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TRANSCRIPT
Ch. 22 Origin of Modern Astronomy
Pretest
1. True or False:
Early Greek astronomers (600 B.C.–A.D. 150) used
telescopes to observe the stars.
Ch. 22 Origin of Modern Astronomy
Pretest
2. What lies at the center of our solar system?
a. the sun
b. Mars
c. Earth
d. the moon
Ch. 22 Origin of Modern Astronomy
Pretest
3. What is rotation?
Ch. 22 Origin of Modern Astronomy
Pretest
4. What is the approximate time that it takes Earth to
rotate on its axis?
a. 12 hours
b. 24 hours
c. 30 days
d. 365 days
Ch. 22 Origin of Modern Astronomy
Pretest
5. What was the most important accomplishment of the
Apollo moon missions?
Ch. 22 Origin of Modern Astronomy
Pretest
6. Approximately how long does it take for the moon to
go through all of its phases?
a. 12 hours
b. 24 hours
c. 30 days
d. 365 days
Ch. 22 Origin of Modern Astronomy
Pretest
You will be able to… •Describe the contributions of ancient Greeks to astronomy.
•Compare and Contrast the geocentric and heliocentric models
of the solar system
22.1 Early Astronomy
22.1 What is Astronomy
Astronomy is the science that studies the
universe. It includes the observation and
interpretation of celestial bodies and
phenomena.
Astrolabe
Astrolabes are used to
show how the sky looks at a
specific place at a given
time.
iPhone App: Astrock, the Astronomical Clock 1.0
22.1 Geocentric vs. Heliocentric
22.1 Geocentric vs. Heliocentric
Geocentric Model • Geo (Latin and Greek prefix) = “Earth”
• Centric (is from the Greek word kentrikos) = “located in the center”
• Geocentric means “having Earth as the center.”
• In the ancient Greeks’ geocentric model, the
moon, sun, and the known planets—Mercury,
Venus, Mars, and Jupiter—orbit Earth.
With the naked eye, one can see five planets:
Mercury, Venus, Mars, Jupiter, and Saturn.
• In the photo at the right,
you can see (from top to
bottom) Saturn, Venus,
Jupiter, and Mercury in
alignment with the
recently set Sun.
22.1 Geocentric vs. Heliocentric
Heliocentric Model
• Helio (is a Latin and Greek prefix) = “Sun”
• In the heliocentric model, Earth and the other
planets orbit the sun.
22.1 Ancient Greeks
1) Aristotle • Greek (384 – 322 B.C.)
• He concluded that the earth was round because
it always casts a curved shadow on the moon.
22.1 Ancient Greeks
2) Ptolemy • Ptolemy created a model of the universe that
accounted for the movement of the planets.
(geocentric model)
• Retrograde motion is the apparent westward
motion of the planets with respect to the stars.
Retrograde Motion
Retrograde Motion
The image below displays the actual retrograde motion of Jupiter
(brighter) and Saturn (dimmer) over eleven months:
22.1 The Birth of Modern Astronomy
3) Nicolaus Copernicus • Copernicus concluded that Earth is a planet. He
proposed a model of the solar system with the
sun at the center. (Heliocentric model)
22.1 The Birth of Modern Astronomy
4) Johannes Kepler (1 of 2)
• Kepler discovered three laws of planetary motion:
1. Orbits of the planets are elliptical.
2. Planets revolve around the sun at varying
speed.
3. There is a proportional relationship between
a planet’s orbital period and its distance to
the sun.
http://janus.astro.umd.edu/SolarSystems/
22.1 The Birth of Modern Astronomy
4) Johannes Kepler (2 of 2)
• An astronomical unit (AU) is the average
distance between Earth and the sun; it is about
150 million kilometers.
Planet Revolution
22.1 The Birth of Modern Astronomy
5) Galileo Galilei • Galileo’s most important contributions were his
descriptions of the behavior of moving objects.
• He developed his own telescope and made
important discoveries:
1. Four satellites, or moons, orbit Jupiter.
2. Planets are circular disks, not just points of light.
3. Venus has phases just like the moon.
4. The moon’s surface is not smooth.
5. The sun has sunspots, or dark regions.
22.1 The Birth of Modern Astronomy
6) Sir Isaac Newton • Newton was the first to formulate and test the law
of universal gravitation.
Universal Gravitation
• Gravitational force decreases with distance.
• The greater the mass of an object, the greater is
its gravitational force.
If the airplane weighs 10000 pounds on the surface of the earth, it weighs 9965 pounds at 35000 feet.
Gravity’s Influence on Orbits
You will be able to… •Describe the contributions of ancient Greeks to astronomy.
•Compare and Contrast the geocentric and heliocentric models
of the solar system
22.1 Early Astronomy