Transcript Chapter 25.1: Models of our Solar System

Chapter 25.1: Models of our
Solar System
Objectives:
•Compare & Contrast geocentric and
heliocentric models of the solar sytem.
•Describe the orbits of planets explain how
gravity and inertia keep the planets in orbit.
•Name the components of the solar system.
Answer these questions on the top of your Guided
Reading Worksheet.
1. What is the difference between the
geocentric and heliocentric models of the
solar system? Which one is accurate?
2. Saturn is 10 x farther from the sun than
Earth. What is the distance between
Saturn and the sun in AU? In kilometers
or miles? (show your work)
3. The Andromeda galaxy is 2.5 million light
years away. How long does it take the
light from Andromeda to reach us ?
1. Models of the Solar System
Ancient people thought …
•
E. is stationary; Sun, planets, & stars
move around E.
•
Observed 5 planets: Mercury; Venus;
Mars; Jupiter; & Saturn
A. Geocentric Model = Earth is the center
of the universe (a sphere). Stars & planets
orbit E. each day.
• Who: Most ancient Greeks
… later Ptolemy (Egyptian –
140 AD) maps out position
of planets with this model
(Accepted for ~1400 yrs)
• Earth is stationary.
• fixed # of stars.
A. Geocentric Model: Ptolemy’s Epicycles
When E. passes planets – they look like they are moving
backwards relative to us for a while. This apparent (not
actual) backward motion in known as “retrograde motion”.
Ptolemy didn’t believe E. moved (it was the center of the
universe) – so he couldn’t explain this “backward” motion of
planets. That’s where Epicycles come in – but they are not
real.
Geocentric model cont.
• Problems with Geocentric Model
1. It’s WRONG! But also …
2. Earth is not stationary (It rotates)
3. It could not explain the motion of planets … so
Ptolemy created “EPICYCLES” to explain
planetary motion.(Especially RETROGRADE
motion)
See Epicycles: zebu.uoregon.edu/.../121/lecture-3/ptolemy.html
B. Heliocentric Model = Sun is the center of
universe. Earth orbits the sun.
• Aristarchus – Ancient Greece
Proposes theory. Not widely
accepted.
• Nicolaus Copernicus –1543 AD
Thinks Aristarchus had the
right idea and develops it
into a publication.
Problem w/Copernicus’s
Model: Orbits are not perfect
circles.
Retrograde Motion of Mars
http://www.sciencemaster.com/space/item/helio_2.php
http://www.astro.utoronto.ca/~zhu/ast210/both.html
B. Heliocentric Model: Galileo
• Galileo – 1616, 1632 Publications
– Explains how Inertia & Gravity keep planets in
motion.
Finds Evidence to Support Copernicus’s
Heliocentric Theory
– Venus has phases (new & full can’t be seen b/c sun
blocks … Venus must move around the sun, not
Earth).
– Jupiter’s moon’s: Galileo discovers 4 moons orbiting
Jupiter … NOT EARTH (Earth must not be at the
center of the UNIVERSE).
http://astronomyonline.org/SolarSystem/GalileanMoons.asp?Cate=SolarSystem&SubCate=Jupiter&SubCate2=JT02
– Reward: House arrest for life.
2. Planetary Orbits: Inertia & Gravity keep
planets moving in a curved path.
1. INERTIA: Newton 1st Law of Motion tells us that planets want to
keep moving in a straight line forever (in motion … stay in motion)
GRAVITY: The Sun’s gravitational pull keeps planets
fr. Moving in a straight line. This tugging creates the
curved path.
Gravity is an attractional force between two masses.
2.
Gravity: pulls on Earth
Inertia: Earth want to keep moving in a straight line
(moving keep moving, in same direction). The force that
prevents this: Gravitational force from sun.
2. Planetary Orbits
• Johannes Kepler
(1600) revises
Copernicus’s model
– Orbits are not circles
… they’re ELLIPSES
(OVAL)
– Planets orbit the sun in
a plane called the:
ECLIPITIC
3. Components of the Solar System
Solar System = Sun, planets, their moons
(satellites),asteroids, kuiper belt objects, &
comets (All orbit sun)
Sun
Mercury
Venus
Earth
Mars
Asteroid Belt
Jupiter
Saturn
Uranus
Neptune
* Pluto
Kuiper Belt Objects
Comets
3. Components of the Solar System
A.U. (Astronomical Units) =
•average distance between Earth & sun (1 AU)
•93 million miles (149.6 million km)
•Used to measure distances w.in S.system
•Jupiter is 5 AU from sun … its 5 x farther fr. Sun
than E.
Distances Within the Solar System
Planet
Mercury
Distance from
Distance in A.U.s
Sun in kms
57,900,000
0.387
Venus
Earth
Mars
Jupiter
Saturn
108,200,000
149,600,,000
227,900,000
778,400,000
1,427,000,000
0.723
1.000
1.524
5.203
9.539
Uranus
Neptune
Pluto
2,896,600,000
4,520,000,000
5,899,900,000
19.182
30.214
39.439
4. Exploring the Solar System
A. Telescopes; spacecraft; space probes
B. Manned Missions to the Moon
July 20 1969: Apollo 11 touches down on moon (Neil
Armstrong)
Apollo 17 – last mission