Download Layers of the Sun Test 1 study guide. Intoduction to Stars

Proton-proton
cycle
3 steps
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4 Layers of the Sun
CORE : center, where fusion occurs
RADIATION: energy transfer by radiation
CONVECTION: energy transfer by convection
PHOTOSPHERE: what we see
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Layers of the Sun
• Mostly Hydrogen with about 25% Helium. Small amounts of
heavier elements
• Gas described by Temperature, Pressure, and Density with P=
kDT (mostly)
• Larger temperature near Radius = 0
• Inner radius is a PLASMA - gas where all atoms are ionized.
T >100,000 degrees K – and so “free” electrons
H (48)
He (4)
electron
(56)
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Equilibrium
Temperature of the Sun is constant for any given
radius. It doesn’t change as heat flows out
Gravitational Force pulling in BALANCES the gas
pressure (Electric force) pushing out
At center : highest gravitational pressure gives the
highest temperature
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Temp is highest in the
core  where nuclear
fusion occurs
Convection Zone T =
6,000 – 100,000 K
heat flows outward to
surface, then radiated
as light to (say) Earth
Radiation Zone T =
100,000 – 5,000,000 K
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Core - Center of Sun
• High temperature ~15,000,000 degrees K
• high density ~ 100 g/cm3
• where fusion occurs
H 
He
and heat flows out
• source of neutrinos
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Core - changes with time
• As heavier, Helium produced by fusion reaction
tends to “float” to the center.
• For now, He isn’t burning and there is a mini-core of
(mostly) He with reduced fusion being built up
Red=H
green=He
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Radiation Layer
• temperature 100,000 to 5,000,000 degrees (plasma)
• no fusion
• electrons are not in atoms very, very opaque
• Energy transferred by absorption and reradiation of light
photon
photon
photon
electron
electron
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Convection Layer
• temperature 6,000 to 100,000 degrees
• no fusion
• electrons in atoms  less opaque
• Energy transferred through convection. Movement
of gas to/from surface (“hot” air rises)
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Convection and Radiation layers differ on how heat is transferred
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Photosphere
• Sun  gas cloud  no true surface
Light we see comes from a 200 km fairly
transparent region  photosphere and top of
convection region
•
temperature 4,500-6,000
• photosphere cooler than convection region
 dark line absorption spectrum
photosphere
Convection region
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Outer Atmosphere
• Surface of the Sun  hot, turbulent with electric/magnetic
storms which throw out energetic particles
• CHROMOSPHERE
low density, high T
glows red (H atom)  seen in eclipse
• CORONA
even lower density and higher T (over 1,000,000 degrees)
• SOLAR WIND
protons escaping Sun’s gravity so large velocity. Can interact
in Earth’s atmosphere
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Sunspots
• Intense magnetic fields which inhibited convection currents to the
surface  appear darker as at lower temperature
• Solar storms/flares often associated with sunspots
• Had been observed prior to Galileo’s time (and without telescopes)
– Galileo gets credit as he had best explanation
• Sunspot activity varies with time. 11 year cycle plus variation over
hundreds (thousands) of years – change in Solar energy output
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Outer Atmosphere
• Can see during eclipses. Interactions of solar wind
with Earth’s magnetic field and atmosphere causes
Aurora Borealis
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Aurora Borealis – Northern Lights
seen at high latitudes as magnetic fields are lower in the atmosphere.
rarely seen in DeKalb. Photos are from Alaska and Maine
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Solar Storms
• Large eruptions from Sun’s surface are called “flares” or
“storms”
• Will increase flow of charged particles to Earth, increase
Northern Lights, and have (some) radiation impact (plane
flights, on space station, radio signals)
• Large one in January 2012
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Test 1 Guide for short answer questions
• Motion of Sun, stars, planets through sky vs seasons
• Galileo’s astronomical observations
• Kepler’s Laws of planetary motion
• Newton’s Laws of motion apply to Kepler’s (mostly
F=ma)
• how light is produced (accelerated charge) plus
discrete vs. continuous
• nuclear reactions in the Sun : p-p cycle
• Layers in the Sun
• 4 forces with examples
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The Nature of Stars
• Measure properties of Stars
Distance
Mass
Absolute Brightness
Surface Temperature
Radius
• Find that some are related
Large Mass  Large Brightness
• Determine model of stellar formation and life cycle
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Distances to Stars
• Important as determines actual brightness but hard to
measure as stars are so far away
Closest Alpha Centauri
4.3 light years = 4 x 1013 km
(1 AU = distance Earth to Sun = 8 light minutes)
• Close stars use stellar parallax (heliocentric parallax or
triangulation  same meaning)
• Can “easily” measure distance using parallax to a few
100 LY. Need telescope: first observed in 1838. Study
close stars in detail. Other techniques for distant stars
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Distances to Stars - Parallax
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Shifting Star Positions
•
•
•
•
The orbit of the earth is used as the base.
Near stars appear to move more than far stars
distance = (base length)/angle
define: 1 parsec = 1/(angle of 1 second of arc) = 3.3 LY
site A
December
angle
Sun
site B
June
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Stellar Parallax
• A photo of the stars will show the shift.
July
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Nearest Stars
61 Cygni
first
parallax
in 1838
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Nearest Stars
•The larger the angle (T.Par. =
trigonometric parallax) the
closer the star
• many stars come in groups like
the 2 stars in the Sirius “binary
cluster”  close together,
within same “solar system”
•Alpha Centauri and Procyon
are close binary systems
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Parallax Data
• 200 BC, Hipparcos 850 stars, 1 degree; 1627, Brahe,
1000 stars, 1 arc-minute; 1725 (telescope) 3000 stars, 10
arc-seconds In 1900 only 60 stars had parallax
measurements. photographic plates  0.01 arc-seconds
• 1997-2000 European satellite Hipparcos parallax
measurements > 2,300,000 stars up to 500 LY distance
 118,000 stars .001 arc-second resolution
• OLD(1990): 100 stars with distance known to 5%.
“NEW” (2005): 7000 such stars
• ESA Gaia satellite: 2013 0.00001 arc-second. Goal:
measure 1 billion stars (2016 still analyzing)
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