Transcript Astro 10 Lecture 1 - Intro to Astronomy

Astro 10-Lecture 1:
Introductions
Who am I?
Dr. Eric Korpela
[email protected]
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
Exercises and Quizzes
Projects
Exams
20%
15%
20%
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
1.5x1011 meters
Mass of hydrogen atom ~
0.000 000 000 000 000 000 000 000 001 67 kg
1.67x10-27 kg
A review of scientific notation.
Significant figures… (Number of digits before the ‘x’)
1.5x1011 meters
2 significant figures
1.67x10-27 kg
3 significant figures
How far does light travel in 65.1 millionths of a
second?
d=v x t = 3.0x108 m/s x 6.51x10-5 s
Multiply the mantissas (the numbers before the ‘x’)
19.53 x 108 x 10-5 m/s s
Add the exponents (the numbers above the 10)
19.53 x 103 m/s s
Shift the decimal to the first place by adding or subtracting from the
exponent.
1.953 x 104 m/s s
Round to the minimum number of significant digits in the original numbers.
2.0 x 104 m/s s
Cancel 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/s
Divide 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 = 2Re/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 = 2A.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)
Mega (M)
kilo (k)
hecto (h)
centi (c)
mili (m)
micro ()
nano (n)
109
106
103
102
10-2
10-3
10-6
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
12:00:03
12:22
1:50
3:41 pm
4:03
7:23
8:52
10:46
11:00
11:13
11:35
11:53
0 seconds
400 ky
200 My
1 Gy
8.5 Gy
8.7 Gy
9.5 Gy
2.5 Gya
670 Mya
530 Mya
430 Mya
230 Mya
65 Mya
The Big Bang!
The universe becomes transparent
The first stars form
Milkyway Galaxy forms
Solar System forms
Earliest indications of life on Earth
Continents begin to form
Earliest multicellular life forms
First land plants
First insects
First fish
Dinosaurs evolve
Dinosaurs die out
A scale model of history
11:59:26
11:59:59.33
11:59:59.93
11:59:59.97
11:59:59.9987
11:59:59.99989
5 Mya
100 kya
10 kya
5 kya
204 ya
18 ya
First apes that walk erect (homonoids)
Modern humans appear
Agriculture developed
Great pyramids built
American Revolution
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.