A100H Exploring the Universe: Introduction. Martin D. Weinberg UMass Astronomy

A100H Exploring the Universe: Introduction Martin D. Weinberg UMass Astronomy astron100h-mdw@umass.edu January 19, 2016 Lec 01 01/19/16 slide 1

What is Astronomy? Story of our understanding of the Universe By the end of the course, we will have traveled through the solar system, the Galaxy, clusters of galaxies to the beginning of the Universe. Objectives Organization of the Universe Principal components that create this organization Scientific method: how we try overcome human perceptual limitations to figure this out Lec 01 01/19/16 slide 2

Earth in the Universe Lec 01 01/19/16 slide 3

Earth in the Universe 10 4 km Lec 01 01/19/16 slide 3

Earth in the Universe 10 10 km 10 4 km Lec 01 01/19/16 slide 3

Earth in the Universe 10 18 km 10 10 km 10 4 km Lec 01 01/19/16 slide 3

Earth in the Universe 3 10 19 km 10 18 km 10 10 km 10 4 km Lec 01 01/19/16 slide 3

Earth in the Universe 10 21 km 3 10 19 km 10 18 km 10 10 km 10 4 km Lec 01 01/19/16 slide 3

Scale of the Universe Sun = basketball Earth = marble at a few hundred feet Nearest star = about 10000 miles away (Tokyo) Center of the Milky Way = 10000 times the nearest star or 100,000,000 miles away Nearest Galaxy = 1000 times distance to center of Milky Way 100,000,000,000 miles away Lec 01 01/19/16 slide 4

Human biases Cosmic length scales very large compared to human size Cosmic time scales very long compared to human lifetime Cosmic events at many wavelengths humans have limited sensitivity to the electromagnetic spectrum Lec 01 01/19/16 slide 5

Looking into the past What was the Universe like in the past? Destination Light travel time Moon 1 second Sun 8 minutes Sirius 8 years Andromeda Galaxy 2.5 million years Lec 01 01/19/16 slide 6

Looking into the past What was the Universe like in the past? Destination Moon Sun Sirius Andromeda Galaxy Light travel time 1 second 8 minutes 8 years 2.5 million years Observing at large distances is looking back in time!! Lec 01 01/19/16 slide 6

Looking into the past What was the Universe like in the past? Destination Light travel time Moon 1 second Sun 8 minutes Sirius 8 years Andromeda Galaxy 2.5 million years This is known as the Space-time continuum Lec 01 01/19/16 slide 6

The distance light can travel in one year About 10 trillion km (6 trillion miles) Lec 01 01/19/16 slide 7

The distance light can travel in one year About 10 trillion km (6 trillion miles) At great distances we see objects as they were when the Universe was much younger Lec 01 01/19/16 slide 7

The distance light can travel in one year About 10 trillion km (6 trillion miles) At great distances we see objects as they were when the Universe was much younger Question: can we see the entire Universe? Lec 01 01/19/16 slide 7

Three encompassing topics Motions, Light and Gravity Stars Galaxies & Cosmology Lec 01 01/19/16 slide 8

Three encompassing topics Motions, Light and Gravity Stars Galaxies & Cosmology Textbook: The Cosmic Perspective: Stars, Galaxies and Cosmology, 7e, by Bennett et al. Lec 01 01/19/16 slide 8

Three encompassing topics Motions, Light and Gravity Stars Galaxies & Cosmology Textbook: The Cosmic Perspective: Stars, Galaxies and Cosmology, 7e, by Bennett et al. Attendance is optional, but you are responsible for topics covered in class whether you attend or not. Lec 01 01/19/16 slide 8

Reading: Assignments in the text for each class will be given in preceding class and are required. The relevant chapters are also listed in the Syllabus by subject. You should expect to spend about 3 hours out of class for every one hour of class time. Effort = Final Grade Read: Chap 1 01/19/16 slide 9

