Origin of Modern Astronomy
Chapter 22
22.1 Early Astronomy
A. Ancient Greeks
Aristotle- Earth is round because it casts a
curved shadow on the Moon. (Luna eclipse)
22.1 Early Astronomy
A. Ancient Greeks
Eratosthenes- measured the earth’s
diameter.
22.1 Early Astronomy
A. Ancient Greeks
Hipparchus (2nd century B.C.)
Star chart of 850 stars
22.1 Early Astronomy
A. Ancient Greeks
Geocentric Model- earth centered and all
objects “orbit” about the earth.
Heliocentric Model- Sun centered
22.1 Early Astronomy
A. Ancient Greeks
Ptolemaic System-Ptolemy
Needed “epicycles” to make
planets “retrograde”
22.1 Early Astronomy
B. Birth of Modern Astronomy
Nicolaus Copernicus (1473-1543)
Supported the Heliocentric Model in opposition
of the Church.
22.1 Early Astronomy
B. Birth of Modern Astronomy
Tycho Brahe (1546-1601)
Very precise positions of Mars
Johannes Kepler (1571-1630)
Used Brahe’s information to discover
3 planetary laws.
22.1 Early Astronomy
B. Birth of Modern Astronomy
Kepler’s Planetary Motion Laws
1. Move in ellipses.
2. Sweep out equal sectors in equal time.
3. Distance from Sun determines period of orbit.
22.1 Early Astronomy
B. Birth of Modern Astronomy
Galileo Galilei (1564-1642) Pointed at telescope
toward the stars…..
1. 4 satellites about Jupiter
2. Planets were discs not pinpoints
3. Venus had “phases”
4. The Moon was not smooth
5. The Sun had “spots”
22.1 Early Astronomy
B. Birth of Modern Astronomy
Sir Isaac Newton (1642-1727)
Described laws of motion. Firstinertia.
Formulated and tested the
Universal Law of Gravitation
Gravity directly proportional to
mass and inversely
proportional to square of
distance
22.2 Earth-Moon-Sun System
A. Motions of Earth
Rotation-spin (1 day)
Revolution-moves around Sun (1 yr.)
Precession-swing about the axis
(26 000 yr.)
22.2 Earth-Moon-Sun System
A. Motions of Earth
Rotation
Solar Day-time Sun returns to same
position. About 24 hours
Sidereal Day- turn 360o, 23h 56m 4s
22.2 Earth-Moon-Sun System
A. Motions of Earth
Revolution
Perihelion- 150 million km
Aphelion- 152 million km
22.2 Earth-Moon-Sun System
A. Motions of Earth
Revolution
Seasons because of axis tilt
22.2 Earth-Moon-Sun System
A. Motions of Earth
Precession
26 000 years
Change of tilt
21.5o to 24.5o
41 000 years
22.2 Earth-Moon-Sun System
A. Motions of Earth
Solar System moving toward Vega at
20 km/s.
Revolve about
the Milky Way
at 250 km/s
230 million year
22.2 Earth-Moon-Sun System
B. Earth-Moon System
Perigee-closest
Apogee-farthest
22.2 Earth-Moon-Sun System
B. Earth-Moon System
Phases of the
Moon
22.2 Earth-Moon-Sun System
B. Earth-Moon System
Synodic month- 29 ½ days
(Roman calendar)
Sidereal month-27 1/3 days
2 more days to
make a New Moon
Revolves at 27 1/3
days. (same side)
22.2 Earth-Moon-Sun System
B. Earth-Moon
System
Eclipses
Full Moon-Luna
New Moon- Solar
http://eclipse.gsfc.nasa
.gov/eclipse.html
22.3 Earth’s Moon
Facts:
3475 km diameter
3.3x dense as water
1/6 G or 150 lbs man=
25 lbs on Moon
A. Lunar Surface:
dark lowlands
bright highlands
22.3 Earth’s Moon
A. Lunar Surface:
Craters- impacts by
space debris
22.3 Earth’s Moon
A. Lunar Surface:
Craters- Bright rays
are created by
recent impacts.
22.3 Earth’s Moon
A. Lunar Surface:
Highlands:
Some mountains are 8
km high.
22.3 Earth’s Moon
A. Lunar Surface:
Maria: basaltic lava
that “bleed out”
Rilles- lava flows
22.3 Earth’s Moon
A. Lunar Surface:
Regolith: ignous
rock , beads and
dust.
22.3 Earth’s Moon
A. Lunar History
Most accepted
model is Mars sized
body collided with
Earth.