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To Do Today

Finish up the worksheet from last time: 15 minutes

Class prep & discussion

Overview: Galaxies and Distances

Writing Exercise: Strength on the Sentence Level

5 Minutes: Prep for Class Discussion

How do you feel about the idea in the reading that the Big Bang model can do nothing to say what caused or came before the Big Bang?

The diagram at right shows the different forms of energy in the Universe. What do you think about this information? Are you surprised?

What was one topic in this reading that you would like to know more about (including specific questions)?

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Class Discussion

How do you feel about the idea in the reading that the Big Bang model can do nothing to say what caused or came before the Big Bang?

Class Discussion

The diagram shows the different forms of energy in the Universe. What do you think about this information? Are you surprised?

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Class Discussion

What was one topic in this reading that you would like to know more about (including specific questions)?

What is a Galaxy?

The Wikipedia Definition: “A galaxy is a massive, gravitationally bound system consisting of stars, an interstellar medium of gas and dust, and dark matter.”

M31, from Hubble

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Spiral Galaxies

Andromeda Galaxy or M31.Our nearest large neighbor

“Grand Design” Spirals

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“Grand Design” Spirals

The Whirlpool Galaxy (M51) and an interacting neighbor

Barred Spiral GalaxiesBarred Spiral Galaxy NGC 1300.The Milky Way is also barred

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Elliptical Galaxies

M87 in the Virgo Cluster.Ellipticals look like smooth, featureless “blobs” and show no ordered rotation.

How Galaxies Form

It turns out dark matter is so much more prevalent than “regular” matter, that the gravity of dark matter has a bigger influence on the development of the Universe than the “normal stuff” does.

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How far away are galaxies?

Astronomers measure distances in light years.

Does anyone know what a light year is?

How far away are galaxies?

Astronomers measure distances in light years.

A light year is the distance that a beam of light can travel in a year.

Since light moves at 670 MILLION miles per hour, this is a very long distance

That’s 186,000 miles per second, so in everyday life you never notice that light has a speed.

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…It takes light ___seconds to go from the Earth to the Moon: 238,000 miles

1.3

…It takes light ___ minutes to travel from the Sun to the Earth, 93 million miles away

8.3

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It takes light _____ years to travel from our Sun to the nearest star Proxima Centauri, 2.5 x 1013 miles away

If the Sun were scaled down to the size of a period on a printed page, then Alpha Centauri would be around 8 miles away.

4.25

It takes light _______ years to travel from the center of our own galaxy to the Earth, 1.5 x 1017

miles

25,500

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It takes light ____________ years to travel from Earth to the Andromeda Galaxy, located on the other side of our Local Group of galaxies, 1.7 x

1019 miles away

2.89 million

It takes light _________ years to reach the Virgo cluster of Galaxies, which is

the most massive portion of the Supercluster our Local Group belongs

to, 3.5 x 1020 miles away

60 million

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So galaxies are MILLIONS or BILLIONS of light years away!

These numbers are big and clumsy to work with, so usually we use a different

system . . .

What is a parsec?

A parsec is about 3 light years.

1 kiloparsec is ______ parsecs

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What is a parsec?

A parsec is about 3 light years.

1 kiloparsec is 1000 parsecs

A megaparsec is 1 million parsecs (mega stands for million)

A gigaparsec is 1 billion parsecs (gigastands for billion)

Why parsecs?

Parsecs are a handy length scale:A galaxy can be measured in kiloparsecs(kpc)

The Milky Way is about 20 kpc across, and we’re about 10 kpc from the center

Distances between galaxies can be measured in megaparsecs (Mpc)

The scale of the whole Universe is measured in gigaparsecs (Gpc)

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Distribution of Galaxies

Structures in the Universe: The best place to find a galaxy is next to another one!

Groups

Clusters

Superclusters

Filaments and Voids

Distribution of GalaxiesStructures in the Universe: The best place to find a galaxy is next to another one!

GroupsClusters

Superclusters

Filaments and Voids

The local group includes two

dominant spiral galaxies, the Milky Way & Andromeda,

and about 30 dwarf galaxies

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Distribution of GalaxiesStructures in the Universe: The best place to find a galaxy is next to another one!

Groups

ClustersSuperclusters

Filaments and Voids

The Virgo Cluster is the closest

nearby cluster, at about 17 Mpc. It contains about 1500 member

galaxies!

Distribution of GalaxiesStructures in the Universe: The best place to find a galaxy is next to another one!

Groups

Clusters

SuperclustersFilaments and Voids

Superclusters are “clusters of

clusters” and can extend for

hundreds of millions of light

years.

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Distribution of GalaxiesStructures in the Universe: The best place to find a galaxy is next to another one!

Groups

Clusters

Superclusters

Filaments and VoidsThis simulation

contains more than 10 billion particles, and

attempts to trace galaxy, cluster &

superclusterformation.

Essay 1 . . .

We’ve still got one more thing to do today!

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Essay 1 . . .

Find your “starred” sentence and write it down (including any errors you notice!)With your partner, discuss what would make the sentence stronger.

Variation? Clauses? Rearrangement?Word choice? Precision? Easy to understand?

Work together to rewrite both of your sentences.Check out the “Writing Style” section of Easy Writer for tips

Reading Assignment

Hooper, Chapter 2

Ferreira, Chapter 3

Check out the reading questions online!

Please BRING these 2 books with you to class next week

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Essay 1 Exercise: Be concise!

Find your longest sentence and write it on a piece of paperWe’ll pass the papers around the room and shorten each sentence that comes our way by ONE WORD.Tip for conciseness from Easy Writer:

Eliminate redundant wordsEliminate “empty” wordsReplace wordy phrasesSimplify sentence structureTry using the active voice