets closer to the sun Tycho, Kepler, & Planetary MotionKepler

Planets’ orbits are elliptical w/ one focus –eccentricity (e) is measure of how flattened ellipse is e = d L= length of major axis F1F1 F2F2 d= the distance between the foci L 1st Law of Planetary Motion: Law of Orbits

Eccentricity ranges from 0 to 1 –eccentricity of circle = ? 0 –Why? »foci on top of each other (distance = 0) –Eccentricity of line = ? 1 –Why? »distance between foci = length of major axis L 1st Law of Planetary Motion: Law of Orbits Most planetary orbits are NEARLY circular… eccentricity close to 0!

A line connecting Earth to the Sun will pass over equal areas in equal time –“triangle” (area)  short when close to sun –& wide base b/c moves faster (travels longer distance along orbit) long when far from sun –& narrow base b/c moves slower (travels shorter distance along orbit) 2nd Law of Planetary Motion: Law of Areas u/distance/sci122/Progra ms/p11/ellipse.html

3rd Law of Planetary Motion: Law of Periods or Harmonic Law P 2 = D 3 –p = time to orbit Sun –d = avg. distance from Sun So, planets that are farther from Sun, take longer to orbit & vice versa. –If know one value, can determine other.

Galileo What were Galileo’s contributions to astronomy? –descriptions of behavior of moving objects invented own telescope –Many discoveries supported Copernicus’ view »Jupiter has moons »Venus  phases b/c orbiting source of light

What did Isaac Newton contribute to astronomy? –explained that gravity kept planets in motion determined by mass & distance btwn 2 objects –What causes force to ↑? »↑ mass or ↓ distance –What causes force to ↓? »↓ mass or ↑ distance Isaac Newton & the Law of Gravitation

perihelion (closest to Sun) more kinetic energy b/c greater gravitational pull by Sun faster to avoid being “sucked in” aphelion (farthest from Sun) more potential energy b/c less gravitational pull slower Isaac Newton & the Law of Gravitation

CT’s Winter −sun appears largest b/c closest (perihelion) CT’s Summer −sun appears smallest b/c farthest (aphelion) Why does the size of the sun appear to change? animation Isaac Newton & the Law of Gravitation How does the Sun’s diameter appear to change with the seasons? −Why?