ASTRO 101
Principles of Astronomy
Instructor: Jerome A. Orosz
(rhymes with
“boris”)
Contact:
• Telephone: 594-7118
• E-mail: orosz@sciences.sdsu.edu
• WWW:
http://mintaka.sdsu.edu/faculty/orosz/web/
• Office: Physics 241, hours T TH 3:30-5:00
Text:
“Discovering the Essential Universe,
Fifth Edition”
by
Neil F. Comins
Course WWW Page
http://mintaka.sdsu.edu/faculty/orosz/web/ast101_fall2012.html
Note the underline: … ast101_fall2012.html …
Also check out Nick Strobel’s Astronomy Notes:
http://www.astronomynotes.com/
Syllabus:
http://mintaka.sdsu.edu/faculty/orosz/web/ast101_fall2012/syllabus1/index.html
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Safety
Prerequisites
Homework
Grades
Conduct in class
Why Take this Class?
We want to understand and
appreciate everything in
the Universe!
Since the earliest recorded times,
people have looked up at the sky
and wondered about the things
they saw.
Most early cultures had extensive
mythologies relating to the
workings of the Earth and things
in the sky.
We live in interesting times. We are
in a position to investigate and
answer many basic and profound
questions about our world and
beyond...
• Here are a few representative object categories we can observe
We live in interesting times. We are
in a position to investigate and
answer many basic and profound
questions about our world and
beyond.
In this course we will survey such
topics as…
The Earth
• Why are there seasons on Earth?
• What causes the day/night cycle?
• How old is the Earth?
The Sun
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What is it?
How does it shine?
How old is it?
Will it go on forever, or will it “die”?
The Moon
• What is it?
• Where did it come from?
• Is there life on it?
The Solar System Planets
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What are they?
What are they like?
Where did they come from?
Do they have life?
The Stars
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What are they?
Why are some stars red and other ones blue?
Why do they twinkle?
How old are they?
Will they last forever, or will they “die”?
Galaxies
• What are galaxies?
• How big are they?
• What is the Milky Way? Is it a typical
galaxy?
Strange Objects
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What is a White Dwarf?
What is a Neutron Star?
What is a Black Hole?
What is a Quasar, and how do they work?
What is a Nova explosion? What is a
Supernova explosion?
Deep Questions
• How big is the Universe?
Deep Questions
• How big is the Universe?
• Does the Universe have a beginning and an
end? If so, how old is it?
Deep Questions
• How big is the Universe?
• Does the Universe have a beginning and an
end? If so, how old is it?
• The meaning of infinity…
The Meaning of Infinity
• Suppose the universe is infinite in size and in
age:
The Meaning of Infinity
• Suppose the universe is infinite in size and in
age:
– Then everything that is possible to happen has
already happened, an infinite number of times.
The Meaning of Infinity
• Suppose the universe is infinite in size and in
age:
– Then everything that is possible to happen has
already happened, an infinite number of times.
– Therefore there are exact copies of you, me this
classroom, this earth, etc. somewhere out there.
The Meaning of Infinity
• Suppose the universe is infinite in size and in
age:
– Then everything that is possible to happen has
already happened, an infinite number of times.
– Therefore there are exact copies of you, me this
classroom, this earth, etc. somewhere out there.
– There are also an infinite number of near copies of
you out there, e.g. someone like you but with
different hair, more money, etc.
Deep Questions
• How big is the Universe?
• Does the Universe have a beginning and an
end? If so, how old is it?
• The meaning of infinity…
Deep Questions
• How big is the Universe?
• Does the Universe have a beginning and an
end? If so, how old is it?
• The meaning of infinity…
• Is there other life out there?
Deep Questions
• How big is the Universe?
• Does the Universe have a beginning and an
end? If so, how old is it?
• The meaning of infinity…
• Is there other life out there?
• While your friends are thinking about what
socks to wear, we will ponder these and
other questions!
Course Philosophy
• We will emphasize understanding concepts, not
just memorizing jargon.
• We will spend a great deal of time discussing
how we know what we know, e.g. the use of the
Scientific Method.
• A good understanding of the Scientific
Method will benefit you in situations beyond
this class, so the effort is worthwhile.
Next:
• Math Review
• Introduction to the Sky
Math Review
• Powers of 10 and a sense of scale:
– 1-1_SizesUniverse.html
– http://micro.magnet.fsu.edu/primer/java/scienceopticsu/powersof10/
– http://www.wordwizz.com/pwrsof10.htm
Math Review
• Powers of 10 and a sense of scale:
Math Review
• What is a googol?
A googol is
10,000,000,000,000,000,000,000,000,
000,000,000,000,000,000,000,000,000,
000,000,000,000,000,000,000,000,000,
000,000,000,000,000,000,000
(i.e. a 1 followed by 100 zeros)
Scientific Notation
• In Astronomy, and elsewhere, large
numbers are often needed.
• A more compact notation is needed, usually
called Scientific Notation. It is based on
powers of 10.
Powers of 10
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102 = 10 x 10 = 100
103 = 10 x 10 x 10 = 1000
104 = 10 x 10 x 10 x 10 = 10,000
etc…
Powers of 10
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102 = 10 x 10 = 100
103 = 10 x 10 x 10 = 1000
104 = 10 x 10 x 10 x 10 = 10,000
etc…
100 = 102
1000 = 103
10,000 = 104
10,000,000,000,000,000,000,000,
000,000,000,000,000,000,000,
000,000,000,000,000,000,000,
000,000,000,000,000,000,000,
100
000,000,000,000,000 = 10
a googol =
100
10
To write out a number given as a
power of 10, the number of zeros
is the given by the exponent.
