Origin of Modern Astronomy

Chapter 22

22.1 Early Astronomy

A. Ancient GreeksAristotle- Earth is round because it casts a curved shadow on the Moon. (Luna eclipse)

22.1 Early Astronomy

A. Ancient GreeksEratosthenes- measured the earth’s diameter.

22.1 Early AstronomyA. Ancient Greeks

Hipparchus (2nd century B.C.)Star chart of 850 stars

22.1 Early AstronomyA. Ancient GreeksGeocentric Model- earth centered and all

objects “orbit” about the earth.Heliocentric Model- Sun centered

22.1 Early AstronomyA. Ancient GreeksPtolemaic System-PtolemyNeeded “epicycles” to makeplanets “retrograde”

22.1 Early AstronomyB. Birth of Modern AstronomyNicolaus Copernicus (1473-1543)Supported the Heliocentric Model in opposition

of the Church.

22.1 Early AstronomyB. Birth of Modern AstronomyTycho Brahe (1546-1601)Very precise positions of Mars

Johannes Kepler (1571-1630)Used Brahe’s information to discover3 planetary laws.

22.1 Early AstronomyB. Birth of Modern AstronomyKepler’s Planetary Motion Laws1. Move in ellipses. 2. Sweep out equal sectors in equal time.3. Distance from Sun determines period of orbit.

22.1 Early AstronomyB. Birth of Modern AstronomyGalileo Galilei (1564-1642) Pointed at telescope

toward the stars…..1. 4 satellites about Jupiter2. Planets were discs not pinpoints3. Venus had “phases”4. The Moon was not smooth5. The Sun had “spots”

22.1 Early AstronomyB. Birth of Modern AstronomySir Isaac Newton (1642-1727)Described laws of motion. First-

inertia.Formulated and tested the

Universal Law of GravitationGravity directly proportional to

mass and inversely proportional to square of distance

22.2 Earth-Moon-Sun SystemA. Motions of EarthRotation-spin (1 day)Revolution-moves around Sun (1 yr.)Precession-swing about the axis (26 000 yr.)

22.2 Earth-Moon-Sun SystemA. Motions of EarthRotationSolar Day-time Sun returns to same

position. About 24 hoursSidereal Day- turn 360o, 23h 56m 4s

22.2 Earth-Moon-Sun SystemA. Motions of EarthRevolution

Perihelion- 150 million kmAphelion- 152 million km

22.2 Earth-Moon-Sun SystemA. Motions of EarthRevolution

Seasons because of axis tilt

22.2 Earth-Moon-Sun SystemA. Motions of EarthPrecession26 000 years

Change of tilt21.5o to 24.5o

41 000 years

22.2 Earth-Moon-Sun SystemA. Motions of EarthSolar System moving toward Vega at

20 km/s.

Revolve aboutthe Milky Wayat 250 km/s230 million year

22.2 Earth-Moon-Sun SystemB. Earth-Moon SystemPerigee-closestApogee-farthest

22.2 Earth-Moon-Sun SystemB. Earth-Moon SystemPhases of the Moon

22.2 Earth-Moon-Sun SystemB. Earth-Moon SystemSynodic month- 29 ½ days

(Roman calendar)Sidereal month-27 1/3 days2 more days to make a New Moon Revolves at 27 1/3days. (same side)

22.2 Earth-Moon-Sun SystemB. Earth-Moon

SystemEclipses

Full Moon-LunaNew Moon- Solar

http://eclipse.gsfc.nasa.gov/eclipse.html

22.3 Earth’s MoonFacts:3475 km diameter3.3x dense as water1/6 G or 150 lbs man=

25 lbs on Moon

A. Lunar Surface: dark lowlands

bright highlands

22.3 Earth’s MoonA. Lunar Surface: Craters- impacts by

space debris

22.3 Earth’s MoonA. Lunar Surface: Craters- Bright rays

are created by recent impacts.

22.3 Earth’s MoonA. Lunar Surface: Highlands:Some mountains are 8

km high.

22.3 Earth’s MoonA. Lunar Surface: Maria: basaltic lava

that “bleed out”Rilles- lava flows

22.3 Earth’s MoonA. Lunar Surface: Regolith: ignous

rock , beads and dust.

22.3 Earth’s MoonA. Lunar History Most accepted

model is Mars sized body collided with Earth.