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Astro 1
Section 1
Professor Brandt
Wednesday
February 17th
1999
Announcements:
Lecture notes:
Class 17
Review for Quiz 2
What to expect?
-50 questions
multiple choice
scan sheets.
Emphasis is on material from class
but you are also responsible for
book material.
Main topics
not details.
Constellations - will review - also in back of book
and on professor's
course page
Simple math questions - E=mc2
HR diagram
No makeups unless official excuse.
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Ursa Major
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Ursa Minor
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Bootes
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Lyra
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Cepheus
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Hercules
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Cygnus
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Cassopeia
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Pegasus
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Andromeda
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Orion
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Polaris
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Arcturus
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Vega
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Betelgeuse
Rigel
The sun - spectral class G
Why does it shine?
Fusion reactions in core.
H->He
proton proton chain.
Layers of Sun
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core
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radiation zone
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convective zone
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photosphere
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chromosphere
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corona
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solar wind
Weather on surface of Sun
Granulation - USA size
bubbles from convection
zone.
Sunspots - Earth size
not black or cold.
Live for 1-5 weeks
B fields
Prominences - hot gas ejected from surface
riding
magneticfield
Flares - giant explosions from B field shearing.
Last 4 hours. 100 million H bombs. Near sunspots.
Solar rotation - differential
27 days at equator. 31 at poles.
Sunspot cycle - number of spots reaches a maximum every 11 years.
Not perfect clock. Also spots move toward equator as cycle progresses.
Part of 22 year solar cycle. 1645-1715 Little IceAge.
How sun affects people
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allows life on Earth
photosynthesis
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sunburns and skin cancer
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climate connections
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solar flares cause power outages sometimes
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Auorae - Northern Lights
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Will destroy Earth in about 5 billion years.
Why doesn't sun kill us? X/gamma rays made in core
but only
optical gets out.
E=mc2
E has units of ergs
m has units of grams
c = 3x1010 cm/s = speed of light
Say you converted 1 gram into pure energy
E = (1) (3x1010)(3x1010)
=9x1020 ergs
How stars behave along main sequence
As you increase the mass of a main sequence star
what happens to
the?
luminosity -- goes up
surface temperature -- goes up
color -- bluer
radius -- larger
lifetime -- shorter
OBAFGKM
Inverse square law for apparent brightness - the apparent brightness
of an object depends on the inverse square of its
distance.
How do we learn temperature of stars?
Use spectroscope to measure continuous radiation
Absorption lines - fingerprint pattern
How do we learn temperature of stars?
binary star systems - about 1/2 of all stars in
some can get mass using Newton's Law of gravity.
Which will appear brightest if all are at the same distance?
(A) main sequence star with temperature 10
000K
(B) 1 solar mass main sequence star
(C) white dwarf
Answer = A
Life cycle of "low mass" star = 1M(.)
Protostar = 30 million yr collapse
Main sequence H-> He - 10 billion yr
Orange and Red giant
H runs out in core. H->He in shell.
He ignites.
Planetary nebula
White dwarf
Black dwarf
Carbon never burns.
Life cycle of "high mass" star -- 15 M(.)
protostar
main sequence
He core with H shell burning
He ignites in core
H burning shell
C core
He shell burning
H burning shell
C ignites at 600 million K
O ignites
Ne ignites
Mg ignites
Si ignites
Iron Catastrophe.
Collapse and supernova
Neutron star and supernova remnant or black hole
6 supernovae in our galaxy in past 1000 years.
Pulsars - ice skater analogy. Magnetized
rapidly rotating neutron
stars.
X-ray binaries - accretion process. Accretion disk
Black holes
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