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Galaxies

Seeing the Universe

Section 3

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What Exactly are They?

Galaxies are groups of stars, gas, anddust held together by gravity.

May contain as many as one trillion stars

They vary in size but our galaxy (theMilky Way) is 100,000 light yearsacross

The closest galaxy to the Milky Wayis Andromeda

2 million li ht ears awa

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Types of Galaxies

Spiral have spiral arms that windoutward from inner regionsThe Milky Way and Andromeda are spiral

(so is the picture in the background) Some are barred spirals where the

arms extend from a central bar ofstars

Elliptical shaped like large 3-Dellipses (like a football). Some are large enough that several

Milky Ways could fit inside of them

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Irregular just like it sounds, theydont have a definite shape and dontfit easily into other classifications

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EllipticalGalaxy

Notice otherspiral galaxiesin the

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An irregular

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The Milky Way

Our home galaxy is 100,000 lightyears across

Our solar system is about 30,000 Ly

from the center and makes one full orbitin 240 mil yearsThis means that were travelling at 235 km/s

If theres low light pollution, you cansee the Milky Way on a clear night

It looks like a band of misty lightstretching through the night sky

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The Milky Way as seenfrom a road in Death

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Expansion of the Universe

What does an ambulance sound likeas it passes you?

Have you noticed the drop in pitch as it

travels away from you?This is called the Doppler effect

Light from other stars does the same

thing!

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The Doppler Shift

Just like sound waves, light that travelstoward us is compressed and light thattravels away is elongated

Think about the ambulance, the pitchlowers because the sound waves are beingstretched out

Light that is moving away from us

(stretched) is shifted toward the redend of the color spectrum

Light that is moving toward us(compressed) is shifted toward the blue

end

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Elongated

Compressedwaves

Shifted

Shifted blue

Normal

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Red Shift

Edwin Hubble discovered that allgalaxies outside of our Local Grouphave a red shift

What direction are all of these galaxiesmoving then?

If they all have red shifted light, they

all must be moving away from theEarth

Scientists determined that if theyre

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The Big Bang Theory

States that the universe began 12-15billion years ago in a massiveexplosion

The entire universe began to expandeverywhere at the same time

As matter cooled, it clumpedtogether to form hydrogen andhelium gasses Eventually, gravity caused this matter to

compact and form the first stars

The first stars were born after about one

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Faith and the Big Bang

Faith is being sure of what we hopefor, and certain of what we cannotsee Heb. 11:1

Take comfort in the complexity of lifeand the universe itself

The Bible says that the wisdom of men

is like foolishness to God. 1 Cor. 1:25,3:19

The goal of science is to explainEVERYTHING and scientists are going to

do just that.