Introduction to Astronomy

Spring 2017

This picture from a Press Release issued in February of 2016 shows the measurements that resulted in the first discovery of gravitational waves from the inspiral of two black holes that merged into one bigger black hole. This is the most spectacular result in astronomy in the past few years and is widely expected to win a Nobel Prize for the team leaders. The red and blue wiggly lines show the signal: They are measurements of the wiggle in the length of one 2.5-mile-long arm of the Laser Interferometer Gravitational Wave Observatory (LIGO) stations at Hanford, Washington (red line) and Livingston, Louisiana (blue line). The agreement of the two measurements is critical to our confidence that the measurements are correct and detecting a distant astronomical object; the time difference between them (removed to make this illustration) is (as expected) the light travel time between the two stations as seen from the direction of the two black holes. Here's the mind-blowing point: The maximum wiggle in the 2.5-mile arm length is 4/1000 of the diameter of a proton - a tiny subatomic particle. This is proportionally equivalent to detecting a wiggle of the width of a human hair in the 4.3-light-year distance to the nearest star outside of our Solar System. It is by far the most accurate measurement ever achieved by science.

Note that this is not the measurement of the size of any physical object. Rather, it is a measurement of how much space itself expanded and contracted as a gravitational wave passed by. The data sequence is 0.3 seconds long (horizontal width). The wave was formed by two black holes that revolved around each other at a rate of about 30 orbits per second when the signal becomes visible above the wiggly noise to about 250 orbits per second just before the black holes merged and the signal disappears. Why did the orbital time decrease? Because orbital energy was emitted in the gravitational wave. Then the black holes got closer together and moved faster. They were moving at about 1/2 of the speed of light just before they merged. When the black holes got close enough together to touch, they merged into one bigger black hole. During the last moments of the inspiral, a part of the black holes' masses (about 3 times the mass of our Sun) was converted into energy and radiated away in the gravitational wave with a maximum power of about 50 times the total power of all the stars in the observable Universe combined. Only a very, VERY tiny fraction of this power reached the detectors on Earth, because the two black holes were 1.3 billion light years away, and the gravitational radiation was emitted in all directions. The black holes initially had masses of 29 and 36 times the mass of our Sun, and the remnant black hole after they merged has a mass of 62 times the mass of our Sun.

Gravitational waves were predicted 100 years before this discovery by Albert Einstein as a consequence of his General Theory of Relativity - that is, his theory of gravity. This detection is the strongest test of that theory that scientists have ever made. The theory passes the test. This is not only a vindication of Einstein's theory, it is also a robust proof that black holes really exist.

This image will be featured in Lecture 12 of the course on February 28th.

Final Update: Wednesday, May 3, 2017

Final grades have been computed. They will be posted on Canvas on Friday, May 5th and will be submitted to the University next week.

The final grade curve used to compute letter grades was exactly as posted all semester and as posted below. The course is now finished and grades cannot be changed. Please do not send me emails asking for extra credit. If I give extra credit to some people, then I have to give it to everybody, and this just forces me to change the grade curve. I promised on the first day of classes that I would not change the grade curve, and I have kept that promise.

The distribution of grades is typical for my classes: 14 % of the class got A or A-; 32 % got B+, B, or B-; 36 % got C+, C, or C-; 16 % got D or D- (nobody got D+), and 2 % (one person) got an F. Note that the above distribution does not take recent course drops into account, nor does it take account of the fact that some people (often ones with relatively low grades) took the course for CR/NO CR. Any grade of D- or better converts to a CR for these people.

Many people saved a passing grade via Test 6, as I expected. Ten people got their highest scores on Test 6. You may be interested to know that the average homework score was the highest score for 13 people. I always tell classes on the first day that it is worth doing the homework, because students usually do well on it. Also, Exam 4 was the highest score for 10 people even though it covered the most difficult section. Recall that it was the third of three consecutive tests during three consecutive classes. I strongly suspect that the good results on Exam 4 show the importance of repeated study of a subject. The good results on Exam 6 are, I am sure, a consequence of the fact that -- again as promised -- the last section is the easiest one of the course.

Tomorrow's lecture (Thursday, May4) on the history of life on Earth and on possible life elsewhere in the Universe will take place as scheduled. I hope that you will come, even though it cannot affect your grade. I think that this is the most interesting lecture of the course.

I hope that you enjoyed the course, and I wish you all the best in everything that you do.

