WELCOME TO ASTRO 100H - 01 (53373)

Spring 2014Exploring the Universe

TT 1:00pm – 2:15pmElm 210

Professor: Dr. Mauro GiavaliscoTA: Mr. Shawn Roberts

Textbook: The Cosmic Perspective, Fifth Edition

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

Contact Information

• Dr. Mauro Giavalisco: – Room 520 LGRT; phone: 413-545-4767– Office Hours: M/W 2:00 – 3:00, or by appointment

– Email: mauro@astro.umass.edu

• Mr. Shawn Roberts– Room 517/M LGRT– Office Hours: by appointment– Email: srrobert@astro.umass.edu

Philosophy of the Course. I

• This course aims at teaching the fundaments of the physical mechanisms that govern the formation and evolution of stars and galaxies. It will also cover elements of cosmology.

• The goal is to introduce you to study, in a quantitative way, the physics of stars and galaxies, as well as the evolution of the cosmo.

• The highlight here is on quantitative. Although we will limit the use of math to algebra and trigonometry, this course is substantially different from the ASTRO 100 level, because it treats the subject in a more quantitative way.

• You will use mathematical formalism to understand the subject and to solve problems

• Although Physics is not a prerequisit, you are requested to be proficient in the use of physical units, and to understand physical dimensions and simple dimension analysis.

Format of the Course

• Course material will be covered in two weekly lessons (TT); readings from the text; homeworks.

• 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.

– (there are stupid answers, however, although this is mostly my problem).

• Not everything from the 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 think like a scientist, quantitatively, 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. I

• Attendance: the single most important element to ensure success in this course

• Reading: assignments from the textbook are given in class and in the course Web site; they are required

• In-Class Exams: there will be 1 in-class, 1-hour exams (multiple choice), each worth 20% of the final grade, for a total of 40%. Anything discussed in the class or in the reading up to the time when the exam is taken will be subject for questions

• Final Exam: it is worth 20%. Anything discussed in the class or in the reading may appear in the final exam.– Makeup exams: will be allowed only for documented medical or family emergencies, or by

prior arrangements in case of conflict schedule.

• Homework: there will be 10 homework assignments, approximately one each week. Each homework is assigned a few days prior its due date, depending on difficulty. Each is worth 4%, for a total of 40%, of the final grade. – Late assignments: will receive half credit

• Extra credit: advanced study material for extra credit, up to 10 points. Tested by WRITTEN ESSAY and ORAL EXAM. They are VERY DIFFICULT!– A bit of an advice: do not even think to use the Extra Credit to make up for a

mediocre or poor course. You will be positively disappointed. • 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 (hoping in the Extra Credit for some help)

• 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. Practice good planning and diligence.

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: 40% (20% each)– 1 Final exam: 20%– 10 Homeworks: 40% (4% each)– Extra credit material (facultative): up to 10%

Course Requirements.III

• MATH: it is just a tool, not a goal in itself.• DO NOT BE SCARED by math. If you have problem, talk to us. In virtually all cases we will solve your problems.

• MATH should not be an impediment toward understanding the subject of astronomy.

• Talk to us, we will help you to solve your math problems

• DO NOT GET STUCK because of math. There is no reason for that.

• HOWEVER, science majors MUST be proficient in math• A modicus of Calculus I is a requirement for this course.

• Mathematical rigor IS A REQUIREMENT for this class.• So, do not get put down by math, but do not get lenient either.

• The best way is: stay proficient day after day, and everything will be OK

About Homework• Homework are crucial to understanding the course material• Homework are NOT multiple-choice tests; they are problems

that are answered with some reasoning and calculations.• Even if you get some math wrong, you can get credit,

partial or even full, if you demonstrate understanding of the physics– WRITE DOWN YOU REASONING as clearly as possible!

• Homework carry 40% of the final grade. That is a lot! Be diligent with your homework.

• Each homework is assigned a few days prior its due date, depending on its difficulty level.

• Although each one of you is responsible for her/his own assignment, discussing with other students and working together is great!

• First Homework (HW1) will be assigned on Thursday, Jan 23, and will accessible by clicking the appropriate link in the Course main Web page. Due IN CLASS on Tuesday, Tuesday 28

About Exams• Exams are all in-class events

– Exams last 1 hr 10 min– Final Exam is 2 hr

• They are multiple-choice tests, and are “open book”, “open notes”.– You might think this is good news. It is not, if you do not understand what you are doing. Furiously browsing books, notes or Wikipedia 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 physics.– Again: when in doubt, write down your reasoning.

