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Lecture 14
Outline
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Course Evaluations
Neptune and Uranus
Pluto
Kuiper Belt
10-minute break
Discuss Exam 3 and Final
Final review
Course Evaluations
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Course Title = ASTR 111 Section 002.
Instructor’s name = Weigel
You do not need to fill in questions 23-25
Please take time to answer questions on
back:
– What aspects of the course and the way it was
taught helped you to learn?
– What modifications do you suggest for the next
time this course is taught?
– What did you like/dislike about this course?
Suggested Reading
• Chapter 14, all sections
• I will post a practice quiz that will not count
for credit
Doubling the Solar System
• How can you tell the difference between a
planet and a distant star?
– (assume the both span the same angular
distance)
– Name two objects in the sky that are not stars
Uranus
• Hershel “discovered” it
Neptune’s discovery
• A triumph of modern science
The Pioneer anomaly
• Is history repeating itself?
Neptune’s orbit
• Uranus is at about 20 AU and Neptune is
at about 30 AU. The ratio is 3:2. Does
this mean anything?
Neptune
• Galileo missed it
Atmosphere
• Both Uranus and Neptune have atmospheres
composed primarily of hydrogen, helium, and a
few percent methane
• What colors does methane absorb?
Bizarro tilt on Uranus
Exaggerated Seasons On Uranus
• Uranus’s axis of rotation
lies nearly in the plane of
its orbit, producing greatly
exaggerated seasonal
changes on the planet
• This unusual orientation
may be the result of a
collision with a planetlike
object early in the history
of our solar system. Such
a collision could have
knocked Uranus on its
side
Triggering of Storms
Will Uranus always be tilted?
• Neptune looks more active
• But its orbit is 30 AU compared to 20 AU
for Uranus. What is the difference
between amount of energy they receive?
• “Thanks to distance, Neptune
receives less than one-half of the
amount of solar energy than
Uranus.”
• Where did the “one-half” number
come from?
Uranus and Neptune contain a higher proportion
of heavy elements than Jupiter and Saturn
• Both Uranus and Neptune may have a rocky core
surrounded by a mantle of water and ammonia
• Electric currents in the mantles may generate the magnetic
fields of the planets
They should not exist
Bizarro Magnetic Axis
The magnetic
fields of both
Uranus and
Neptune
are oriented
at unusual
angles
• The magnetic axes of both Uranus and Neptune are
steeply inclined from their axes of rotation
• The magnetic and rotational axes of all the other planets
are more nearly parallel
• The magnetic fields of Uranus and Neptune are also offset
from the centers of the planets
Moons and Rings
• un14vi03.mov
Uranus and Neptune each have a
system of thin, dark rings
Discovery of Uranian Rings
Some of Uranus’s satellites show
evidence of past tidal heating
Uranus has five satellites similar to the moderatesized moons of Saturn, plus at least 22 more small
satellites
• Heavily cratered
• Dramatic
topography
• Unfinished tidal
heating?
Triton is a frigid, icy world with a young
surface and a tenuous atmosphere
• Neptune has 13 satellites,
one of which (Triton) is
comparable in size to our
Moon or the Galilean
satellites of Jupiter
• Triton has a young, icy
surface indicative of
tectonic activity
• The energy for this activity
may have been provided
by tidal heating that
occurred when Triton was
captured by Neptune’s
gravity into a retrograde
orbit
• Triton has a tenuous
nitrogen atmosphere
Pluto
Pluto: Problem “Planet”
We almost had 12 planets
• “a planet is any body that orbits a star, is
neither a star nor a satellite of a planet,
and has gravity strong enough to pull it
into a rounded shape”
• … and “a planet must be heavy enough to
clear other objects from its path”
http://www.space.com/scienceastronomy/060819_new_proposal.html
Pluto: Problem “Planet”
Pluto and its moon, Charon, may be
typical of a thousand icy objects that
orbit far from the Sun
• Pluto was discovered after a long search
• Pluto and its moon, Charon, move together in a
highly elliptical orbit steeply inclined to the plane
of the ecliptic
• They are the only worlds in the solar system not
yet visited by spacecraft
• Several hundred small, icy worlds have been
discovered beyond Neptune
• Pluto and Charon are part of this population
Other Objects
A search for a planet between Mars
and Jupiter led to the discovery of
asteroids
• Astronomers first
discovered the asteroids
while searching for a
“missing planet”
• Thousands of asteroids
with diameters ranging
from a few kilometers up
to 1000 kilometers orbit
within the asteroid belt
between the orbits of
Mars and Jupiter
Terminology
• Asteroid – minor planet or planetoid. Orbit
Sun. “Generally bigger than Meteoroid”.
