1755: Immanuel Kant

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1755 Immanuel Kant Distant Groups of Stars -
like the Milky Way Island Universes
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Another Idea Spiral Nebulae Nearby Stars in
Process of Forming
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Edwin Hubble 1925 - Trying to get distance to
Great Spiral Nebula in Andromeda Standard
Bulbs?
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M31 Andromeda
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900,000 lyr. away!
(actually 2.2 million lyr.)
M31 Andromeda
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HST - Deep Field North 10 Day Exposure Piece of
Sky Size of Grain of Sand at Arms Length
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HST - Deep Field North 10 Day Exposure 2500
Galaxies
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The Sombrero Galaxy Virgo
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M100 Coma Berenices
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Sa
Sb
Sc
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M83 Hydra
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NGC 1365 Fornax
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SBa
SBb
SBc
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Sa
SBa
Sb
SBb
Sc
SBc
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Spiral Galaxies in General Disks 20,000 -
100,000 lyr across Rotating Masses 109 - 1012
MSun All contain significant dark
matter Luminosities 108 - 1011 LSun
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Leo II Dwarf Elliptical
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Irregular Galaxies Chaotic appearance Often
seen with bursts of star formation Tend to be
lower mass Tend to be lower lumin. than spirals
M82 Ursa Major
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LMC 160,000 lyr away 45,000 lyr across Note star
formation!
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SMC 192,000 lyr away 35,000 lyr across
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Hubbles Tuning Fork Diagram An Evolutionary
Sequence?
No! Idea Galaxies form as one type stay that
way
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Ellipticals Little initial rotation Star
formation efficient Gas used fast before could
collapse into disk
Spirals Some initial rotation Star formation
NOT efficient Little gas used to make stars
before gas collapsed into disk
But This Cant Be All Of The Story!
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NGC 1322 S0 Galaxy
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M51 (NGC 5194/5195) The Whirlpool Nebula
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The Mice (NGC 4676)
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Andromeda/Milky Way Interaction Numerical
Simulation 5 Billion Years from Now
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The Perseus Galaxy Cluster
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M31 Andromeda
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M87 Virgo
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The Sombrero Galaxy Virgo
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Handy Way to Weigh Spirals MInside Orbit
D3/P2 (Pperiod, D distance from center) P
2pD/V (Pperiod, D distance from center, V
speed in orbit) MInside Orbit
D3/(2pD/V)2 So, MInside Orbit depends on V2 x D
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M85 Coma Berenices
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Hubbles Discovery of Cepheids in M31 (Andromeda
Galaxy) 350 exposures (several hours long
each) 18 years to find 40 Cepheid Variables
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M100 65 million lyr
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Possible Standard Bulbs
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Possible Standard Bulbs The Brightest Stars in
a Galaxy (65 mlyr) (wont work for ellipticals -
why?)
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Possible Standard Bulbs The Brightest Stars in
a Galaxy (65 mlyr) (wont work for ellipticals -
why?) Size of Planetary Nebula (70 mlyr)
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Possible Standard Bulbs The Brightest Stars in
a Galaxy (65 mlyr) (wont work for ellipticals -
why?) Size of Planetary Nebula (70 mlyr) Sizes
of Globular Clusters (100 mlyr)
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Possible Standard Bulbs The Brightest Stars in
a Galaxy (65 mlyr) (wont work for ellipticals -
why?) Size of Planetary Nebula (70 mlyr) Sizes
of Globular Clusters (100 mlyr) Type I
Supernovae (8,000 mlyr! really good - why?)
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Possible Standard Bulbs The Brightest Stars in
a Galaxy (65 mlyr) (wont work for ellipticals -
why?) Size of Planetary Nebula (70 mlyr) Sizes
of Globular Clusters (100 mlyr) Type I
Supernovae (8,000 mlyr! really good - why?) The
Brightest Galaxy in a Cluster (13,000 mlyr)
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Quiz 9
Just for fun, Dr. Briley assigns you a star in
the sky to study. He tells you where it is in the
sky and nothing else, but you can make any
observation of it possible with today's
equipment. How would you figure out whether it
was a Population I and Population II
object? Discuss what observations you would make
and how that observation would help classify the
population type of the star.
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