Exploring The Universe

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WELCOME TO ASTRO 100 – Section 2 (14319) Spring 2017 Exploring The Universe www.astro.umass.edu/~mauro/astro100

  • T/T 1:00pm – 2:15pm
  • Hasbrouck 124
  • Professor: Dr. Mauro Giavalisco
  • TA: Mr. Shuiyao Huang
  • Textbook: Stars and Galaxies, Fifth to Seventh Edition, Michael A. Seeds
  • A 85%-scale mock of the Hubble Space Telescope at the NAS museum, D.C.
  • The recommended textbook

Contact Information

  • Dr. Mauro Giavalisco:
    • Room LGRT-B 520; phone: 413-545-4767
    • Office Hours: M/W 2:00 – 3:00, or by appointment
    • Email: mauro@astro.umass.edu
  • Mr. Shuiyao Huang
    • Room LGRT-C 531; phone: 413-545-3026
    • Office Hours: by appointment
    • Email: shuiyao@astro.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 the 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 lot about the universe and the physical world.
  • We are able to formulate theories, make predictions, and use them to validate or refuse the theories (maybe at a future time, if technology limitations place things beyond our immediate empirical reach): this is the fundamental methodology of the scientific method.
  • Follow us, and we will show you how and what.

What this course is not

  • This is not a seminary class; it is a full 4-credit course, including lecture, mid-terms and home assignments
  • Do not expect a documentary-style class, it is not
  • This is a formal course on astronomy, astrophysics and cosmology at the level for non-science majors

Why Bother with Astronomy and Science in General?

  • Astronomy (astrophysics) is the part of physics that concerns with the birth and evolution of the universe and of cosmic structures (e.g. galaxies, black holes, stars, planets, dark matter, dark energy etc.)
  • This course will cover big 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 try to understand them through reasoning and mental modeling.

Why Bother with Astronomy and Science in General?

  • We live in a complex society where science and quantitative reasoning, innovation play an ever-increasing role.
  • It is crucial that we understand scientific investigation and methodology, their power and limitations; learn to think critically, logically, deductively and quantitatively.
  • 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, thinking out of the box, looking at the big picture, testing our ideas against the empirical world.
  • Perhaps this course will spark a life-long interest in science; perhaps not. In any event, the thought processes and reasoning skills you develop this semester should stand you in good stead in situations far surpassing this single undergraduate 4-credit course.

Scientific Methodology

  • There is no “ultimate truth” (or at least it is not attainable)
  • Theory is not truth: it is a conceptual framework useful to explain the data (i.e. the real world) within the available accuracy
  • The ultimate test of science is explaining and reproducing the real world
  • If a theory cannot explain the data, it is either amended or rejected altogether
  • Good theories are never rejected; they are generalized
  • Science is all about the “real world”

Format of the Course

  • Course material will be covered in two weekly lessons (T/T); readings from the text; homework.
  • Ample opportunity for interactions: ASK QUESTIONS, in class and during office hours.
    • there are no stupid questions, except one:
      • the only stupid question is the one you never dared to ask.
    • (there are stupid answers, however).
  • 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
  • Testing and evaluation consists in two mid-term exams and one final exam
  • Our goal is to teach you think like a scientist, analytically and logically. Answers to homework and 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

  • Attendance: the single most important element to ensure success in this course
  • Reading: assignments in the text are given in class and in the course Web site; they are required
  • Exams: there will be 2, 1-hour exams (multiple choice), each worth 15% of the final grade, for a total of 30%, and one final exam worth 30%. Anything discussed in the class or in the reading 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 essay-type homework, each worth 5%, for a total of 40% of the final grade.
  • 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 grade.
  • 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 up later
  • THIS IS A BIG MISTAKE. Do not fall in this trap. Late assignments are the most effective way to end the class with a C or a D (or, worse, Fail it!)
  • Avoid being late as hard as you can.

Course Requirements.II

  • Grades: will be assigned on a modified straight scale. Scores will be adjusted upward if the exams is too hard
  • Guaranteed minimum grade:
    • A: 92%
    • AB: 87%
    • B: 82%
    • BC: 77%
    • C: 72%
    • CD: 67%
    • D: 60%
  • Totals of components of Final Grade
    • 2 1-hr exams: 30%
    • 1 Final exam: 30%
    • 8 Homeworks: 40% (5% each homework)

Course Requirements.III

  • MATH: it is just a tool, not a goal in itself
  • DO NOT BE SCARED by math. If you have problems, talk to us. In virtually all cases we will solve your problems
  • MATH should not be an impediment toward understanding the subject of astronomy
  • Typically, most people who have problems with math have had a bad imprinting with it
  • Talk to us and we will help you and solve your math problems
  • Again: DO NOT GET STUCK because of math. There is no reason for that
  • Difficulty in this class is with Astronomy, not Math

