Astro 10-Lecture 1:Introductions

Who am I?

Dr. Eric Korpela

korpela@ssl.berkeley.edu

http://setiathome.ssl.berkeley.edu/~korpela/

(510) 643-6538

Course Goals

• To give you an understanding of what science is, how it works, and what it can and can’t tell us.

• To give you an appreciation of the night sky• To make you excited about and interested in

astronomy• To allow you to critically assess popular portrayals

of astronomy

A promise and a warning

The promise:– You will learn a lot.

The warning:– Each lecture builds on material from earlier lectures, so

it’s easy to fall behind and hard to catch up again.

Expected Work-load

• Expect to put in 2-3 hours outside class for each hour of lecture. (6-9 hours per week)

– Read the assigned material before coming to class.

– Homework will be assigned every 2-3 weeks.• Homework is accepted up to 1 week late for half credit

• Homework will not be accepted after solutions are available.

– There will be 2-3 projects assigned during the semester• The will be handed out a long time before they are due.

• DON’T WAIT UNTIL THE LAST MINUTE TO DO THEM!

Exercises, Quizzes and Exams

• There will be an in class exercise or a quiz each week as a means of taking attendance.– If you arrive late and miss a quiz, be sure to let me know

you attended class.

• There will be 3 exams.– In class, one hour followed by a guest lecture.

– Final is non-cumulative.

– Let me know at least 2 weeks in advance if you have a conflict.

Grading

• Grading is on a curve.

• Breakdown

Homework 20%

Exercises and Quizzes 15%

Projects 20%

Exams 45%

What is Astronomy?

Literally: aster = star

+nomie=naming

(Astrology was already taken)

Astronomy, in modern terms, is observational scientific study of the universe and its contents.

Astrophysics is the combination of astronomy with theoretical understanding of the processes taking place in astronomical objects.

A more basic question: What is science?

Is science a collection of facts?

No!

Science is a process. It’s a means by which we try to understand how the world works.

Example:

Watch a football game. Try to figure out the rules without knowing them or having a rule book.

Science is the process of trying to create a universal rule book.

A gallery of the skies

A gallery of the skies

A gallery of the skies

A gallery of the skies

A gallery of the skies

A gallery of the skies

A review of scientific notation.

Astronomy deals with very large and very small numbers…

Distance from Earth to Sun ~

150 000 000 000 meters

Mass of hydrogen atom ~

0.000 000 000 000 000 000 000 000 001 67 kg

1.5x1011 meters

1.67x10-27 kg

A review of scientific notation.

Significant figures… (Number of digits before the ‘x’)

2 significant figures

3 significant figures

1.5x1011 meters

1.67x10-27 kg

How far does light travel in 65.1 millionths of a second?

d=v x t = 3.0x108 m/s x 6.51x10-5 sMultiply the mantissas (the numbers before the ‘x’)

19.53 x 108 x 10-5 m/s sAdd the exponents (the numbers above the 10)

19.53 x 103 m/s sShift the decimal to the first place by adding or subtracting from the

exponent.

1.953 x 104 m/s sRound to the minimum number of significant digits in the original numbers.

2.0 x 104 m/s sCancel units to get the correct units

2.0 x 104 m = 20,000 meters = 12 miles

How long does it take light to get from the Sun to the Earth?

t = d/v = 1.5x1011 m / 3.0x108 m/sDivide the mantissas (the numbers before the ‘x’)

0.5 x 1011 / 108 m / (m/s)Subtract the exponents (the numbers above the 10)

0.5 x 103 m/(m/s)Shift the decimal to the first place by adding or subtracting from the

exponent.

5 x 102 m/(m/s)Round to the minimum number of significant digits in the original numbers.

5.0 x 102 m/(m/s)Cancel units to get the correct units

5.0 x 102 s = 500 s = 8.3 minutes

How fast are you moving right now?

Rotation of the Earth

radius of the earth = Re = 6400 km = 6.4x103 km

1 day = 86400 seconds = 8.64x104 sec

v = d/t = 2Re/1 day

= 4.0x104 km/day / 8.64x104 s/day

= 4.6x10-1 km/s ~ 1000 mph

How fast are you moving right now?

