galaxies and the milky way. attendance quiz are you here today? (a) yes (b) no (c) to infinity…and...

Galaxies and

The Milky Way

Galaxies and

The Milky Way

Attendance Quiz

Are you here today?

(a) yes

(b) no

(c) To infinity…and beyond!

Here!

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are needed to see this picture.

Reminder about the studyReminder about the study• The e-mails for the first two post-instruction inventories

containing the links (URL) were sent Monday

• You have until next Monday at 9am to complete them

• None of the inventories will be graded. However, you will get course credit (10 clicker points or about 2% of your total course grade) for completing all eight inventories

• If you complete only the pre- and post-instruction versions of the Light and Spectroscopy Concept Inventory (a total of two inventories) you will still receive 5 clicker points

• You should not study for them, or use any outside resources. The idea is to measure how much the class has influenced what you know and think about science (astronomy in particular)

• The e-mails for the first two post-instruction inventories containing the links (URL) were sent Monday

• You have until next Monday at 9am to complete them

• None of the inventories will be graded. However, you will get course credit (10 clicker points or about 2% of your total course grade) for completing all eight inventories

• If you complete only the pre- and post-instruction versions of the Light and Spectroscopy Concept Inventory (a total of two inventories) you will still receive 5 clicker points

• You should not study for them, or use any outside resources. The idea is to measure how much the class has influenced what you know and think about science (astronomy in particular)

Today’s TopicsToday’s Topics• Galaxy types

• Spiral• Elliptical• Irregular

• Hubble’s classification scheme

• Structure of the Milky Way

• Galaxy types• Spiral• Elliptical• Irregular

• Hubble’s classification scheme

• Structure of the Milky Way

Hubble Ultra Deep Field (11.3 day exposure)Hubble Ultra Deep Field (11.3 day exposure)• Between September 3, 2003 and

January 16, 2004, the Hubble Space Telescope stared at a single, seemingly empty patch of sky in the constellation Fornax

• This observation lasted for 1,000,000 seconds, or about 11.3 days

• The resulting image was the deepest ever taken by a telescope, and covered a patch of sky only 1/100th the size of a full moon

• It revealed over 10,000 objects, most of which are galaxies

• Between September 3, 2003 and January 16, 2004, the Hubble Space Telescope stared at a single, seemingly empty patch of sky in the constellation Fornax

• This observation lasted for 1,000,000 seconds, or about 11.3 days

• The resulting image was the deepest ever taken by a telescope, and covered a patch of sky only 1/100th the size of a full moon

• It revealed over 10,000 objects, most of which are galaxies

Hubble Ultra Deep Field (10,000 galaxies)Hubble Ultra Deep Field (10,000 galaxies)

The Beginning of TimeThe Beginning of Time• As we look at distant galaxies, we are looking back in time, due to the finite speed of light

• Thus, when we see a galaxy 13 billion light years away, we are seeing it as it was 13 billion years ago

• Since the expansion rate of the universe tells us the universe is about 14 billion years old, we are seeing these galaxies very early in the history of the universe

• As we look at distant galaxies, we are looking back in time, due to the finite speed of light

• Thus, when we see a galaxy 13 billion light years away, we are seeing it as it was 13 billion years ago

• Since the expansion rate of the universe tells us the universe is about 14 billion years old, we are seeing these galaxies very early in the history of the universe

Types of GalaxiesTypes of Galaxies• Galaxies fall into 3 main categories

• Spiral Galaxies - flat white disks with yellowish bulges at their center.

These disks contain gas and dust, and show spiral arms, where SF is occuring• Elliptical Galaxies - redder, ellipsoidal collections of stars with varying degrees of

flatness (some spherical, others football shaped)• Irregular Galaxies - no coherent structure; may be the result of a galaxy collision or

other gravitational interaction with a nearby galaxy

• Galaxies fall into 3 main categories• Spiral Galaxies - flat white disks with yellowish bulges at their center.