Exams: Two in-class one-hour exams and a final exam. The exams will be multiple choice and short answer. 65% of total grade. The exam dates are in the syllabus. They will only change if the University is closed (e.g. snow day). In that case, the exam will be held at the next class meeting. Format: combination of multiple choice and short answer questions. Makeup exam policy: Following the University guidelines, makeup exams will be given only for documented medical or family emergencies or by prior arrangement. Read: Chap 1 01/19/16 slide 10

Homework: There will be (roughly) weekly homework assignments worth 25% of the total lecture score. We will using www.masteringastronomy.com, an online assignment system. Read: Chap 1 01/19/16 slide 11

Homework: There will be (roughly) weekly homework assignments worth 25% of the total lecture score. We will using www.masteringastronomy.com, an online assignment system. Special-topic reports: Choose three topics of interest to you (approx. 1000 words). Due by end of February (1), end of March (2) and end of April (3). Worth 10% of the total score. See web site for suggested list of topics. Confirm others with me. Read: Chap 1 01/19/16 slide 11

Extra credit: At the end of each class, you may pass in a sheet of paper with your name, UMass ID and 1. Brief description of an idea or topic from the day that you found particular interesting 2. Your top question from the day s class Over the entire semester, this is worth up to 5% to your final score. Some of the homework assignments will have additional questions that count for extra credit. There are no other forms of extra credit. Read: Chap 1 01/19/16 slide 12

will be assigned on a modified straight scale. Scores will be adjusted upward if the exam is too hard. 92.5% A 90% A- 87.5% B+ 82.5% B 80% B- 77.5% C+ 72.5% C 70% C 67.5% D+ 60% D 3 exams 65% Online homework 25% In-class feedback 5% Topical reports 10% Academic Honesty is expected of all scientists, and also of all students of science. Read: Chap 1 01/19/16 slide 13

Interactive, online homework and study system (see your handout) You must register using the access packet that comes with your textbook Buying a used book is perfectly OK; need to purchase access on line for $61.00 Can purchase e-text and for $96 Read: Chap 1 01/19/16 slide 14

Read: Chap 1 01/19/16 slide 14

: grading The assignments untimed. You may stop in the middle, go back later, etc. The system offers you hints, if you want them. Not using hints is worth 2% bonus credit. If you give an incorrect response, in many cases, you will get some extra help from the system and you can try again. However, every time you answer incorrectly, you lose 20% of the available credit for that problem. Assignments submitted before the due date, of course, get full credit. For every day an assignment is late, you lose 3.5%. So after approximately two weeks, you will have lost 50%. Assignments that are more than two weeks late receive at most 1/2 credit. Read: Chap 1 01/19/16 slide 15

: assignments Practice assignment available (DO THIS FIRST) Check your computer/browser/plugin installation by testing all aspects of Get used to style First real assignment available Physical scales Due next Tue Read: Chap 1 01/19/16 slide 16

Scientific Notation 10 21 km 3 10 19 km 10 18 km 10 10 km 10 4 km Read: Chap 1 01/19/16 slide 17

Scientific Notation The numbers encountered in this class are astronomical: The nearest star is 41,000,000,000,000 kilometers away The mass of the sun is 2,000,000,000,000,000,000,000,000,000,000,000 grams Scientists have devised a more compact notation for dealing with such numbers called scientific notation. Read: Chap 1 01/19/16 slide 18

Scientific Notation 41,000,000,000,000 kilometers 2,000,000,000,000,000,000,000,000,000,000,000 grams There are really only two important parts to each of the numbers: 1. The leading digits which establish the precision of the number itself 2. The number of digits which sets the size or magnitude of the number In Scientific notation: 4.1 10 13 and 2.0 10 33 Read: Chap 1 01/19/16 slide 19

