extra credit!
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Extra credit!. Get out your clickers. The following questions are worth 2 points each. What direction does the Sun rise in Sydney?. In the East In the West In the North In the South Cannot conclude. Looking south in Sydney, what type of stars would you see?. Seasonal Circumpolar - PowerPoint PPT PresentationTRANSCRIPT
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Extra credit!
Get out your clickers.
The following questions are worth 2 points each.
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What direction does the Sun rise in Sydney?
A. In the East
B. In the West
C. In the North
D. In the South
E. Cannot conclude
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Looking south in Sydney, what type of stars would you see?
A. Seasonal
B. Circumpolar
C. Neither
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Looking North in Sydney, what type of stars would you see?
A. Seasonal
B. Circumpolar
C. neither
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Sydney’s circumpolar stars rotate
A. Counterclockwise
B. Clockwise
C. Rise in east, set in west
D. Rise in west, set in east
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Agenda
Reading: Finish Unit 5, if you haven’t already.
Star clusters Stellar life cycles (stellar evolution)
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Star clusters
Easier to observe overall evolution than of one star
Stars in a cluster Formed at the same time Have similar composition They will differ only in mass
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Globular clusterM 15
NASA
Thousands to millionsof stars
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Globular cluster Tucanae 47
NASA
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Open cluster: Pleiades
Hundreds of stars
Case Western
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Open Cluster: Jewel box
Jordell Observatory
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HR diagram of a cluster
Color (B – V) on horizontal axis Equivalent to
OBAFGKM Apparent magnitude
(V) on vertical axis All stars at the same
distance Easy to convert to
absolute magnitude
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Evolution and the HR diagram
High mass (higher luminosity) stars progress through life more quickly
Lower mass stars take longer to be born, consume their fuel more slowly.
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Which HR diagram shows the older cluster?
A. B.
C. Cannot conclude
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Young cluster ~80 million yrs
U. of Sheffield
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Older cluster
U. of Oregon
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Compare the HR diagrams
Many older red giantsMany young, hot (blue) stars
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Star clusters — summary
Stars in one cluster are of different types but the same age.
Observing many clusters tells us about star life cycles HR diagram Old stars leave the main sequence Cluster age <=> turnoff point
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Stellar “evolution” (first part)
What we found in star clusters: Small stars live longer Very massive stars live hard and die
young Old stars leave the main sequence to
become red giants.
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Raw materials for star birth
Interstellar clouds.
This is a star cluster in the making!
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Raw materials for star birth
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In a Stellar nursery
Raw materials collapse Protostar begins to spin Eventually, fusion of H into He begins
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Life as a star
Zero-age main sequence when a star first starts fusing H into He
Stars do this for 90% of their lives
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Big stars don’t live long!
Massive stars burn very fast.
They soon run out of fuel!
Wikipedia
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Time on main sequence versus initial stellar mass
0.4 0.8 1.1 1.7 3.3 16 40
Large stars live and die very quickly!200 billion years!
Initial stellar mass (MSun)
~12 billion years (Sun)
50 million years
1 million years!
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He core contracting
H fusing
Exterior expanding
H runs out: star becomes a red giant
This is how starsleave the main sequence!
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Wikipedia
Our star is tiny comparedto a red giant!
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Further evolution
Helium all used up, gravity takes over again
Much mass is spewed into space
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Mass now determines death
Low mass: White dwarf Medium mass: Neutron star or pulsar High mass: Black hole
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Summary
Stars are born from Hydrogen Stars spend 90% of their lifetime
fusing Hydrogen into Helium Stars leave the main sequence and
become red giants
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Next time
Death of stars:
Black holes, neutron stars, Relativity