• Student-to-student exchange of information during 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 shall 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 keyword

• Each student will give Dr. Giavalisco a keyword of his/her own choice (just come up with something)– Any alpha-numeric sequence, up to 10-character long, will work

– Write it down on a piece of paper, together with your student ID; remember to keep a copy

• To protect your privacy, NO names (own, parents’, friends’, S.O.’s), dates of birth, SSN, driver’s license number, etc.

GRADES CURVING

• 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%)

• DO NOT COUNT ON IT TO PASS THE COURSE!!!

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.

– 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.

• Concepts are new, anti-intuitive and hard to grasp initially.– Dr. Giavalisco will focus on explaining the physics behind new concepts. 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, helping the students develop a physical insight of the various concepts presented during the course. Make sure you come to class and you understand new things.

PED policy

• Cell phones and other Personal Electronic Devices (PEDs): absolutely no PEDs during class.

• PEDs *must* be turned off prior to class entrance

• PED policy will be strictly enforced.

Syllabus (on the Web)• Cosmic Cartography. The electromagnetic radiation

(Light) – A Brief Description of the Universe– Celestial coordinates, flux and magnitudes– Light, telescopes and astronomical exploration

• Gravity, Relativity and Quantum Physics– The physics of gravity– Special and General Relativity– Elements of Quantum Physics

• The stars– The physics of Stars– Stellar Evolution– Stellar Remanants

• Galaxies and Cosmology– The Milky Way– External Galaxies– Galaxy Formation and evolution– Cosmology

The Textbook

The book will be available in the textbook annex by Wednesday, possibly earlier.

It is more advanced than other ASTRO 100 books

I will heavily use the sections named “Mathematical Insight”

Physical Dimensions

• Equations linking physical quantities have dimensions. Eg.:– s = ½ a t2 + v t + s0

– this is the equation of accelerated motion• s is distance, and has the dimension of length• t is elapsed time, has the dimension of time• a is acceleration, has the dimension of length/time2

• Numbers expressing dimensional quantities have units used to measure them.

• Eg.: v = 132 m/s; E = 1019 Joule; g = 9.81 m/s2

– Use units diligently– In this class, a unit mistake is much more severe than a math one

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)

Basic Notions. I• 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 nations (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

• Imagine the Solar system. Its elements are comets, asteroids, planets and satellites, and one star.– Size of planet (Earth): ~12,756 (1.2756x10+4) km ~ 107 m– Distance between star (Sun) and planets (Earth): ~1.5x10+8 km (1.5x10+11 m)• This is also called the Astronomical Unit, AU

– 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 (but also black holes, gas, dust)– Size of a star (Sun): ~1.4x10+11 cm– Distance between stars: ~10+20 cm

• The distance is 9 orders of magnitude larger than the size. If one star is 10-3 m (a poppy seed), the next star is found 106 m = 103 km away

– Time to travel between one star to the next (@ speed of light): ~3x10+8 sec ~ 10 yr (1 yr~3.154x10+7 s)

Basic Notions. III

• 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)

.

At the equator roation speed is: v ~ C/TC ~ 44,000 kmT = 24 hrV ~ 1,800 km/h

At the pole v is v=0 km/hr

We live on Earth, a planet which orbits around a star we call the Sun. Takes 1 year for one round.

Note the tilt between the ecliptic and Earth’s rotation axis

Ecliptic

Speed along the orbit: v ~ 2π x 1.5x108 / 365x86400) km/sec = 30 km/sec

The roation causes night and day. The tilt causes the seasons

170,000 ly

1 ly = 3x105 km/s x (365x86400) = 9.5x1012 km = 9.5x1017 cm

52 feet across

1 mile across

= 6000 feet

=1.6 km

160 kilometers across

1 mile = 1.61 kilometers

Infrared photo

12,756 km

1,600,000 km

=1.6 x 106 km

Moon

1.6x108 km =1.6x1011m1AU = 1.5x1011 m

AU is a distance unit

1.6 x 1010 km, or a trillion (1012) times wider than the first picture! 32 AU

100 AU

10,000 AU

Stars are so far apart from each other!If the Sun is a golf ball in NYC, the nearest star is a golf ball in Chicago!!!

