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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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NumbersScientific 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 WaySun 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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• 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.

Local group of galaxies

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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 gravityOrbits and motion of objects

Geology of the EarthComparative geology of other planets

Atoms and lightSpectra measured by telescopes

Nuclear fusionThe Sun and stars

Special and general relativityFusion, 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 NatureSome 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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NumbersWord Number Sci. Not. Prefix

trillion 1,000,000,000,000 1012 Tera (T)

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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Speed of LightHow 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 = 9.51012 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 MachineWhen 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 QuestionWhat are some of the things you wish to learn about in this course?