Exploring The Universe - PDF Free Download

WELCOME TO ASTRO 100 Spring 2019 Exploring The Universe http://courses.umass.edu/astron100-nsk Tu/Th 10:00p 11:15p Hasbrouck 20 Professor: Dr. Neal Katz TA: Ms. Yvonne Ban Textbook: Stars and Galaxies, Ninth Edition, Michael A. Seeds

Image of the deep space, up to ~1/2 billion years after the Big Bang, taken with the Hubble Space Telescope

Contact Information Prof Neal Katz: Room LGRT 532; phone: 413-545-2085 Office Hours: Tu/Th 11:30 12:30, or by appointment Email: nsk@astro.umass.edu Ms. Yvonne Ban Room 532a Office Hours: W 11:00-12:00, or by appointment Email: yiwenban@umass.edu

Philosophy of the Course This course will lead you through a journey of about 14 billion years, from the present back to the beginning of time. The goal is to give you an idea of where we happen to exist, introduce you to the most fundamental aspects of physics, from the four forces to the very essence of space and time. At the same time, the course will illustrate the methodology of science and scientific investigation, and the power of innovation and of creative thinking. Size does not matter: we are relatively small, but we do understand an amazing amount about the universe and the physical world. We are able to formulate theories, make predictions, and use them to validate or refute the theories: this is the fundamental methodology of the scientific method. Follow us, and we will show you how and what.

Why Bother with Astronomy? This course will cover larger and smaller topics -- measured by mass, size, age -- you name it! -- than any other class you will ever take. The concepts are not really hard to grasp. Logic, imagination and curiosity are really all that is required. However, these concepts are often new to students, especially non-science majors. It is important to think about them and to try to understand them through reasoning and mental modeling. I will attempt to guide you through this process and help you develop an intuitive understanding. More importantly, we live in a complex society where science and quantitative reasoning play an ever-increasing role. It is crucial that we understand how science and scientists actually work, understand the power and limitations of scientific investigation, and learn how think logically and quantitatively. Even more important, creativity and imaginative thinking are becoming essential to succeed in all aspects of today s life. This is what studying astronomy and physics is all about: curiosity, creativity, imagination. Perhaps this course will spark a life-long interest in science; perhaps not. In any case, the thought processes and reasoning skills you develop this semester should stand you in good stead in situations far surpassing this single undergraduate course.

Format of the Course Course material will be covered in two weekly lessons (Tu/Th); readings from the text; homework. Ample opportunity for interactions: ASK QUESTIONS, in class and during office hours. REMEMBER: there are no stupid questions, except one: the only stupid question is the one you never dared to ask. Not everything from the assigned reading will be covered in class; however, we cover most of it, especially the most difficult parts. Important: you are responsible for all the material in the syllabus. Our goal is to teach you to think like a scientist, analytically and logically. Often answers to exam questions will not be found as a single fact, either in the reading or in the lecture notes, but will require you to think and put one or more facts together in a logical way.

Course Requirements.I Attendance: the single most important element to ensure success in this course. Reading: assignments in the text are given in class and on the course Web site; they are required. Quizzes: there will be 7 quizzes throughout the semester. Only your six highest quizzes will count towards your final grade (you can drop the lowest scoring one), each one worth 2.5%, for a total of 15% of the final grade. Quizzes are identical to exams, but much shorter in length (10-15 min). Exams: there will be 3, 1-hour exams (multiple choice), each worth 15% of the final grade, and one final exam worth 20%. Anything discussed in class or in the readings may appear in exams. Makeup exams: will be allowed only for documented medical or family emergencies, or by prior arrangements. Homework: there will be 8 homeworks, worth 2.5% each, for a total of 20% of the class grade. Extra credit: there is no extra credit. Late assignments: will receive half credit. Academic honesty: expected of all scientists, and science students.

About late assignments Unless a very valid reason is DEMONSTRATED (i.e. creative excuses REALLY do not work), any late assignment will receive ½ credit. We are very strict with this rule. Experience has shown us that students are often late with assignments at the beginning of the course, thinking that they can make it up later. THIS IS A BIG MISTAKE. Do not fall into this trap. Late assignments are the easiest way to end the class with a C or a D (or worse, fail it!). Avoid being late as much as you can.

