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Chapter

# BurrussAKS2Dec2

Department
Renewable Natural Resources
Course Code
RNR 2001
Professor
All

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Astronomy 1101 Test 2
I. Galileo Galilei and the Scientific Method
A. Basic Information
1. 1564-1642
2. Father of Modern Science
3. First person to observe with a telescope
4. Supported heliocentric model
B. Scientific Method
1. Collect data (experiment, observations)
2. Analyze data (patterns, correlations)
3. Develop an explanation (hypothesis)
4. Find other ways to test the hypothesis
1. The moon
Galileo discovered the moon had mountains and valleys
Objects in the heavens are not smooth, perfect spheres
2. The sun
The sun contains dark spots
The sun rotates
3. Jupiter
Galileo discovered 4 moons around Jupiter (Galilean moons)
4. Venus
Galileo proved that Venus goes through a full set of phases
Not possible in Ptolemaic model
5. Other discovers by Galileo
Saturn has rings (ears)
The Milky Way has thousands (billions) of stars
Heavens are bigger than imagined
D. Inquisition
1. In 1632 wrote Dialogue Concerning the Two Chief World Systems
2. Pope Urban VIII (a friend) sent him before the Inquisition in 1633
3. Sentenced to house arrest for heresy
E. Falling Objects
Galileo tested whether heavier objects fell faster
In a vacuum, objects fall at the same rate
II. Newton: Laws of Motion and Gravity
A. Basic Infrmation
1. 1642-1727
2. Invented reflecting telescopes
3. Invented Calculus
4. Developed Universal law of gravity and 3 laws of motion
B. Three laws
1. First Law
Objects at rest will remain at rest and objects in motion will remain in motion unless
acted upon by an unbalanced force
2. Second Law
Force=Mass X acceleration (F=MA)
Acceleration is the rate of change of something’s velocity

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Mass is how much “stuff” an object has
If you apply the same force to 2 separate masses…
o The low mass object will have high acceleration
o The high mass object will have low acceleration
3. Third Law
For every action, there is an equal and opposite reaction
Whenever one body exerts a force on a second body, the second body exerts the same
force on the first body
C. Newton’s Law of Gravity
Every object attracts every other object with a force that is proportional to the product of
the two masses and inversely proportional to the square of the distance between them
Fgrav =G (m1m2/ r2)
o F=force
o G=gravitational constant
- 6.7 x 10^-11 m3/kg/s2
o m 1,2 masses of the 2 objects
o r distance between the 2 objects
Implications of the Law of Gravity
o Any 2 objects have a gravitational force between them
o The more massive the pair, the larger the force
o As distance increases, gravity goes down
D. Newton and Kepler
1. Newton’s laws prove Kepler’s laws
2. Kepler’s version
o P^2=A^3
3. Newton’s version
o P2 = a3 Å~ 4π2/G(m1+m2)
III. Scale of the Sun and Solar System
A. Phobos and Deimos
With a bike and a ramp, you could jump off of Deimos and into space
One trip around Deimos is about the same as a marathon (26.2 miles)
Most people could throw a baseball out of Phobos’ gravitational field
B. Earth and Moon
Earth’s diameter: 12,756 km
Moon’s diameter: 3,476 km
E/M = 12,756 / 3,476 ≈ 4
Earth is about 4 times the size of the Moon
C. Earth and Moon distance
Earth’s diameter: 12,756 km
Earth-Moon distance: 384,400 km
384,400 / 12,756 ≈ 30
The distance from Earth to the Moon is about 30 times the size of the Earth
D. Earth and Sun Sizes
Earth’s diameter: 12,756 km
Sun’s diameter: 1,392,000 km
S/E = 1,392,000 km / 12,756 km ≈ 110
Properly scaled to the Earth globe, the Sun would need to be 110 feet across
E. Sun to Earth Distance
Sun-Earth dist: 150,000,000 km

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Sun diameter: 1,392,000 km
1.5e8/1.392e6 ≈ 110
in other words, 110 Suns would fit between the Earth and the Sun
IV. Overview of the Solar System
A. What is the Solar System?
The solar system is everything that orbits the Sun
Includes - planets, asteroids, trans-neptunian objects, comets, etc
B. The Sun
By mass, the Sun is the only thing that really matters; the rest is “junk”
o Approximately 99.9% of the total mass in the solar system is in the Sun.
o The Sun “controls” the orbits of everything else
By volume, if you put everything in the solar system together, they would NOT fill up the
Sun.
Orbits of the planets are nearly circular and nearly on the same plane
C. Density
Density = mass/volume
Density of water at sea level = 1000 kg/m3
Density of air at sea level = 1.2 kg/m3
Density of aluminum = 2700 kg/m3
D. Grouping planets
Terrestrial (rocky)
1. Smaller in size and mass
2. Higher average density
3. Made mostly of rocks and metals
4. Solid Surface
5. Few moons and no rings
6. Closer to the sun and each other
7. Warmer
Jovian (gaseous)
1. Larger size and mass
2. Lower average density
3. Made of hydrogen, helium, and hydrogen compounds
4. No solid surface
5. Rings and many moons
6. Farther from the sun and each other
7. Cooler
E. Other
Asteroid Belt (Minor Planets)
o Composed of lots of small rocky objects, mostly between Mars and Jupiter
o Leftovers from formation of solar system
o Largest objects are much smaller than our Moon (similar, but slightly lower density)
Trans-Neptunian Objects (TNO)
o This includes Pluto
o Located in the Kuiper Belt
Extends from the orbit of Neptune (30 AU) out to about 50 AU
o Small icy, rocky objects
o Pluto is a trans-neptunian object, and now considered a dwarf planet
Kuiper Belt
Oort Cloud