These disks contain gas and dust, and show spiral arms, where SF is occuring• Elliptical Galaxies - redder, ellipsoidal collections of stars with varying degrees of

flatness (some spherical, others football shaped)• Irregular Galaxies - no coherent structure; may be the result of a galaxy collision or

other gravitational interaction with a nearby galaxy

Hubble’s Classification SchemeHubble’s Classification Scheme• Each galaxy is assigned a letter - E=elliptical, S=spiral, Irr=irregular• Ellipticals are given a number to describe their roundness (0=spherical)• Spirals are given a capital B if they are barred, and a letter a-c

a = tight spiral arms, large bulge, little dust in the disk

c = loose spiral arms, small bulge, lots of dust in the disk

• Each galaxy is assigned a letter - E=elliptical, S=spiral, Irr=irregular• Ellipticals are given a number to describe their roundness (0=spherical)• Spirals are given a capital B if they are barred, and a letter a-c

a = tight spiral arms, large bulge, little dust in the disk

c = loose spiral arms, small bulge, lots of dust in the disk

Hubble’s Classification SchemeHubble’s Classification Scheme• Hubble (and others) thought this classification scheme might be an

evolutionary sequence• However, the existence of all types of galaxies together at all times, as far

back in time as we look (by looking further away), makes this unlikely (click for image)

• Hubble (and others) thought this classification scheme might be an evolutionary sequence

• However, the existence of all types of galaxies together at all times, as far back in time as we look (by looking further away), makes this unlikely (click for image)

Lecture Tutorial: Galaxy Classification, pp. 127-130

Lecture Tutorial: Galaxy Classification, pp. 127-130

• Work with one or more partners - not alone!

• Get right to work - you have 15 minutes

• Read the instructions and questions carefully.

• Discuss the concepts and your answers with one another. Take time to understand it now!!!!

• Come to a consensus answer you all agree on.

• Write clear explanations for your answers.

• If you get stuck or are not sure of your answer, ask another group.

• If you get really stuck or don’t understand what the Lecture Tutorial is asking, ask me for help.









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Galaxy CollisionsGalaxy Collisions• Galaxies form by collisions and

mergers

• Irregular galaxies are thought to be galaxies undergoing such mergers

• Shown here are a pair of galaxies merging called the “Antennae Galaxies”

• Giant Elliptical galaxies (10-100 times the size of the Milky Way) form by cannibalizing their neighbors over billions of years

• This movie shows that the fate of the Milky Way is to collide and merge with the Andromeda Galaxy

MW-Andromeda collision movie

• Galaxies form by collisions and mergers

• Irregular galaxies are thought to be galaxies undergoing such mergers

• Shown here are a pair of galaxies merging called the “Antennae Galaxies”

• Giant Elliptical galaxies (10-100 times the size of the Milky Way) form by cannibalizing their neighbors over billions of years

• This movie shows that the fate of the Milky Way is to collide and merge with the Andromeda Galaxy

MW-Andromeda collision movie

Many views of a galaxy collisionMany views of a galaxy collision

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Milky Way TopicsMilky Way Topics

• Structure of the Milky Way • Formation of the Milky Way • Difficulties of our position in the Milky Way

• Structure of the Milky Way • Formation of the Milky Way • Difficulties of our position in the Milky Way

Structure of the Milky WayStructure of the Milky Way• We now have a pretty clear idea of

the structure of our home galaxy• We live about halfway to the edge of

a highly flattened spiral galaxy

Interactive Figure 19.1

• Our galaxy is a typical spiral galaxy• Highly flattened disk (like a CD)

• Stars in this disk are in circular orbits• There are both old and young stars• These stars contain ~2% heavy

elements (heavier than He), like the Sun

• Roughly spherical bulge in the center• Halo of globular clusters and other

stars• Stars in the bulge/halo move in 3-D

elliptical orbits• All old stars with little or no heavy

elements

• We now have a pretty clear idea of the structure of our home galaxy

• We live about halfway to the edge of a highly flattened spiral galaxy


• Our galaxy is a typical spiral galaxy• Highly flattened disk (like a CD)

• Stars in this disk are in circular orbits• There are both old and young stars• These stars contain ~2% heavy

elements (heavier than He), like the Sun

• Roughly spherical bulge in the center• Halo of globular clusters and other

stars• Stars in the bulge/halo move in 3-D

elliptical orbits• All old stars with little or no heavy

elements

Not an actual photograph!

Difficulties of our position in the Milky WayDifficulties of our position in the Milky Way• Because we live in the plane of the galaxy, we have a very obscured picture of

things in the Milky Way• In particular, there is interstellar dust obscuring our view, particularly towards

the Galactic Center• Nonetheless, we can learn quite a lot, if we remain aware of our surroundings

• Because we live in the plane of the galaxy, we have a very obscured picture of things in the Milky Way

• In particular, there is interstellar dust obscuring our view, particularly towards the Galactic Center

• Nonetheless, we can learn quite a lot, if we remain aware of our surroundings

Our Position in the Milky Way Our Position in the Milky Way • In the late 1700s, William and Caroline Herschel (brother and sister)

mapped nearby stars and concluded that the Sun was near the center of a slightly flattened distribution of stars

• Later, more quantitative studies, in the early 1900s, showed that this distribution is about ~500 x 2500 light years in size

• Some astronomers were suspicious of this (remember Copernicus)• Q: What could make us think were were near the center of the Milky Way

when we aren’t?• A: Interstellar medium!

