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Astronomy 110Lecture 1

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Why Astronomy• It is part of our story: What we are, where we

came from and where we will go.• It can explain features of the world around us.• We Calibrate our Scale

– A Sense of Perspective– A Sense of Place

The plan: Get the facts, but a lot of attention to the how. Our understanding is built on some simple observations made by many people for many years. Without the how – how can you tell it from Astrology?

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The Universe in Space: Structure is Hierarchical

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Home

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The Utility Room: Heat, Light, Power

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The Neighborhood

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We have many motions – even when we are standing still.

The Earth Spins: ~500m/sec (1000mi/hr)

We Orbit the Sun: ~30km/sec (17 miles/sec)

The Universe in Motion:

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. Our Galaxy would probably look something like this when seen by a distant observer

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Since We are Inside the Milky Way, We See The Disk of the Milky Way as a Bright Stripe Crossing the Night Sky

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Our Sun moves in the local group of stars: 20km/sec

That group orbits the Milky Way Galaxy: ~200km/sec

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The Universe of stars is a lonely, anonymous place.

For their size, stars are very far apart and almost never collide.

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Galaxies are strongly clustered and frequently collide.In the “Grapefruit” universe a rich cluster of galaxies would be about 50 feet across and contain thousands of grapefruits.

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The Universe in Time: The Universe is evolving at all scales.

Change is the rule, not the exception. But how do we see it?

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The lights of stars that were extinguished ages ago still reaches us. So it is with great men who died centuries ago, but still reach us with the radiations of their personalities.-- Kahlil Gibran

Light moves at a speed of

So it takes about 8min to get here from the Sun

1 Year = 365 days X 24 hours/day X 60 min/hour X 60 sec/hour

1 Year = 3.65X2.4X6.X6X105 sec~3X107 sec

(Actually close to 10π million seconds)

83 10 m / sec×

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We are not quite an afterthought – but its close.

Lets use the Milky Way as a clock:

1 Galactic Year is 230 million solar years

So the age of the Universe is:

15 billion solar years/230 million solar years

= ?

The age of the solar system is: ? (~5×109 Solar years)

The Earliest Human- like Critters: ? (~106 Solar years)

Civilization (such as it is): ? (~104 Solar years)