Astronomy 114

Astronomy 114

Introduction

Martin D. Weinberg

weinberg@astro.umass.edu

UMass/Astronomy Department

A114: Lecture 1—29 Jan 2007 Astronomy 114—1/16

Overview (1/4)

What is Astronomy?

Story of our understanding of the Universe

By the end of the course, we will have traveledthrough the solar system, the Galaxy, clusters ofgalaxies to the beginning of the Universe.

Overview (1/4)

What is Astronomy?

Story of our understanding of the Universe

By the end of the course, we will have traveledthrough the solar system, the Galaxy, clusters ofgalaxies to the beginning of the Universe.

Objectives

Organization of the Universe

Principal components that create this organization

Scientific method: how we try overcome humanperceptual limitations to figure this out

Overview (2/4)

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 neareststar or 100,000,000 miles away

Nearest Galaxy = 1000 times distance to center ofMilky Way 100,000,000,000 miles away

Overview (3/4)

Human biases

Cosmic length scales—very large compared tohuman size

Cosmic time scales—very long compared to humanlifetime

Cosmic events at many wavelengths—humans havelimited sensitivity to the electromagnetic spectrum

Overview (4/4)

Three encompassing topics

Motions, Light and Gravity

Galaxies & Cosmology

Overview (4/4)

Text book: Universe by Freedman &Kauffman

Overview (4/4)

My role is to help you understand.Please ask questions!!

Overview (4/4)

Designed for science majors . . .

Overview (4/4)

Designed for science majors . . .

Web site:http://www.astro.umass.edu/˜weinberg/a114

Requirements (1/3)

Attendance is the single most important way to ensuresuccess in this course.

A114: Lecture 1—29 Jan 2007 Read: Ch. 1-2 Astronomy 114—6/16

Requirements (1/3)

Reading: Assignments in the text for each class willbe given at the end of the preceding class and arerequired. The relevant chapters are also listed in theSyllabus by subject.

Requirements (1/3)

Reading: Assignments in the text for each class willbe given at the end of the preceding class and arerequired. The relevant chapters are also listed in theSyllabus by subject.

Exams: Two in-class one-hour exams (each 20% ofthe final grade) and one final exam with two parts:last unit and cumulative. Each part worth 20%.

Requirements (2/3)

Makeup exam policy: Makeup exams will be given onlyfor documented medical or family emergencies or byprior arrangement.

Requirements (2/3)

Homework: There will be (roughly) weekly homeworkassignments worth 20% of the final grade.

Requirements (2/3)

Homework: There will be (roughly) weekly homeworkassignments worth 20% of the final grade.

Extra credit: There is none.

Requirements (3/3)

Grades will be assigned on a modified straight scale.Scores will be adjusted upward if the exam is toohard.

87% AB

77% BC

67% CD

2 topic exams 40%

1 topic exam at final 20%

1 cumulative exam at final 20%

Homeworks 20%

Requirements (3/3)

Grades will be assigned on a modified straight scale.Scores will be adjusted upward if the exam is toohard.

87% AB

77% BC

67% CD

2 topic exams 40%

1 topic exam at final 20%

1 cumulative exam at final 20%

Homeworks 20%

Academic Honesty is expected of all scientists, andalso of all students of science.

Scientific Notation (1/5)

The numbers encountered in this class are astronomical:

The nearest star is 41,000,000,000,000 kilometersaway

The mass of the sun is2,000,000,000,000,000,000,000,000,000,000,000grams

Scientists have devised a more compact notation fordealing with such numbers called scientific notation.

41,000,000,000,000 kilometers

2,000,000,000,000,000,000,000,000,000,000,000grams

There are really only two important parts to each of thenumbers:

1. The leading digits – which establish the precision ofthe number itself

2. The number of digits – which sets the size ormagnitude of the number

In Scientific notation:

4.1×1013 and 2.0×1033

The “×" is, as it appears, a multiplication:

102 = 10 × 10 = 100

103 = 10 × 10 × 10 = 1,000

104 = 10 × 10 × 10 × 10 = 10,000

105 = 10 × 10 × 10 × 10 × 10 = 100,000

106 = 10 × 10 × 10 × 10 × 10 × 10 = 1,000,000

so 4.5×104 = 4.5 × 10 × 10 × 10 × 10 = 45,000.

Counting zeros and moving the decimal place is aconvenient way of carrying out the multiplication bypowers of tenExample:

Want: 103× 105

103× 10

5= 10 × 10 × 10 × 10 × 10 × 10 × 10 × 10 = 10

The result of that long string of multiplication is that weadd the exponents of the 10’s: 3+5=8

Addition a bit more tricky:

103+10

5= 10×10×10 + 10×10×10×10×10 = 1.01×10

103+10

5= 10×10×10 + 10×10×10×10×10 = 1.01×10

1, 000 + 100, 000 = 101, 000 = 1.01 × 105

103+10

5= 10×10×10 + 10×10×10×10×10 = 1.01×10

1, 000 + 100, 000 = 101, 000 = 1.01 × 105

0.01 × 105+ 1.0 × 10

5= 1.01 × 10

Rule: add the prefix (mantissa) when power of ten(exponent) for the addends is the same

Metric Prefixes

10−15 femto-10−12 pico-10−9 nano-10−6 micro-10−3 milli-10−2 centi-10−1 deci-10 deka-102 hecto-103 kilo-106 mega-109 giga-1012 tera-1015 peta-

Measuring distance

Distance in meters (m)

Energy Output

Energy Source Total Energy (J)

Big Bang 1068

Radio galaxy 1055

Supernova 1046

Sunlight (1 y) 1034

Volcanic explosion 1019

H-bomb 1017

Thunderstorm 1015

Lightning flash 1010

Baseball pitch 102

Typing (per key) 10−2

Flea hop 10−7

Astronomy 114 - UMass Amherstastro.umass.edu/~weinberg/a114/lectures/lec01.pdf · Astronomy 114...

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