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Objective: To define a light year in order to describe the size of galaxiesAstronomy Note: How big are galaxies?

Drill: 1. Take out yesterday’s lab sheet. 2. Get a new ditto from the SET. 3. Complete Activity 1, #1.

Galaxies and Light Years

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Activity 1: Galaxy Recap

Open Your Textbook to page 145. Read about our galaxy. Brain Pop: Galaxies

Galaxies and Light Years

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Activity 2: What is a Light Year?In order to understand the differences among the various galaxies within the universe, you need to understand the idea of “light years.” A light year is a unit of distance equal to the distance that light can travel in one year. Since the speed of light is 300,000 kilometers per second, light travels about 9.5 trillion kilometers in one year. So, what does this mean?

Galaxies and Light Years

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Activity 2: What is a Light Year?Let’s think about it in a different way. For example, if you were riding in a car traveling at the speed of light, in one minute you could travel over 11 million miles, in an hour over 660 million miles. At this speed, it would take you about 100,000 years to go from one end of the galaxy to the other (not counting gas and munchie stops!).

Galaxies and Light Years

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Activity 2: What is a Light Year?But, why would you want such a big unit of distance, anyway? On Earth, a kilometer measures distance just fine. For example, it’s a few hundred kilometers from New York City to Washington, DC, and it’s a few thousand kilometers from California to Maine. However, in the universe the kilometer is too small to be useful.

Galaxies and Light Years

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Activity 2: What is a Light Year?Think of it this way: the distance to the next nearest galaxy, the Andromeda Galaxy, is 21 quintillion kilometers. That’s 21,000,000,000,000,000,000 kilometers! Obviously this number is so large that it is difficult to write and interpret. Therefore, scientists use light years.

Galaxies and Light Years

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Define light year, and explain why light years are used in astronomy.

A light year is a unit of distance equal to the distance that light can travel in one year. We use light years in astronomy because the distances are huge, so we need bigger units to measure with.

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Activity 3: Comparing Galaxies?

Chart 1: Sample Galaxy Characteristics

Galaxies and Light Years

Characteristics Milky Way

Andromeda

Virgo A M32

Type of Galaxy Spiral Spiral Elliptical Elliptical

Diameter (light years)

30,000

165,000 120,000 8,000

Est. # of Stars within Galaxy

100 billion

200 billion 2.7 trillion2,700 billion

3 billion

Distance from Milky Way (light

years)

2,900,000 60,000,000

2,900,000

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List the galaxies in order from smallest to largest.a. M32b. Milky Wayc. Virgo Ad. Andromeda

Pictures taken from space of the galaxies Andromeda, Virgo A, and M32 show that Virgo A is the brightest galaxy of the three. Explain why Virgo A would be the brightest galaxy.

a. By far Virgo A has the most number of stars.

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Activity 4: Quick Check

1. What is the name of our galaxy? 2. What characteristic do scientists use

to classify galaxies? 3. What does a light year measure? 4. What are the 3 categories for

galaxies?

Galaxies and Light Years

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HOMEWORK:

1. In your Log Book, write at least 5 good questions you currently have about astronomy.

2. Complete Class Ditto.3. Expert!!!

Galaxies and Light Years