Download Day-14

Astronomy 1010
Planetary Astronomy
Fall_2015
Day-14
Course Announcements
•
Dark Sky nights – Mon. 10/5 & Wed. 10/7 starting at
7:30pm – at the Observatory.
•
Total lunar eclipse: Sun.-Mon. 9/27-28
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•
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Weather dependent, if clear, we’ll be setup at the
observatory about sunset. If you come out after dark, turn
your headlights OFF before you come around the last bend.
Here’s the important information
L-T workbooks will be picked up TODAY.
Make SURE your name is in the book.
Kepler’s First Law: The orbit of a planet about
the Sun is an ellipse with the Sun at one focus.
Kepler’s Second Law: A line joining a planet and
the Sun sweeps out equal areas in equal intervals
of time.
i-Clicker Question
According to Kepler’s second law, a planet with an
orbit like Earth’s would:
A. move faster when further from the Sun.
B. move slower when closer to the Sun.
C. experience a dramatic change in orbital speed
from month to month.
D. experience very little change in orbital speed over
the course of the year.
E. none of the above.
Another i_Clicker ?
Kepler’s second law says “a line joining a planet and the Sun
sweeps out equal areas in equal amounts of time.” Which of
the following statements means nearly the same thing?
A. Planets move fastest when they are moving toward the Sun.
B. Planets move equal distances throughout their orbit of the
Sun.
C. Planets move slowest when they are moving away from the
Sun.
D. Planets travel farther in a given time when they are closer
to the Sun.
E. Planets move the same speed at all points during their orbit
of the Sun.
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
p = ~ 12 years
p = 1 year
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
MASS DOES NOT MATTER
Both have p = 1 year
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
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.
 Consequences:
• Distant planets take
longer to orbit the
Sun.
• Distant planets travel
at slower speeds.
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.
Another i_Clicker query
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.
And 1 more …
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.
 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.