Unique number: Section 47791
Classes: Tuesday and Thursday at 3:30 - 5 PM in Welch 1.308
Instructor: John Kormendy 
Office: RLM 15.326
Office Hours: Wednesday 2 - 4 PM in RLM 15.326
Office Telephone: 512 - 471 - 8191 (Please don't leave phone messages; send email instead.)
Teaching Assistant: JinGyu Ock (Grade Recorder)
Office: RLM 13.126
Office Hours: Thursdays at 1 - 3 PM in RLM 15.202

Spring 2017 syllabus as a jpeg file or as a pdf file

Schedule of help sessions in 2017 (Note that times and places vary):

TA's Help Session for Homework 1: Wednesday, February 1, 2017 from 4 to 6 PM in Welch 3.502

John Kormendy's Help Session for Homework 2 and Test 2: Monday, February 27, 2017 from 4 to 6 PM in Welch 3.502

John Kormendy's Help Session for Exam 1: Monday, February 6, 2017 from 4 to 6 PM in RLM 4.102

John Kormendy's Help Session for Exam 2 is cancelled. It was originally scheduled on Wednesday, March 1, 2017 from 4 to 6 PM in Welch 3.502

John Kormendy's Help Session for Exam 3: Monday, March 6, 2017 from 4 to 6 PM in RLM 4.102

There is no help session for Exam 4.

John Kormendy's Help Session for Exam 5: Wednesday, April 5, 2017 from 4 to 6 PM in Welch 2.246

John Kormendy's Help Session for Exam 6: Monday, May 1, 2017 from 4 to 6 PM in RLM 4.102

Powers of Ten Tutorial

This is a Java tutorial that gives you some feeling for the scales of things (both large and small) that we will discuss.

Time zone map

There are small inconsistencies between the above map and the one that I show in class, e. g., in Australia, where the posted map does not show three, half-hour time zones meeting at one place. Countries frequently make changes in their time zones; the posted map (from 1997) is slightly out of date. During the 2000 Millennium celebration, the time zones were as I show them in class.

Applet demo of the retrograde motion of Mars

Applet illustrating the Doppler effect

Applet illustrating observations of binary stars

Mars: A selection of Mars Global Surveyor images

Mars: Evidence for recent liquid water

Mars: Browsable pictures from orbit -- like Google Earth -- showing stunning detail. Try both "Visual" and "Elevation". The elevation maps come from satellite radar altimeters.

Mars: NASA homepage for the Opportunity rover on Mars

Annular eclipse of the Sun by Mars's moon Phobos as seen from the surface of Mars by the Mars Exploration Rover Opportunity

Hubble Galaxy Classification "tuning fork" diagram constructed from Sloan Digital Sky Survey pictures

Hubble Galaxy Classification "tuning fork" diagram constructed from Sloan Digital Sky Survey pictures (bigger version)


This course is an introduction to astronomy for non-science majors. We start with explanations of the seasons on Earth and of what you see when you look up at the sky. Two lectures cover the history of astronomy from the ancient Greeks until the Renaissance. The history of astronomy is also the history of the development of the way that we do science; we will see why science is so successful in teaching us new things. Throughout the course, I try to show you how we learn things about our Universe. I then discuss stars - their formation, life histories, and deaths. This section includes a discussion of our Sun. From stars, we expand our horizons to the study of galaxies of stars and of the Universe as a whole. We look back in time to the beginning of the Universe to give us perspective on how everything around us was created - everything from the stuff that you and I are made of all the way out to the most distant stars. Given this perspective, we then return home to our Solar System. I describe the planets, moons, comets, and asteroids, and I put our planets into context by comparing them to the planets that astronomers are now finding around other stars. All this leads up to a discussion of our Earth, of the history of life on Earth, and of the prospects that there is life elsewhere in the Universe. The emphasis throughout the course will be on conceptual understanding of the "big picture". You will be astonished by how much we can learn about places far away and long ago.


It helps if you had high school science courses, but I do not expect this or require it. I will - as much as possible - start each subject from the beginning. There is only a little math in the course, and even people who have "math anxiety" usually find that the math is not a big problem. I will use "scientific notation" for large and small numbers, and I will introduce about half-a-dozen equations that describe how nature behaves. You never need to memorize equations. If you need them on exams, I will give them to you. But you need to understand what they mean and how to use them. Here is a question that is typical of the reasoning that you may be asked to apply: Your SUV has a 20 gallon tank for gasoline, and you can drive 24 miles with one gallon of gas. If you want to drive 1000 miles, how many times will you have to fill the tank? Most of the mathematical reasoning involves ratios and proportions, and all of the arithmetic that I ask you to do during exams can be done without a calculator.


