1- Where is our sun in the H-R diagram?2- What color is our sun?3- How much longer will our sun last?4- What is the next stage of our sun?

Chapter 26 Stars and Galaxies

Section 3 Galaxies

Chapter 26 Section 3Before you read - write the reading’s objectives in this space:1 – _____________________________________________________________________________________________________________________________________________________________________2 – _____________________________________________________________________________________________________________________________________________________________________3 - ______________________________________________________________________________________________________________________________________________________________________

Chapter 26 Section 3Before you read - write the reading’s objectives in this space:1 – Explain the same natural laws that apply in the Milky Way galaxy also apply in other galaxies

2 – Compare the three main types of galaxies.

3 – Describe the Milky Way galaxy and the Sun’s position in it.

What is a galaxy? _______________________________________________________________________What is our galaxy called? _______________________It contains 400 billion stars, by most recent estimates, including the Sun.

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What is a galaxy? A large group of stars, gas, and dust held together by gravity.What is our galaxy called? The Milky Way It contains 400 billion stars, by most recent estimates, including the Sun.

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Describe spiral galaxies. _________________________

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Describe spiral galaxies. Spiral galaxies have spiral arms that wind outward from the galaxy’s center. These spiral arms are made up of bright stars, dust, and gas.

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Describe barred spiral galaxies. ________________________________________________________________________________________________________

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Describe barred spiral galaxies. Barred spirals have spiral arms extending from a large central bar of stars, dust, and gas that passes through the center, or hub, of the galaxy.

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Describe elliptical galaxies. ________________________

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Describe elliptical galaxies. Elliptical galaxies are shaped like large, three-dimensional ellipses. Many are football-shaped, but other are spherical.

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Describe irregular galaxies. ________________________

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Describe irregular galaxies. Most galaxies that aren’t elliptical or spiral are considered irregular galaxies. They take many different shapes and contain 100 million to 10 billion stars, making them larger than dwarf ellipticals but smaller than spirals.

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Andromeda Galaxy – our next nearest “galactic neighbor.” Since the light from this galaxy left 2.5 million years ago, it’s like looking into the past 2.5 million years.

Just as stars are grouped together within galaxies, galaxies are grouped into clusters. What cluster does our Milky Way galaxy belong to? __________________________________________________About how many galaxies are in our group? ________________ ___________________________________________________________________________________________________What is the largest galaxy in our group?_____________________

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Andromeda Galaxy – our next nearest “galactic neighbor.” Since the light from this galaxy left 2.5 million years ago, it’s like looking into the past 2.5 million years.

Just as stars are grouped together within galaxies, galaxies are grouped into clusters. What cluster does our Milky Way galaxy belong to? The Local Group.

About how many galaxies are in our group? It is a relatively small cluster containing about 45 galaxies of various types and sizes but most are dwarf elliptical galaxies.

What is the largest galaxy in our group? Andromeda

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According to current astronomers, how do galaxies form? ____________________________________________________________________________________________________________________________________________________________________________________

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According to current astronomers, how do galaxies form? Galaxies grow by absorbing or merging with other smaller objects. Galaxy collisions have a strong effect on the overall structure and shape of the colliding galaxies.

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What happens to individual stars within colliding galaxies?________________________________________________________________________________________________________________________________________________8

What happens to individual stars within colliding galaxies?There is so much space between it appears that little happens.

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What kind of galaxy is the Milky Way galaxy believed to be? _______________________________________The Milky Way galaxy measures about _____________ from one side to the other. The Sun lies about _________________from the galactic center on the edge of one of the spiral arms. The Milky Way’s disk is about ________________ thick.

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What kind of galaxy is the Milky Way galaxy believed to be? A spiral but might be a barred spiral galaxy. The Milky Way galaxy measures about 100,000 light-years from one side to the other. The Sun lies about 26,000 light-years from the galactic center on the edge of one of the spiral arms. The Milky Way’s disk is about 1,000 light-years thick.

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What are contained in the spiral arms of galaxies? ________________________________________________________________________

What do recent theories suggest may exist in the center of galaxies? ____

__________________________

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What are contained in the spiral arms of galaxies? The arms contain both young stars and prestellar material, such as glowing nebulae.

What do recent theories suggest may exist in the center of galaxies? Extremely massive black holes might exist at the cores of galaxies.

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Section CheckSection Check

Question 1

Which is NOT a type of galaxy?

A. ellipticalB. irregularC. roundD. spiral

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Section CheckSection Check

Answer

The answer is C. “Round” is not recognized as a major type of galaxy.

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Question 2

How do galaxies grow?

A. by producing new starsB. by emitting lightC. by absorbing other galaxiesD. by absorbing stars that don’t belong to other galaxies

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Answer

The answer is C. The Milky Way has been gobbling up the Sagittarius dwarf elliptical galaxy for 2 billion years.

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Question 3

Where is the Sun located in the Milky Way galaxy?

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A. at the center of the galaxyB. at the edge of one of the spiral armsC. 100,000 light-years from the center D. 1,000 light-years from the center

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Section CheckSection Check

Answer

The answer is B. The Sun lies about 26,000 light-years from the center of the galaxy on the edge of one of the spiral arms.

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