• Meteoroid - "A solid object moving in interplanetary
space, of a size considerably smaller than an asteroid
and considerably larger than an atom or molecule."
• Meteor – “shooing star”. Occurs when
Meteoroid enters the Earth’s atmosphere
• Meteorite – Meteor that survived descent
through atmosphere
Asteroids are found outside the asteroid
belt—and have struck the Earth
• Some asteroids, called near-Earth objects, move in
elliptical orbits that cross the orbits of Mars and Earth
• If such an asteroid strikes the Earth, it forms an impact
crater whose diameter depends on both the mass and
the speed of the asteroid
What are chances of hitting
asteroid as you pass through
asteroid belt?
Comets
• Originate from a belt beyond Pluto or a vast cloud
in interstellar space
• Dusty chunk of ice that partially vaporizes as it
passes near the Sun
Two sources of comets
– Kuiper belt (source of Jupiter family comets)
– Oort Cloud
Kuiper Belt
Comets originate either from a belt beyond Pluto
or from a vast cloud in near interstellar space
• The Oort cloud contains billions of comet nuclei in a spherical
distribution that extends out to 50,000 AU from the Sun
• Intermediate period and long-period comets are thought to
originate in the Oort cloud
• As yet no objects in the Oort cloud have been detected directly
• The Kuiper
belt lies in the
plane of the
ecliptic at
distances
between 30
and 500 AU
from the Sun
• It is thought to
contain many
tens of
thousands of
comet nuclei
Outline
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Course Evaluations
Neptune and Uranus
Pluto
Kuiper Belt
10-minute break
Discuss Exam 3 and Final
Final review
Final
• 3:00-9:30 pm on December 10th (Wednesday)
• About 75-100 multiple choice questions
– About 15-20 questions on Chapters 16 & 17. The rest will
be on material covered on Exams 1-3, with about equal
coverage of material for each Exam.
• Do you need to take the final?
– Your final grade will be the average of your highest three
percentage scores among Exams 1-3 and the final exam.
– If your final percentage score is the lowest, it will be
dropped. If you missed one exam your final grade will be
the average of the three exams you took.
Final Logistics
• Wed. Dec. 10th from 3:00-9:30 pm in Testing and
Tutoring Center.
• IMPORTANT: The Testing and Tutoring Center will be
closed during finals week except for these hours, so if you
miss the exam, I will not be able to give you a make-up
exam.
• During the break, I will have a sign-up sheet for the exam
time slots that are during the normally scheduled exam
time. There will be a 4:30-5:15 slot, a 5:15-6:00 slot, a
6:00-6:45 slot, and a 6:45-7:30 slot.
• The final exam will have 75-100 questions. The exam will
have questions related to the topics covered in the
problems in lecture, problems on the quizzes, and
problems on the first three exams. You will have 120
minutes to complete the exam (but I expect most students
to finish in about 60 minutes).
Final – How to prepare
• Same as for previous exams
• Work through the practice exams and
problems worked in class.
• Make sure that you understand the
principle that the question is asking you
about. (Try to memorize as little as
possible.).
Grade Adjustments
• After the final, I will send out a spreadsheet with
final grades. If there is an error, please email
me.
• I have given two extra credit opportunities, and
for borderline grades, I usually round in the
student’s favor.
• I will not make any adjustments to your grade –
please don’t ask! Especially if this is the first
time you contact me. Especially if you blame me
for your problems.
Final Review