About Homeworks

  • Homeworks are crucial to understanding the course material
  • Homeworks are NOT multiple-choice tests; they are problems that can be answered in a (very short) essay-type way
  • Even if you get the math wrong, you can get credit, partial or even full, if you demonstrate understanding of the subject
    • WRITE DOWN YOU REASONING as clearly as possible!
  • Homeworks carry 20% of the final grade. That is a lot! Be diligent with your homeworks
  • Students strongly encouraged to do homeworks in study groups
  • Discussing with other students and working together is a great way to learning
  • First Homework (HW1) will be assigned in ~10 days and will accessible by clicking the appropriate link in the Course main Web page.

About Quizzes and Exams

  • Mid-term Exams and Final Exam are all in-class events
  • They are very similar, and differ only in length
    • Exams are longer and last ~1 hr; Final Exam is 2 hr
  • They are all “open book”, “open note”, “open phone, tablet, etc”.
    • You might think this is good news. It is not, if you do not understand what you are doing. Furiously browsing the book or your notes will simply make you waste tons of time, unless you know what you are looking for… 
  • IMPORTANT! Even if you get the wrong answer, you can get partial credit if you give us any indication that you understand the subject.
    • Again: when in doubt, write down your reasoning.
  • Student-to-student exchange of information during Quizzes and Exams is strictly forbidden, however!
  • Inappropriate behavior will lead to immediate disqualification of the 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 privacy of each students, however, students’ names must NOT APPEAR with grades
  • Student IDs do not work either, as per University policy
  • Instead of names, each students will be identified by a unique, secret password
  • Each student will give Dr. Giavalisco a password of his/her own choice (just come up with something)
    • Write it down on apiece of paper, together with your student ID; remember to keep a copy
  • Password MUST be alpha-numeric strings 10-character long
  • NO names (own, parents’, friends’, S.O.’s), dates of birth, SSN, driver’s license number, etc., please!


  • We will curve the final grades
  • This means that if we realize that we have been either too tough or to easy, I will adjust the final grade upward, or downward, to compensate.
  • Typically, the curving process makes grades go upward (by a little, about 3-5%)

About Course Attendance

  • Unless by prior arrangements, students who do not attend the first two classes will be dropped from course
  • If you are not registered and want to, see me after class
  • The biggest mistake a student might make is thinking to pass this course with no attendance. Experience has shown us that this is simply not possible.

Things that bite in this class

  • A lot of information and the pace of the class is fast.
    • Consistent attendance is the single, most important way to mitigate this problem. It is really crucial to come to class every time, participate and ask questions
  • Concepts are new, anti-intuitive and hard to grasp initially.
    • Dr. Giavalisco will focus on explaining new concepts at an intuitive level. However students need to continuously think about them and try to develop their own mental models to explain and make sense of them.
    • The development of your own mental models to make sense of the course material is the key difference between reading and studying
    • Contact Dr. Giavalisco any time you run into problems. If you get stuck, ask for help IMMEDIATELY!
  • Difficult to locate homework answers in the book.
    • Dr. Giavalisco does not read from the book. Rather he explains the material of the course stressing the physical meaning, and helping the students develop an intuitive understanding of the various concepts presented during the course. Make sure you come to class and you understand new things.

PCD policy

  • Cell phones and other Personal Communication Devices (PCDs): absolutely do not use PCDs during class.
  • The idea is that:
    • One cannot disturb the class
    • One is in the class to follow it

Syllabus (on the Web)

  • Exploring the Sky
    • The solar system and planetary motions
    • The physics of gravity
    • Light, telescopes and astronomical exploration
  • The stars
  • The Universe
    • The Milky Way
    • External Galaxies
    • Galaxy Formation and evolution
    • Cosmology
  • Life
    • Nature of life
    • Life in other worlds and possible communications with them

Scientific Notation and Units

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

To understand and accurately describe what we see, we need numbers and units

  • Amherst:
  • UMass is about 1.5 miles from the center;
  • Antonio’s pizza is about 1 pound a slice
  • The town was founded about 200 years ago
  • The Universe:
  • The nearest star is 4 light years away;
  • The mass of a massive black hole is about 108 solar mass (1 solar mass is ~2x1030 Kg)
  • The age of the Universe is about 14 billion (109) years
  • The scales we meet in exploring the Universe are very big, we must learn how to deal with them