Horizons: Exploring the Universe by Michael Seeds and Dana Backman, published by Brooks/Cole and available at the Co-Op. You can get the 11th, 12th, 13th or 14th Editions. Older editions are not bad. If you get one, then you will have to be careful about reading assignments: the pages and section numbers mentioned in assignments will correspond to the 13th Edition and may not correspond to those in earlier editions. Important: Buying the text is optional. Most people find it helpful to have a textbook in which they can read another author's description of the things that we talk about in class. However, all class slides will be posted on this class web site. Therefore, you can get through this course without having a textbook if you study and understand the material that I cover in class.


VERY IMPORTANT: I strongly recommend that you attend classes. Astronomy is not intrinsically difficult, but it is probably unfamiliar to you, and it is much harder to understand the material if you only read about it. Also, I will omit some subjects that are in the book, and I will lecture on other subjects that are not in the book. You will be responsible for the content of the lectures. I will post the lecture slides well in advance. Don't let the convenience of posted slides and lectures fool you into thinking that you can skip class. The in-class lectures are an important part of the education experience. If you skip classes and study only from the postings, chances are that you will pass the course but that your grade will be lower than it could have been. This is not because I am nasty to people who skip classes (I'm not) but rather because you will not know the material as well.


If you have trouble understanding something in the course, please ask questions in class or come and see me. I will be happy to discuss the problem with you. The TAs are also available. Review sessions will be scheduled prior to exams and homework due dates.


even if I am out of town. Astronomy is an observational science. My research depends in part on visits to various observatories, including the University's McDonald Observatory in west Texas. Also, occasionally, I have to attend an out-of-town meeting. If I miss a class for these or any other reasons, the class will meet as usual.


You may be interested in the Astronomy Department's regular evening star parties, when you can see some of the objects that we discuss in class through one of our telescopes. They happen on Wednesday nights on the roof of RLM and on Fridays and Saturdays at Painter hall. Please see this link for details..


The University of Texas at Austin provides upon request appropriate academic accommodations for qualified students with disabilities. For more information, contact the Office of the Dean of Students at 471-6259, 471-4641 TTY. Also, please notify me of any modification/adaptation that you may require to accommodate a disability-related need. Specialized services are available on campus through Services for Students with Disabilities.


There will be 6 in-class exams (see the syllabus). Four of these will follow and cover the 4 major sections of the course. Tests 3 and 4 just before Spring Break essentially are makeup exams that follow Section 2. So the first half of the class will end with 3 exams over 3 class days (with 2 help sessions) ending at the start of Spring Break. If you take all 6 exams and do all the homework, you will have 7 scores, each worth 20 % of your final grade. We will then drop your lowest 2 scores and average the rest. There will be no final exam. There is no penalty for missing an exam or the homework as long as you get 5 total grades (either 4 exams and the homework or 5 exams and no homework). For this reason, there will be no makeup exams, not even for valid reasons such as medical or family emergencies.


If a class is cancelled by the University because of bad weather (usually snow and ice), then that will use up one of the extra test times. There will be no other makeup tests for bad weather. This is why you get 6 total tests, so that we can lose one test because of unforeseen circumstances. Bad weather is an unforeseen circumstance like any other; the only difference is that it affects all of us. But note that, if you take all tests and do the homework, you get 2 grade drops. So even losing one test because of bad weather will not result in a loss of all of your flexibility with exams. Even if we lose one class because of bad weather, you still get a total of 5 tests and you still need only 4 tests plus your homework to make up a complete final grade. So even then, we drop one (lowest) grade.


I emphasize again: THERE WILL BE NO MAKEUP EXAMS, EVEN FOR VALID (E.G., MEDICAL) REASONS. Please don't ask. I will be polite, but the answer will have to be "no".


Homework assignments will have a due date that is 2 weeks from when the homework is distributed. Late homework will not be accepted unless you have given me and I have accepted your reason for requesting an extension prior to the due date. No homework will be accepted after I have discussed the answers in the help session that preceeds each exam. Homework is optional (see below).