Orbit of the Earth around the Sun

radius of the earth’s orbit = A.U. = 1.5x108 km

1 year = 3.16x107 sec

v = d/t = 2A.U./year

= 9.4x108 km/day / 3.16x107 s/day

= 30 km/s ~ 67 000 mph

How fast are you moving right now?

Orbit of the Sun around the Galaxy

200 km/s ~ 450 000 mph

Movement of Galaxy with respect to the rest of the universe

540 km/s ~ 1.2x106 mph

A reminder: The metric system

Basic units: meter (m), gram (g), second(s)

Prefixes

Giga (G) 109

Mega (M) 106

kilo (k) 103

hecto (h) 102

centi (c) 10-2

mili (m) 10-3

micro () 10-6

nano (n) 10-9

Other units used in Astronomy

Astronomical Unit (AU) = distance from Earth to the Sun

= 1.5x1011 m

Light Year (ly) = distance light travels in one year =

d = v t = 3.0x108 m/s x 3.16x107 s =

9.5x1015 m

Parsec (pc) = 206264.81 AU = 3.26 ly

= 3.1x1016 m

The scale of the universe

How can we understand these distances on a human scale?

The sun is 1.5x1011 m away.

A passenger jet travels at 600 mph ~ 270 m/s

If you could fly to the sun, the trip would take…

t = d/v = 1.5x1011 m / 270 m/s =5.6x108 s = 18 years!

The next nearest star is 4.3 light-years away, 270 000 times as far.

It would take 4.8 million years to get there by jet!

The scale of the universe

• Powers of Ten [video]

SCALE MODELS

Scale of the Solar System

Solar System

Relative Size of Earth and Moon

Relative Sizes of Planets

Distances Between Planets

SCALE MODELS

A scale model of the history of the universe

A scale model of history

The universe is about 13 billion years old.

To make it a bit more comprehensible scale it to 1 day.

A scale model of history

12:00 am 0 seconds The Big Bang!

12:00:03 400 ky The universe becomes transparent

12:22 200 My The first stars form

1:50 1 Gy Milkyway Galaxy forms

3:41 pm 8.5 Gy Solar System forms

4:03 8.7 Gy Earliest indications of life on Earth

7:23 9.5 Gy Continents begin to form

8:52 2.5 Gya Earliest multicellular life forms

10:46 670 Mya First land plants

11:00 530 Mya First insects

11:13 430 Mya First fish

11:35 230 Mya Dinosaurs evolve

11:53 65 Mya Dinosaurs die out

A scale model of history

11:59:26 5 Mya First apes that walk erect (homonoids)

11:59:59.33 100 kya Modern humans appear

11:59:59.93 10 kya Agriculture developed

11:59:59.975 kya Great pyramids built

11:59:59.9987 204 ya American Revolution

11:59:59.99989 18 ya About when most of you were born.

How does science work?

A scientist makes an educated guess about a rule: a hypothesis.– A hypothesis needs to be quantitative.– It needs to make predictions about the behavior of the universe.– A hypothesis builds on existing knowledge of the universe

The hypothesis is tested by experiment or observation.– If the hypothesis fails a test it must be discarded or modified.

Example Hypothesis: All objects fall when dropped….– Is this hypothesis true or false?

A hypothesis that never fails despite repeated tests of its predictions is called a theory. (In science, ‘a theory’ is something that is a near certainty.)

How does science work?

Science isn’t about ‘truth.’ It’s about what has worked so far.

– No hypothesis can be proven to be true. It can only be shown to be false. (A hypothesis must be falsifiable.)

– A complete hypothesis must work at all places and times.

– Only one bad prediction is required to falsify a hypothesis.

• Example: Newton’s Law of Universal Gravitation– superceded by Einstein’s Theory of General Relativity

– still a useful approximation for most situations despite having been falsified.

Things that are not science...

Astrology - It makes predictions, but the theory/method isn’t changed when predictions fail

Creation Science - It makes no testable predictions. Not falsifiable.

Psychic precognition - theory/method isn’t changed when predictions fail.

Religion - Not falsifiable.

’Not science’ does not mean ‘not true’ any more than ‘science’ means ‘truth.’

How would a scientist find the answer the following questions?

How long does it take to cook a turkey?

Why does it take that long to cook a turkey?

The difference between these questions is the difference between observational fact and science.