• In the late 1700s, William and Caroline Herschel (brother and sister) mapped nearby stars and concluded that the Sun was near the center of a slightly flattened distribution of stars

• Later, more quantitative studies, in the early 1900s, showed that this distribution is about ~500 x 2500 light years in size

• Some astronomers were suspicious of this (remember Copernicus)• Q: What could make us think were were near the center of the Milky Way

when we aren’t?• A: Interstellar medium!

This modern image of the Milky Way clearly shows the dark patches caused by interstellar dust, which is responsible for the pervasive dimming and obscuring of objects far from the Solar System

Our Position in the Milky Way Our Position in the Milky Way


• In the early 1900s, Harlow Shapley observed the distribution of globular clusters, and found that they were centered on a point 10s of thousands of light years from the Sun

• He also found that these clusters avoided the plane of the Milky Way

• From these facts, he concluded1. The Sun is not at the center of the Milky

Way

2. The Milky Way is much bigger than had been previously thought

• In the 1920s, Robert Trumpler, observing open clusters, demonstrated that there is an obscuring “fog” which makes distant objects seem dimmer than they should - like car headlights in a fog

• In the early 1900s, Harlow Shapley observed the distribution of globular clusters, and found that they were centered on a point 10s of thousands of light years from the Sun

• He also found that these clusters avoided the plane of the Milky Way

• From these facts, he concluded1. The Sun is not at the center of the Milky

Way

2. The Milky Way is much bigger than had been previously thought

• In the 1920s, Robert Trumpler, observing open clusters, demonstrated that there is an obscuring “fog” which makes distant objects seem dimmer than they should - like car headlights in a fog

Milky Way Quiz IMilky Way Quiz I

Why is it difficult to get a good picture of what ourMilky Way galaxy looks like?

a) We’re in the middle of one of its arms–no perspectiveb) It is very large and the edges are far away and faintc) Dust blocks our view when we look toward the center or

in the planed) No one has ever taken a photo from both the top and side

of ite) All of the above

Why is it difficult to get a good picture of what ourMilky Way galaxy looks like?

a) We’re in the middle of one of its arms–no perspectiveb) It is very large and the edges are far away and faintc) Dust blocks our view when we look toward the center or

in the planed) No one has ever taken a photo from both the top and side

of ite) All of the above

Milky Way Quiz IIMilky Way Quiz II

You observe two identical stars at the same distance. One is in the disk of the Milky Way, the other in a direction perpendicularly out of the disk. Chances are the disk star will be

a) brighter and be reddened by dust

b) less bright and be reddened by dust

c) brighter and be less reddened by dust

d) less bright and be less reddened by dust

You observe two identical stars at the same distance. One is in the disk of the Milky Way, the other in a direction perpendicularly out of the disk. Chances are the disk star will be

a) brighter and be reddened by dust

b) less bright and be reddened by dust

c) brighter and be less reddened by dust

d) less bright and be less reddened by dust

Lecture Tutorial: Milky Way Scales, pp. 123-125

Lecture Tutorial: Milky Way Scales, pp. 123-125

















Milky Way Quiz IIIMilky Way Quiz III

Where is our Sun located in the Milky Way Galaxy?

a) at the exact center

b) near the center

c) about half way between the center and the outer edge

d) near the outer edge

Where is our Sun located in the Milky Way Galaxy?

a) at the exact center

b) near the center

c) about half way between the center and the outer edge

d) near the outer edge

Milky Way Quiz IVMilky Way Quiz IV

Which letter represents M45 on the MW diagram (Q5)?

a) A

b) B

c) C

d) D

e) E


a) A

b) B

c) C

d) D

e) E

Milky Way Quiz VMilky Way Quiz V


a) A

b) B

c) C

d) D

e) E


a) A

b) B

c) C

d) D

e) E

Milky Way Quiz VMilky Way Quiz V

Does the Andromeda Galaxy fit on the diagram?

a) yes

b) no

Does the Andromeda Galaxy fit on the diagram?

a) yes

b) no

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