Here's another description of how we will get your final grade: You can get 7 scores, each of which counts 20 percent of your grade, for 6 tests and two homeworks averaged together. We will then drop your lowest score and add up the other 5. This means that you can decide not to do the homework and still be OK if you take all the tests. But if you miscalculate and have to miss 2 tests AND you decided not to do the homework, then I cannot help you to make up a fifth score by giving you a makeup exam or other extra credit work. So think carefully before you decide not to do the homework.

If you decide to do the homework, please make sure that you do both homework assignments.

Exam dates: The syllabus lists the dates of the exams. I promise not to change these dates. Please note the dates of the exams, since it is impractical to schedule makeups.

There will be no final exam.

Copying during exams is a crime for which the punishment will be at least an F for that exam and very possibly an F for the course. I will not hesitate to report cheating to the Dean of Students. University standards of academic integrity are posted here.

All work handed in for grading must be your own work. It is OK to discuss homework with a friend, but it is important to use your own thoughts and words in writing your answers. If you are puzzled by a question, do not copy a friend's answer. Instead, please discuss the problem with me or with a TA. Don't be shy! We are here to help!

If we see evidence for copying, such as two detailed but identical answers, then both students will get zero for that question. In cases of widespread copying, both students will get zero for the whole homework and may get reported to Student Judicial Services.

Recommendation: When you write homework solutions, show intermediate steps; don't just write down the answer. When the TA grades the homework, he or she needs to see how you thought about the problem. If you get the wrong answer but thought about at least some of the problem correctly, you get partial marks. If the intermediate steps are not shown and the answer is wrong, we can't give you any partial marks. Important: If you get the correct answer but show none or almost none of the steps that you went through to get the answer -- in other words, if we cannot tell that you did the work to get the answer -- we will give you only 50 % of the full marks.


Laptops can be used in class to keep up with the slides that I show. All slides will be posted well in advance of the lectures. If you want to make notes using your laptop, this is OK. Alternatively, you may want to print out the slides in advance and take notes on the printouts. Either way, you will find that you need to take some notes but not a lot of notes.

During classes, please do not use laptops for web browsing that is not related to the course.

Cell phone use is not allowed, please. NO TEXTING DURING CLASSES.


Information on astronomy courses and on Departmental rules are posted in the Astronomy Department's Memo to Undergraduate Astronomy Students Copies are handed out on the first day of classes.


The University's deadlines and rules regarding dropping the course will be strictly enforced. I will assume that you know the deadlines and the rules. Deadlines are listed in the University's Calendar for Fall 2016 - Spring 2017.

 1. Adds/Drops before the 12th class day: During the first four class days, students may add or drop courses online. The 2017 Spring 4th class day is January 20. During days five through twelve, students may drop a course online but must go to the department offering the course to seek permission to add a course. Be advised that some departments do not allow adds/drops after the fourth class day. Students who wish to add a class after the twelfth class day will be required to see a counselor in the Student Division of the Dean's Office and provide justification for the proposed change. The 2017 Spring add/drop day (12th class day) is February 1.

 2. Dropping a course during the open Q-drop period: The 2017 Q drop period ends on April 3. A student who wants to drop a course can ask the instructor to complete a drop form that assigns a Q or an F. The symbol Q indicates an average of C or better at the time of the drop, or that no grade has yet been assigned, or that due to the student's performance and the nature of the course, no academic penalty is in order, or that for documented non-academic reasons, no academic penalty is in order. Again, the 2017 Spring Q-drop deadline is April 3.

I never refuse a request to Q-drop this course.

 3. The deadline for dropping a course or for changing to credit/no credit or for withdrawing from the University for urgent nonacademic reasons is April 3, 2017.

 4. Courses taken on a pass/fail basis:  The University defines a D- as a passing grade for undergraduate students. The instructor is obliged to assign a grade of CR (Credit) for a student registered on a pass/fail basis who has a D- or better in the course. It is important that the roster indicate the student is registered for the course on a pass/fail basis. Otherwise, a letter grade must be assigned. There is a time limit for students to change courses from a grade basis to pass/fail basis and vice versa. It is the same as the final deadline for drop/withdrawal for academic reasons. After that deadline, students should see a Counselor in the Student Division of the Dean's Office. Students are allowed to change the status of any given course only one time during the pass/fail time period.

John Kormendy's Home Page

University of Texas Astronomy Home Page

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