Example: 104 = 10,000
To write out a long number
(consisting of a 1 followed by
zeros) as a power of 10, the
exponent is the number of zeros.
Example 100,000 = 105
Some Rules for Powers of 10
• To multiply two different powers of 10, add the
exponents:
 102 x 103 = 102+3 = 105
 103 x 103 = 106
• To divide two different powers of 10, subtract
the exponents:
 104 102 = 104-2 = 102
 105 103 = 105-3 = 102
105 = 100,000
104 = 10,000
103 = 1000
2
10 = 100
101 = 10
100 = ?
105 = 100,000
104 = 10,000
103 = 1000
2
10 = 100
101 = 10
100 = 1
105 = 100,000
104 = 10,000
103 = 1000
2
10 = 100
101 = 10
100 = 1
10-1 = ?
105 = 100,000
104 = 10,000
103 = 1000
2
10 = 100
101 = 10
100 = 1
10-1 = 1/10 = 0.1
105 = 100,000
104 = 10,000
103 = 1000
2
10 = 100
101 = 10
100 = 1
10-1 = 1/10 = 0.1
10-2 = ?
105 = 100,000
104 = 10,000
103 = 1000
2
10 = 100
101 = 10
100 = 1
10-1 = 1/10 = 0.1
10-2 = 1/100 = 0.01
What about other numbers, like
6,000,000?
6,000,000 = 6 x 1,000,000
6,000,000 = 6 x 1,000,000
= 6 x 106
6,000,000 = 6 x 1,000,000
= 6 x 106
1,200,000 = 1.2 x 1,000,000
= 1.2 x 106
How do we say it?
How do we say it?
• 103 = 1,000 = one thousand
How do we say it?
• 103 = 1,000 = one thousand
• 106 = 1,000,000 = one million
How do we say it?
• 103 = 1,000 = one thousand
• 106 = 1,000,000 = one million
• 109 = 1,000,000,000 = one billion
How do we say it?
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103 = 1,000 = one thousand
106 = 1,000,000 = one million
109 = 1,000,000,000 = one billion
1012 = 1,000,000,000,000 = one trillion
How do we say it?
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103 = 1,000 = one thousand
106 = 1,000,000 = one million
109 = 1,000,000,000 = one billion
1012 = 1,000,000,000,000 = one trillion
1015 = 1,000,000,000,000,000 = one quadrillion
How do we say it?
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103 = 1,000 = one thousand
106 = 1,000,000 = one million
109 = 1,000,000,000 = one billion
1012 = 1,000,000,000,000 = one trillion
1015 = 1,000,000,000,000,000 = one quadrillion
Many numbers in Astronomy have no common
names, and are written in scientific notation.
How do we imagine it?
How do we imagine it?
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Example: what is my age, in seconds?
How do we imagine it?
• Example: what is my age, in seconds?
(a) about 1 million seconds
How do we imagine it?
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Example: what is my age, in seconds?
(a) about 1 million seconds
(b) about 1 billion seconds
How do we imagine it?
•
Example: what is my age, in seconds?
(a) about 1 million seconds
(b) about 1 billion seconds
(c) about 1 trillion seconds
How do we imagine it?
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Example: what is my age, in seconds?
(a)
(b)
(c)
(d)
about 1 million seconds
about 1 billion seconds
about 1 trillion seconds
about 1 quadrillion seconds
How do we imagine it?
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Example: what is my age, in seconds?
(a)
(b)
(c)
(d)
about 1 million seconds
about 1 billion seconds
about 1 trillion seconds
about 1 quadrillion seconds
Hint: I am 45 years old.
Well, there are
60 seconds in one minute,
60 minutes in one hour,
24 hours in one day,
and 365.25 days in one year.
Well, there are
60 seconds in one minute,
60 minutes in one hour,
24 hours in one day,
and 365.25 days in one year.
So,
age = 45 x 60 x 60 x 24 x 365.25
= 1.420 x 109 seconds
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Example: what is my age, in seconds?
(a)
(b)
(c)
(d)
about 1 million seconds
about 1 billion seconds
about 1 trillion seconds
about 1 quadrillion seconds
Hint: I am 45 years old.
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Example: what is my age, in seconds?
(a)
(b)
(c)
(d)
about 1 million seconds
about 1 billion seconds
about 1 trillion seconds
about 1 quadrillion seconds
Hint: I am 45 years old.
1 billion sec = 31 yr + 251 d + 7 hr + 46 min
Which makes more sense?
Which makes more sense?
“I am 1.42 billion seconds old.”
Which makes more sense?
“I am 1.42 billion seconds old.”
“I am 45 years old.”
Which makes more sense?
“I am 1.42 billion seconds old.”
“I am 45 years old.”
“My neighbor Francis was
3.13x109 seconds old.”
Which makes more sense?
“I am 1.42 billion seconds old.”
“I am 45 years old.”
“My neighbor Francis was
3.13x109 seconds old.”
“Francis was 99 years old.”
Where possible, scale things to
sensible units:
Where possible, scale things to
sensible units:
Example: “This black hole has a
mass 7 times larger than the
Sun’s mass.”
Where possible, scale things to
sensible units:
Example: “This black hole has a
mass 7 times larger than the
Sun’s mass.”
“This black hole has a mass of
34
1.39x10 grams.”
Next:
Discovering the Night Sky