How to say big numbers

  • Billion Giga (G) 109
  • Million Mega (M) 106
  • Thousand Kilo (K) 103
  • ...
  • thousandth milli (m) 10-3
  • millionth micro () 10-6
  • billionth nano (n) 10-9

Scientific Notations

  • Metric system standard in science. Refresh your conversions:
    • 1 inch = 2.54 cm; 1 mile = 1,609 m = 1.609 km
    • 1 lb = 454 gr = 0.454 kg; 1 qt = 0.95 liter (l) = 950 cm3
  • 0.1 = 1.0x10-1 deci
  • 0.001 = 1.0x10-3 milli (m)
  • 0.000001 = 1.0x10-6 micro ()
  • 0.000000001 = 1.0x10-9 nano (n)
  • 10 = 1.0x10+1 deca
  • 1,000 = 1.0x10+3 kilo (K)
  • 1,000,000 = 10x10+6 mega (M)
  • 1,000,000,000 = 10x10+9 giga (G)
  • 0.0000206265 = 2.06265 x 10-5

Logarithms. I

  • OK, so 0.00001 = 10-5 and 1,000 = 103
  • All the information is in the exponent, i.e. the “-5” and “3” thinghies
  • The “10” does nothing, it is always the same in all numbers, carries no information
  • Why not just using the “-5” or “3” to represent 0.00001 or 0.001, respectively?
  • Well, that is done, actually: “-5” and “3” are the logarithms of 0.00001 and 1,000
  • It is that simple!!!

Logarithms. II

  • So, the logarithm of 1,000 is 3, and the logarithm of 10,000 is 4.
  • What if my number is neither 1,000 nor 10,000 but something in between, like 5,437.
  • Well, the logarithm of 5,437 will be in between 3 and 4 (it is 3.7353593).
  • You cannot calculated it yourself, you need a calculator
  • But now you know what a logarithm is!

Logarithm. III

  • In fact, you might wonder why you need 10 (called the base) to express a number via its logarithm.
  • In principle, you could use any other number as base.
  • This is true, actually
  • Any number can be expressed as a logarithm relative to some designated “base”.
  • In other words:
  • Number = baselogarithm
  • When base = 10, the logerithm is called the “decimal”
  • Multiplying and dividing factors of 10 is easy!
  • For Example:
  • Similarly,
  • Survey Question
  • Suppose that this year, the budget deficit is 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
  • $500x109 / $100x106 = $5x103 = $5,000

Understanding scale is easy!

  • 1,000,000
  • + 3,000,000
  • 4,000,000
  • 106 + 3x106 = 4x106
  • 100,000,000
  • + 10,000
  • 100,010,000
  • But …

Survey Question

  • For which of the following are x, y, and z most nearly the same?
  • 1)
  • 2)
  • 3)

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= 1000x 1 dollar
  • = 1000x 4 quarters
  • = 4000 quarters
  • How many cm are there in 3 km?
  • 3 km = 3x 1km
  • = 3x 1000 m= 3000 m
  • = 3000x 1m
  • = 3000x 100 cm
  • = 300000 cm
  • How many meters are there in 1 (statute) mile?
  • 1 mile = 1,609 meter = 1.609 km

The speed of light: c = 3x105 km/s.

  • Destination Distance (km) Light Travel time
  • London 6,000 0.02 s
  • Moon 385,000 1.3 s
  • Sun 1.5 x 108 500 s (8.3 min)
  • Jupiter 7.8 x 108 43 min
  • Nearest Star 4 x 1013 4.3 years
  • Most Distant Galaxy 1.4 x 1023 14 billion years
  • Whenever you see "light-(time)", that means we are talking about distance, not time.
  • Light-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)


  • 1 yr = 3.15 x 107 s (Earth revolves around the Sun once)
  • 1 ly = (3 x 105 km/s) x 3.15 x 107 s = 9.45 x 1012 km
  • =10 thousand billion km!

Now… on to scales in the Cosmos...

Basic Notions. I: The Size of The Universe

  • Time = Distance / Speed t = d/v
    • “t” stands for time; “d” stands for distance and “v” stands for speed
  • Imagine a neighborhood. Its elements are blocks
    • Block size: ~100 meter
    • Inter block distance: 200 meter
    • 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 city to another (jet speed, 900 km/hr): ~ several hours

Basic Notions. II: 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=3.079x10+5 km/s or 3.079x10+8 m/s or 3.079x10+10 cm/s): ~0.5x10+3 s (about 8 min).
  • Imagine the galaxy. Its elements are stars and gas
    • 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)

Basic Notions. III: 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)
  • The light is “pathetically” slow for its size (and we can’t even go that fast…)

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