Astronomy 1010-H
Planetary Astronomy
Fall_2015
Day-14
Course Announcements
•
How is the sunset/sunrise observing going?
•
Dark Sky nights – Mon. 10/5 & Wed. 10/7 starting at
7:30pm – at the Observatory.
•
Total lunar eclipse: Sun.-Mon. 9/27-28
•
•
•
Weather dependent, if clear, we’ll be setup at the
observatory about sunset.
Here’s the important information
I will collect the L-T workbooks TODAY.
•
Make sure your name is in it.
Kepler’s Third Law
 The size of the orbit determines the
orbital period
 planets that orbit near the Sun orbit with shorter
periods than planets that are far from the Sun
3
a
=
AU
2
P
years
Lecture – Tutorial
rd
Kepler’s 3 Law: pg 25
 Work with a partner!
 Read the instructions and questions carefully.
 Discuss the concepts and your answers with one
another.
 Come to a consensus answer you both agree on.
 If you get stuck or are not sure of your answer, ask
another group.
 If you get really stuck or don’t understand what the
Lecture Tutorial is asking, ask one of us for help.
Which of the following best describes what
would happen to a planet’s orbital speed if it’s
mass were doubled but it stayed at the same
orbital distance?
A. It would orbit half as fast.
B. It would orbit less that half as fast.
C. It would orbit twice as fast.
D. It would orbit more than twice as fast.
E. It would orbit with the same speed.
If a small weather satellite and the large
International Space Station are orbiting Earth at
the same altitude above Earth’s surface, which of
the following is true?
A. The large space station has a longer orbital period.
B. The small weather satellite has a longer orbital period.
C. Each has the same orbital period
CONNECTIONS 3.1
 Copernicus was able
to use right-triangle
trigonometry and
observations of
planets at opposition
or conjunction to very
accurately find their
distances relative to
the Earth–Sun
distance.
CONNECTIONS 3.1
 These distances were
very accurate
compared to our
modern values.
 He was not able to
discern our distance
from the Sun this way,
so the distances are
expressed in units of
our distance (1 AU).
MATH TOOLS 3.1
 The synodic (S) and sidereal (P) periods of
the planets can be related to Earth’s (E)
sidereal period (365.25 days).
 Inferior planets:
 Superior planets:
 Synodic periods are measurable from Earth.
MATH TOOLS 3.2
 Kepler’s third law in its simplest form utilizes
nonstandard units—the periods are in years,
while the distances are in AU.
 The relationship does not change if standard
units are used.
 The equation is just more complicated.
MATH TOOLS 3.3
 Proportionality and inverse proportionality
are ways to understand how one quantity
behaves relative to another quantity.
 It lets you get the gist of how the relationship
works between those two quantities.
 Sometimes, you need to know more than just
the gist—you need to know the constant of
proportionality, which exactly relates the
quantities.
 Galileo Galilei was
the first scientist to
observe the sky with
a telescope.
 Found four moons in
orbit around Jupiter.
 Saw that Venus had
phases.
• In a geocentric
model, Venus’s
phase would not
change.
Isaac Newton
(1642 – 1727)
The Baddest
Dead White Guy
of Them All
Isaac Newton
(1642 – 1727)
1. Probably died a virgin
2. Was a priest and Lawyer
3. Had artificial wooden and silver noses
4. Probably died of Mercury poisoning
5. Rumored to have died when his bladder burst
6. Was blind at the time of his death
7. Was labelled a heretic by the church
Isaac Newton
(1642 – 1727)
1.
2.
3.
4.
5.
6.
7.
Probably died a virgin
Was a priest and Lawyer
Had artificial wooden and silver noses
Probably died of Mercury poisoning
Rumored to have died when his bladder burst
Was blind at the time of his death
Was labeled a heretic by the church
 Using observations
and investigations
from Galileo, Isaac
Newton discovered
laws that apply to all
objects.
 Basis of classical
mechanics.
 Physical laws, not
empirical science.
Newton’s First Law of Motion
• A body remains at rest or moves in a straight line at
a constant speed unless acted upon by an outside
(net) force.
• A rockets will coast in space along a straight line at
constant speed.
• A hockey puck glides across the ice at constant
speed until it hits something
Newton’s Second Law of Motion
• (net)Force = mass x acceleration or
Fnet = m x a
• Acceleration is the rate of change in velocity – or
how quickly your motion is changing.
• Three accelerators in your car!!
 Acceleration is force divided by mass, or
a
F
m
 Mass resists changes in motion.
 Greater forces mean greater accelerations.
MATH TOOLS 3.3
 Proportionality and inverse proportionality
are ways to understand how one quantity
behaves relative to another quantity.
 It lets you get the gist of how the relationship
works between those two quantities.
 Sometimes, you need to know more than just
the gist—you need to know the constant of
proportionality, which exactly relates the
quantities.
MATH TOOLS 3.4
 Knowing the
unbalanced force
an object
experiences
allows you to find
its acceleration,
and vice versa.
Newton’s Third Law of Motion
• Whenever one body exerts a force on a second
body, the second body exerts an equal and opposite
force on the first body.
• Don’t need a rocket launch pad!
• The Bug and the Windshield – who is having the
worse day?
 Newton’s third law
of motion: For every
force, there is an
equal and opposite
force.
 The two forces have
the same size.
 The two have
opposite directions.