Grades: will be assigned on a modified straight scale. Scores will be adjusted upward if the exam is too hard. Guaranteed minimum grade: A: 93% C+: 77% A-: 90% C: 73% B+: 87% C-: 70% B: 83% D+:67% B-: 80% D:60% Totals components of Class Grade 6 quizzes: 15% 3 1-hr exams: 45% 1 Final exam: 20% 8 Homeworks: 20% Total Grade Course Requirements.II Class Grade: 75% Lab Grade: 25%

About Homeworks Homeworks are crucial to understanding the course material. Homeworks are NOT multiple-choice tests; they are problems that can be answered with a very short answer. Homeworks carry 20% of the final grade. That is a lot! Be diligent with your homeworks. Students are encouraged to do homeworks in study groups. Discussing with other students and working together is a great way to learn. The first Homework (HW1) is accessible by clicking the appropriate link on the Course main Web page. Due IN CLASS on Thursday, January 24.

About Quizzes and Exams Quizzes and Exams are all in-class events. They are very similar, and differ only in length. Exams are longer and last up to 75 min (Final Exam is 2 hr). Quizzes are shorter and last 10-15 min. The exams will be given on an optional pyramid basis. You may take the exam twice: once in class for 75% of your grade and once at home using your book and notes for 25% of the grade. It is optional and you can choose not to take it home and have the in class grade count 100%. The Final is in class only. Inappropriate behavior (i.e. cheating) will lead to immediate disqualification of the Quiz or Exam (i.e. your grade will be ZERO).

About checking grades Grades will be posted on the Web (see link on the course main page) To protect the privacy of each student, however, students names will NOT APPEAR with grades. Student IDs are not allowed either, as per University policy. Instead of names, each student will be identified by a unique, secret password. Each student that wants access to their grades will send Ms. Ban a password of his/her own choice (just come up with something). Email it to Ms. Ban together with your name and student ID; remember to keep a copy for yourself. The password MUST be alpha-numeric strings 10-characters long. NO names (own, parents, friends, S.O. s), dates of birth, SSN, driver s license number, etc., please!

PCD policy Cell phones and other Personal Communication Devices (PCDs): absolutely do not use PCDs during class. PCDs *must* be turned off prior to entering class. The idea is that: One should not disturb the class. One is in the class to pay attention.

Syllabus (on the Web) Exploring the Sky The solar system and planetary motions The physics of gravity Light, atoms, and spectra The stars The properties of stars The physics of stars Life cycles of stars The Universe The Milky Way External Galaxies Galaxy Formation and evolution Cosmology http://courses.umass.edu/astron100-nsk

Assigned Reading Chapter 1, Chapter 2.1,2.2, 2.3; Magnitude and Flux excluded. Appendix A, p. A3-A5

Scales of the Universe Goals to refresh and use scientific notation to remember how to convert units! to see the levels of structure in the Universe to comprehend the vastness of scales in the Universe

How big is astronomy? Two ways to express very large (or very small) numbers: Define new units, e.g. AU (astronomical unit): distance from the earth to the sun LY (light year): the distance that light travels in a year Use powers of 10 and scientific notation Why powers of 10? Babylonians used powers of 60!

Names for powers of 10 0.01 = 10-2 centi (c) 0.001 = 10-3 milli (m) 0.000001 = 10-6 micro ( ) 0.000000001 = 10-9 nano (n) 10 = 10 +1 deca 1,000 = 10 +3 kilo (K) 1,000,000 = 10 +6 mega (M) 1,000,000,000 = 10 +9 giga (G)

0.0000206265 = 2.06265 x 10-5

Multiplying and dividing factors of 10 is easy! x 10 a y 10 b = x y 10 a b Similarly, x 10 a y 10 b = x y 10a b For Example: 6 10 8 2 10 4 =3 10 4

Examples 6300 x 400= (6.3 x 10 3 ) x (4.0 x 10 2 )= (6.3 x 4.0) x (10 3 x 10 2 )= 25.2 x 10 5 = 2.52 x 10 1 x 10 5 = 2.52 x 10 6 400/0.2= (4 x 10 2 )/(2 x 10-1 )= (4/2) x (10 2 /10-1 )= 2 x 10 2-(-1) = 2 x 10 3