Scientific Notation The is, as it appears, a multiplication: 10 2 = 10 10 = 100 10 3 = 10 10 10 = 1,000 10 4 = 10 10 10 10 = 10,000 10 5 = 10 10 10 10 10 = 100,000 10 6 = 10 10 10 10 10 10 = 1,000,000 so 4.5 10 4 = 4.5 10 10 10 10 = 45,000. Read: Chap 1 01/19/16 slide 20

Scientific Notation Counting zeros and moving the decimal place is a convenient way of carrying out the multiplication by powers of ten Example: Want: 10 3 10 5 10 3 10 5 = 10 10 10 10 10 10 10 10 = 10 8 The result of that long string of multiplication is that we add the exponents of the 10 s: 3 + 5 = 8 Read: Chap 1 01/19/16 slide 21

Scientific Notation Addition a bit more tricky: 10 3 +10 5 = 10 10 10 + 10 10 10 10 10 = 1.01 10 5 Read: Chap 1 01/19/16 slide 22

Scientific Notation Addition a bit more tricky: 10 3 +10 5 = 10 10 10 + 10 10 10 10 10 = 1.01 10 5 or 1,000+100,000 = 101,000 = 1.01 10 5 Read: Chap 1 01/19/16 slide 22

Scientific Notation Addition a bit more tricky: 10 3 +10 5 = 10 10 10 + 10 10 10 10 10 = 1.01 10 5 or or 1,000+100,000 = 101,000 = 1.01 10 5 0.01 10 5 +1.0 10 5 = 1.01 10 5 Rule: add the prefix (mantissa) when power of ten (exponent) for the addends is the same Read: Chap 1 01/19/16 slide 22

1 light-year = (speed of light) (1 year) = 300,000 km s 1 year = 300,000 km 1 year s 60 min 1 hour 60 s 1 min 365 days 1 year 24 hr 1 day Read: Chap 1 01/19/16 slide 23

1 light-year = (speed of light) (1 year) = 300,000 km 1 year s = 300,000 km 1 year s 365 days 1 year 60 min 1 hour 60 s 1 min 24 hr 1 day Read: Chap 1 01/19/16 slide 23

1 light-year = (speed of light) (1 year) = 300,000 km 1 year s = 300,000 km 1 year s 365 days 1 year 60 min 1 hour 60 s 1 min = 9,460,000,000,000 km 24 hr 1 day Read: Chap 1 01/19/16 slide 23

1 light-year = (speed of light) (1 year) = 300,000 km 1 year s = 300,000 km 1 year s 365 days 1 year 60 min 1 hour 60 s 1 min = 9,460,000,000,000 km = 9.46 10 12 km 24 hr 1 day Read: Chap 1 01/19/16 slide 23

1 light-year = (speed of light) (1 year) = 300,000 km 1 year s = 300,000 km 1 year s 365 days 1 year 60 min 1 hour 60 s 1 min = 9,460,000,000,000 km = 9.46 10 12 km 10 13 km 24 hr 1 day Read: Chap 1 01/19/16 slide 23

10 15 femto- 10 12 pico- 10 9 nano- 10 6 micro- 10 3 milli- 10 2 centi- 10 1 deci- 10 deka- 10 2 hecto- 10 3 kilo- 10 6 mega- 10 9 giga- 10 12 tera- 10 15 peta- Read: Chap 1 01/19/16 slide 24

Measuring distance Distance in meters (m) Read: Chap 1 01/19/16 slide 25

Energy Source Big Bang 10 68 Radio galaxy 10 55 Supernova 10 46 Sunlight (1 y) 10 34 Volcanic explosion 10 19 H-bomb 10 17 Thunderstorm 10 15 Lightning flash 10 10 Baseball pitch 10 2 Typing (per key) Flea hop Total Energy (J) 10 2 10 7 Read: Chap 1 01/19/16 slide 26

Earth rotates: speed = 0.5 km/s = 1,700 km/hour = 1,000 miles/hour Read: Chap 1 01/19/16 slide 27

Earth rotates: speed = 0.5 km/s = 1,700 km/hour = 1,000 miles/hour Earth orbital speed (solar system) = 30 km/s = 170,000 km/hour = 67,000 miles/hour Read: Chap 1 01/19/16 slide 27

