Transcript Unit 1

Astronomy 103
Lecturer: Prof. Alex Lazarian
Office Location: 6289 Chamberlin Hall
Email:
[email protected]
Website: http://www.astro.wisc.edu/~lazarian/Spring2012
Office Hours: Mon. 11am-1pm, Wed. 11am-1pm. Meetings at a different time can also be arranged.
Course Reading: Pathways to Astronomy Schneider & Arny 3nd edition
Exams:
th
0 training exam -- 0% (Feb. 15)
1st exam – 25% (Feb. 29)
2nd a exam —25% (March 28) you choose either a or b grade
2nd b exam —25% (April 16) you choose either a or b grade
final exam for group 8:50 class—30% (May 15)
For group 9:55 class-- 30% (May 16)
total for homework, quizzes, participation in the work in class -- 20%
Students who work for honors should see me after the class
Main Ideas to be covered:
*Subject of astronomy (Units 1--4)
*Observations of planets and stars (Units 5--12)
*Laws of gravity, dark matter (Units 14-20)
*Light, atoms, spectra (Units 21--30)
*Stars: Sun as an example (Units 51--53)
*Learning about stars (Units 54--60)
*Birth and evolution of stars (Units 61ó64)
*When the fuel begins to run out (Units 65--67)
*Supernova, neutron stars and black holes (Units 68--69)
*Star clusters (Unit 70)
*Our galaxy- Milky Way (Units 71--74)
*Galaxies and quasars (Units 75--78)
*The expanding Universe (Units 79--84)
*Life in the Universe (Units 85--86)
Why do I study Astronomy?
“Education is kindling of a flame, not the filling of a vessel”
Socrates
My goals for the course:
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Share my excitement with Astrophysics
Provide a survey of most of Astronomy
Show that Astronomy is a quest for our origins
Show how science is done
Look at my personal web page to know more about my research
http://www.astro.wisc.edu/~lazarian/
Your book is good but contains mistakes
See, for instance p. 38, problem 3
We shall be correcting mistakes during the lectures
We shall use clickers: Enroll at www.eInstruction.com
The Earth
• The Earth is a planet, a body in
orbit around a star (The Sun)
• Radius: 6371 km (3909
miles)
• Mass: around 6 billion
trillion tons
• Actual value:
5,970,000,000,000,000,000,000,000 kg
• Too many zeros!
Use 5.97  1027 kg, instead!
Metric System
•Easier to use (everything is a factor of 10!)
The Moon
• The Moon is a satellite, a
body orbiting a planet
– Rocky world, littered with
craters
• Bombarded by meteors
• Where are the Earth’s craters?
– Smaller than the Earth
• Less than 1/80 the mass
• ¼ the diameter of Earth
– Small, so cooled quickly!
– Cold, airless and lifeless
The Planets
Why are they so
different?
How did they
get this way?
• Wide variety of planets in the Solar System
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Rocky, hot and airless worlds
Gas giants and ringed wonders
Cold planets of blue methane
Tiny icy bodies
The Sun
• The Sun is a star, a
huge ball of gas held
together by gravity and
generating light
through thermonuclear
reactions
• Source of all energy in
the Solar System
• 100x wider than the
Earth, and 300,000x as
massive!
• Young, yet old
– 4 billion years old
– Will last another 5 or
6 billion years
The Solar System
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•
•
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Planets, asteroids, comets and dust all held together by the Sun’s gravity
Everything goes around the Sun on elliptical paths called orbits
All orbits lie in the same plane, like peas rolling around on a dinner plate
Too big to describe using meters – we need something more convenient
A convenient measure –
the Astronomical Unit
• It is convenient to measure planetary
distances using the Astronomical
Unit, or AU
• 1 AU = average distance between
the Earth and the Sun
• 1 AU ~ 150 million km
Some planetary distances:
• Mercury: 0.4 AU
• Mars: 1.5 AU
• Saturn: 10 AU
• Pluto: 40 AU
The Milky Way Galaxy
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The Milky Way galaxy contains billions of
stars, being born, aging and dying with a
whisper or a bang.
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Where do stars come from?
How do they age?
How and why do they die?
This process is called Stellar Evolution!
A New Measure of Distance
• Stars in the Milky Way are
very far apart
– Nearest star is 40 trillion km
away – too large to imagine!
– How about hundreds of
thousands of AU? No, still too
big.
– Light travels 10 trillion km in
one year, so we’ll use the light
year (ly) as an easy-to-imagine
measure of distance
– It takes light 4.1 years to travel
from Proxima Centauri to
Earth, so the distance to this
star is 4.1 ly.
Getting to Know the Neighborhood
• The Universe is “clumpy” –
galaxies tend to pull together by
gravity
Central region of the Virgo Cluster
– Our immediate neighborhood is
called the Local Group, a cluster of
around 3 dozen galaxies (3 million
light years across
– The Local Group is part of the Virgo
Cluster, a large (collection of
smaller clusters and groups of
galaxies
– Superclusters: collection of larger
clusters
– The Universe – simply everything!
A Sense of Scale I
A Sense of Scale II
Outward to the
Universe!
The Metric System
English Units (Distance)
12 “lines” = 1 inch
12 inches = 1 foot
3 feet
= 1 yard
5.5 yards = 1 rod
4 rods
= 1 chain
10 chains = 1 furlong
8 furlongs = 1 mile
3 miles
= 1 league
Metric Units
10 millimeters
= 1 centimeter
100 cm
= 1 meter
1000 m
= 1 kilometer
1000 milligrams = 1 gram
1000 g
= 1 kilogram
• Metric Units are
internationally accepted
Units. Used in Astronomy.
Scientific Notation
• 0.0000001 meters is difficult to
write – too many zeros!
• Can use scientific notation to
simplify it.
• 0.0000001 m = 110-7
• Move the decimal place seven
places to the left to determine the
“power” of ten
– Moving it to the left makes the
“power” negative
– Moving it to the right makes the
“power” positive
Commonly used prefixes
Number
Scientific
Notation
Prefix
Abbreviation
1,000,000,000
1  109
giga
G
1,000,000
1  106
mega
M
1,000
1  103
kilo
k
1  10-
centi
c
1  10-
milli
m
1  10-
micro

1  10-
nano
n
0.01
0.001
0.000001
0.000000001
2
3
6
9
Special Units
• The Light Year (ly)
– Distance light travels in
1 year
– Equivalent to a “lookback time”, as the light
we see from a star left a
long time ago
– Example: Proxima
Centauri is 4.1 ly away,
so the light we see from
it today left the star 4.1
years ago!
• The Parsec (pc)
– “PARallax SECond”
– Distance to a body whose
parallax motion covers 1
second of arc (See Unit 5!)
– 1 pc = 3.26 ly
A Sense of Scale