Survey Question In 2016, the budget deficit was estimated to be about $500 billion. If there are roughly 100 million households in the U.S., how much debt would each household acquire if the deficit were split evenly among them? 1) $50 2) $500 3) $5,000 4) $50,000

Understanding scale is easy! 10 6 + 3x10 6 = 4x10 6 1,000,000 + 3,000,000 4,000,000 But 10 8 +10 4 10 8 100,000,000 + 10,000 100,010,000

Survey Question For which of the following are x, y, and z most nearly the same? 1) 2) x=10 9 10 9, y=10 5 2 10 4, z=3 10 11 /10 2 x=10 2 10 6, y=10 2 2 10 8, z=10 11 /10 9 3) x=10 3 10 6, y= 5 104 10 2 10 2, z=1011 /10 11

Units Conversion First of all Units are good things! You can say the distance to Boston in miles (or km) instead of inches (or cm)! Translating to useful units is a very handy skill. The key to changing units is remembering to replace a unit by something equivalent.

Converting Units How many quarters are there in 1000 dollars? 1000 dollars= 1000 x 1 dollar = 1000 x 4 quarters = 4000 quarters Question: How many cm are there in 3 km? 3 km = 3 x 1km = 3 x 1000 m= 3000 m = 3000 x 1m = 3000 x 100 cm = 300000 cm

Speed = distance/time = m/s The speed of light: c = 3x10 8 m/s. c is Constant Finite The fastest speed there is in the Universe Whenever you see "light-(time)", that means we are talking about distance, not time.

Light traveling time = distance Car-traveling time as distance: Boston is about 1.5 hours away (assuming the speed of a car is 60 mph). Destination Distance (km) Light Travel time London 6,000 0.02 s Moon 385,000 1.3 s Sun 1.5 x 10 8 500 s (8.3 min) Jupiter 7.8 x 10 8 43 min Nearest Star 4 x 10 13 4.3 years Most Distant Galaxy 1.4 x 10 23 14 billion years Whenever you see "light-(time)", that means we are talking about distance, not time.

Examples 1 yr = 3.16 x 10 7 s (Earth revolves around the Sun once). 1 ly = (3 x 10 5 km/s) x 3.16 x 10 7 s = 9.45 x 10 12 km 10 thousand billion km!

The Size of The Universe Time = Distance / Speed Imagine a neighborhood. Its elements are blocks. Block size: ~100 meters. Inter block distance: 200 meters. Time to go from one block to another (walking speed 5 km/hr): ~ minutes. Imagine a country. Its elements are cities. City size: ~ 30 km. Inter-city distance: ~10 2 km. Time to go from one city to another (driving speed, 100 km/hr): ~ few hours. Imagine the Earth. Its elements are countries. Country size: ~2,000 (~2x10 3 ) km. Inter-country distance: several 10 3 km. Time to go from one country to another (jet speed, 900 km/hr): ~ several hours.

The Size of the Universe Imagine the Solar system. Its elements are planets (asteroids and comets are much smaller). Size of planet (Earth): ~12,756 (1.2756x10 4 ) km. Distance between planets: ~1.5x10 8 km (1.5x10 11 m). Time to travel from one planet to another (speed of light, c=3.8x10 5 km/s or 3.8x10 8 m/s or 3.8x10 10 cm/s): ~0.5x10 3 s (about 8 min). Imagine the galaxy. Its elements are stars. Size of a star (Sun): ~1.4x10 11 cm. Distance between stars: ~10 13 km. Time to travel between one star to the next (speed of light): ~3x10 5 km/sec ~ 10 yr (1 yr~3.154x10 7 s).

The Size of The Universe Imagine the Universe. Its elements are galaxies. Size of a galaxy (The Milky Way): ~9.3x10 22 cm. Distance between galaxies: ~3x10 24 cm. Time to travel between one galaxy to the next (speed of light): ~1x10 14 sec ~ 3x10 6 yr. The Universe is big (compared to us). Light is pathetically slow for its size (and we can t even go that fast ).