Earth rotates: speed = 0.5 km/s = 1,700 km/hour = 1,000 miles/hour Earth orbital speed (solar system) = 30 km/s = 170,000 km/hour = 67,000 miles/hour Sun s orbital speed (Galaxy) = 200 km/s = 450,000 miles/hour Read: Chap 1 01/19/16 slide 27

Motions in the galaxy Read: Chap 1 01/19/16 slide 28

Read: Chap 1 01/19/16 slide 29

Expanding Universe Discovery by Edwin Hubble in 1929 All galaxies outside of our Local Group are moving away from us The more distant the galaxy, the faster it is moving Nothing special about our location in the Universe Read: Chap 1 01/19/16 slide 30

Read: Chap 1 01/19/16 slide 31

Read: Chap 1 01/19/16 slide 32

Gas (mostly hydrogen) settles in the disk of galaxies This gas fragments into dense knots, forms stars The stars fuse hydrogen into helium and heavier, generating energy The star explodes! Galaxy: a huge island of stars moving around a common center and held together by gravity. Read: Chap 1 01/19/16 slide 33

Gas (mostly hydrogen) settles in the disk of galaxies This gas fragments into dense knots, forms stars The stars fuse hydrogen into helium and heavier, generating energy The star explodes! Nebula: an interstellar cloud of dust and/or gas Read: Chap 1 01/19/16 slide 33

Gas (mostly hydrogen) settles in the disk of galaxies This gas fragments into dense knots, forms stars The stars fuse hydrogen into helium and heavier, generating energy The star explodes! Star: generates heat and light through nuclear fusion Read: Chap 1 01/19/16 slide 33

Gas (mostly hydrogen) settles in the disk of galaxies This gas fragments into dense knots, forms stars The stars fuse hydrogen into helium and heavier, generating energy The star explodes! Supernova: fusion fuel exhausted, the star explodes Read: Chap 1 01/19/16 slide 33

Time for Earth to make one rotation: 1 day Read: Chap 1 01/19/16 slide 34

Time for Earth to make one rotation: 1 day Time for Earth to orbit the Sun: 1 year Read: Chap 1 01/19/16 slide 34

Time for Earth to make one rotation: 1 day Time for Earth to orbit the Sun: 1 year Time for Uranus to orbit the Sun: 84 years Read: Chap 1 01/19/16 slide 34

Time for Earth to make one rotation: 1 day Time for Earth to orbit the Sun: 1 year Time for Uranus to orbit the Sun: 84 years Time for Sun to Orbit the Galaxy: Time = 2π 28,000 light years 200 km/s Read: Chap 1 01/19/16 slide 34

Time for Earth to make one rotation: 1 day Time for Earth to orbit the Sun: 1 year Time for Uranus to orbit the Sun: 84 years Time for Sun to Orbit the Galaxy: Time 2π 28,000 light years = 200 km/s 28,000 light years = 2π 220 km/s 9.46 10 12 km 1 year 1 light year 3.15 10 7 s Read: Chap 1 01/19/16 slide 34

Time for Earth to make one rotation: 1 day Time for Earth to orbit the Sun: 1 year Time for Uranus to orbit the Sun: 84 years Time for Sun to Orbit the Galaxy: Time 2π 28,000 light years = 200 km/s = 2π 28,000 light years 220 km/s 9.46 10 12 km 1 year 1 light year 3.15 10 7 s = 2.4 10 8 year = 240 10 6 year Read: Chap 1 01/19/16 slide 34

Time for Earth to make one rotation: 1 day Time for Earth to orbit the Sun: 1 year Time for Uranus to orbit the Sun: 84 years Time for Sun to Orbit the Galaxy: 240 million years Time for Milky Way to collide with Andromeda Galaxy: 10 billion years Read: Chap 1 01/19/16 slide 34