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January 10, 2006
Astronomy 2010
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What is Astronomy?
The study of objects outside the Earth. Examples:
The Moon
• What phase is the Moon in tonight? Waxing or waning?
Planets, comets, asteroids
• Are any planets visible? Comets?
The Sun and stars
• How do stars form and why do they shine?
• Do other stars have planets orbiting them?
• Could there be life on those planets?
Lots of other stuff: galaxies, supernovae, black holes, …
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Numbers
Scientific Notation (power of ten)
1,000,000 = 10x10x10x10x10x10 = 106
$150,000,000,000,000 = 150x1012 = $1.5x1014
1 nanosecond = 0.000,000,001 seconds = 10-9 seconds
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The Milky Way
Sun is ~ 30000 LY from the center of our Galaxy.
From our location within the galaxy, we cannot see through its far rim
because the space between stars is not empty – interstellar dust or gas
which absorbs visible light.
The interstellar gas is the fuel for the formation of stars.
Yet, interstellar material is very sparse, space between stars is quite
empty – much more so than an vacuum one can achieve in the
laboratory on Earth.
Possibility of dark matter.
Star Clusters – contain up to hundreds of thousands of stars – light
years across.
Star have a long life (billions of years) but not infinite – they die or
collapse in spectacular ways.
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Nearby objects (Orion Nebula in the Magellanic Cloud)
• Our galaxy is not unique .
• Many other discovered & studied.
• Some are close to us
• Magellanic clouds
• Most are at enormous distances.
• Nearest large galaxy is Andromeda,
or M31.
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Local group of galaxies
• M31 is part of a small cluster of over 40
galaxies one calls the local group.
• At distances of about 10 to 15 million LY,
one finds other small galaxy groups or
clusters.
• At about 50 million LY, one finds a very
large cluster containing thousands of
galaxies – called the Virgo cluster.
• Some of the observed clusters appear to
form super clusters.
• Our local group and the Virgo cluster are
part of one such supercluster which
stretches over a diameter of 60 million
LY.
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Farthest galaxy (red object)
about 1.3 x 1010 LY
Galaxies are collections of
about 1011 stars
Andromeda galaxy
distance 2 x 106 LY
nearest star
4.3 LY = 9.6 x 1012 km
= 64,000 AU
Sun
1 AU = 1.5 x 108 km
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We’ll cover other topics as background:
History of astronomy
Newton’s laws of motion and gravity
Orbits and motion of objects
Geology of the Earth
Comparative geology of other planets
Atoms and light
Spectra measured by telescopes
Nuclear fusion
The Sun and stars
Special and general relativity
Fusion, black holes, and cosmology
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What is Science?
A science is a methodological study following the scientific
method.
The scientific method has 5 steps:
Observation
• Observe some phenomenon to be studied
Hypothesis
• Develop a hypothesis of the phenomenon
Prediction
• Derive a testable prediction from the hypothesis
Measurement
• Make a measurement that tests the prediction
Conclusion
• Verify or refute the prediction, adjust the hypothesis as necessary
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Laws of Nature
Some scientific hypotheses are so well verified in a
wide variety of situations that they become elevated
to the status of “laws of nature”.
Newton’s laws of motion and gravitation
Conservation of momentum and energy
Ideal gas law
Conservation of mass/atoms
Cell theory
DNA
Evolution
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Numbers
Word
Number
trillion
1,000,000,000,000 1012
billion
1,000,000,000
109
Giga (G)
million
1,000,000
106
Mega (M)
thousand
1,000
103
kilo (k)
1
100
thousandth
0.001
10-3
milli (m)
millionth
0.000001
10-6
micro (µ)
billionth
0.000000001
10-9
nano (n)
trillionth
0.000000000001
10-12
pico (p)
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Tera (T)
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Speed of Light
How fast does light travel?
About 300,000 km/s = 11,000,000 km/hr
The distance that light travels in one year is called a
light-year, abbreviated ly = 9.51012 km/year.
While this is a large distance, it is useful for quoting
distances to other stars.
Can be generalized to include light-second, light-day, etc.
The Moon is about 1.3 light-seconds from Earth.
The Earth is about 8 light-minutes from the Sun.
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Astronomy is a Time Machine
When we observe a star that is 100 light-years
distant, then the light took 100 years to reach us.
We are seeing it as it was 100 years ago.
The nearest galaxy is about a million light-years
from Earth. We see it as it was 1 million years ago.
The most distant objects observed are about 10
billion ly from Earth. The light we see left the
object 10 billion years ago!
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Discussion Question
What are some of the things you wish to learn about
in this course?
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