106 AU = 17 ly

1 ly =63,000 AU = 1013 km

1700 ly

170,000 ly

1.7 x 107 ly

The local group of galaxies

1.7 x 109 ly

Basic classes of celestial objects:

Comets and Asteriods

Planets Earth as one

Stars Sun as one

Galaxies Milky Way as one

Their sizes, in a comparative way

Comets and Asteroids: 10-100 km dust grain

Earth: 104 km poppy seed

Sun: 106 km grape fruit

Milky Way 1018 km Earth-Sun distance

Universe 1023 km 100,000 Earth-Sun distance

A Sense of Space

1.The Sun would hold 1.3 million Earths.

i.e. the radius of the Sun is about 100 times

that of the Earth.

2. There are ~100 billion "Suns" in a galaxy like our own Milky Way Galaxy.

3.Astronomers can see billions of

galaxies.

A Sense of Time

If we were to compress the time since the Big Bang into one year, and make the time of the Big Bang January 1, The Earth was formed in mid-September. The mammals appeared on December 26. All human prehistory (from the first known stone tools) and history have occurred in the last ½ hour of New Year's Eve.All of human history is but a fleeting instant on the cosmic timescale.

The Universe

• Universe: everything that existsCosmology addresses the grandest issues:

• How "big" is the Universe?• Does it have an "edge"?• Does it have a shape? What is it?• What is its large-scale structure?• How did it start?• How old is it?• How long will it live?

Our investigation of the universe has become quite sophisticated…Here is the NASA/ESA Hubble Space Telescope (HST)

The COSMIC EXPANSION:Hubble’s Discovery

• In the 1920s, Edwin Hubble used the distance ladder (based on Cepheid variable stars) to measure the distances of about 50 nearby galaxies.

• This work proved that the Andromeda galaxy was not a part of the Milky Way.

• Hubble and his staff then measured the redshifts of the galaxies. They were shocked with what they found.

Hubble's Law

Hubble's DataModern Data

V = H0D

The further a galaxy is away, the faster it’s moving away from us. The Universe Must Be Expanding

Ho = 71 km/s / Mpc.

Distance to a galaxy

The receding velocity causes the redshift of spectral lines, which can be used to estimate distances to distant galaxies that follow the Hubble's law:

D = V/H0.

e.g., for a galaxy with V =7100 km/s, D=100 Mpc

But this is only an estimate on large scales.

V = H0D

Ho = 71 km/s / Mpc.

With the Distance: Charting the

distribution of Galaxies in the

Universe

On average, the universe looks the same in every direction: :ISOTROPYOn average, the universe looks the same in every place: HOMOGENEITY

ISOTROPY + HOMOGENEITY: COSMOLOGICAL PRINCIPLEThe universe looks the same to every observer, no matter where the observer is locatedThere are no special locations in the universe, no edge, no center.

Hubble Law and the Big Bang

The universe is expanding, as if it began in a huge explosion! A big bang!H0 gives us an estimate of the universe's age since this explosion: t =D/V = 1/H0

= 14 Billion years. (1 Mpc =3x1019 km/s; 1 Billion years = 3 x 1016 s)

V = H0D

Ho = 71 km/s / Mpc.

If H0 were bigger (smaller) the age of the universe would be younger (older)

But it is not really an explosion.

It is that the universe was born expanding.

This expansion happens everywhere in thesame way

Every observer sees the same thing

There is no center

The big bang takes place everywhere!

The big bang is still going on!

The space and time was created with the big bang and is changing!

How big is the universe?

If the Universe is infinite, and there is some probability that life happens by chance, how many Astro114 classes, indistinguishable from this one, are currently in session?

just the one we’re currently in

less than 1000

more than 1000 but less than 1 billion

an infinite number

In an infinite Universe, anything that can happen does happen - an infinite number of times.

Does the universe have an edge?

Universe has no edge and no center!

The Universe is a time machine

The Milky Way

The further you look, the younger

they are!

Travel time of light between galaxies is large: ~millions to billions light years

The time machine

• The speed of light is finite:300,000 km/s• It takes time for light to move through space

• E.g. it takes 8 min to come from Sun, and ~2,5 million years to come from Andromeda

• When light reaches us, it shows us how those sources were at the time it left them

• Hence: the further we see in space, the further we see in time

Facts to ponder about the Universe

• It has been expanding for about 14 billion years – the rate of expansion depends on the amount of matter in the Universe.

• Telescopes are time machines and can “see” back to less than 1 billion years after the Big Bang. Structure has formed over time and over a large range of scales (people to clusters of galaxies).

• What next?

Age of the universe at this time = 300,000 years

Does it matter which galaxy you are in?

Does it depend on which direction you

look?