Lecture 14

Outline• Course Evaluations• Neptune and Uranus• Pluto• Kuiper Belt• 10-minute break• Discuss Exam 3 and Final• Final review

Course Evaluations

• 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 proportionof 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 Neptuneare 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 moderate-sized 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 Plutoor 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• 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