Download Finish up Sun and begin Stars of the Sun Test 1 Study

PHYS 162
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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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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
PHYS 162
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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
PHYS 162
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Test 1 Guide for short answer questions
• Motion of Sun, stars, and planets through sky vs season
• Galileo’s astronomical observations
• Kepler’s Laws of planetary motion
• Newton’s Laws of motion (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
PHYS 162
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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
• Gives model of stellar formation and life cycle
PHYS 162
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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 (later) for distant
stars
PHYS 162
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Distances to Stars - Parallax
PHYS 162
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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
PHYS 162
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Nearest Stars
61 Cygni first
parallax in 1838
Alpha Centauri
Sirius
Procyon
61 Cygni
Epsilon Indi
All binaries
Tau Ceti 12 LY
closest single “Sunlike” star
Epsilon Eridani
single - youngish
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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.
Proxima Centauri is a red dwarf
which probably orbits Alpha
Centauri every 500,000 years
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Nearest Stars
61 Cygni
first
parallax
in 1838
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Parallax Data
• In 1900 only 60 stars had parallax measurements
• 1997-2000 a European satellite Hipparcos released
parallax measurements for more than 2,300,000 stars
up to 500 LY distance
• 118,000 stars measured with .001 arc-second
resolution and 0.2% error on light intensity
• 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 objects ~70 times each over 5 years
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Luminosity of Stars
• Luminosity=Absolute Brightness=how
much light/energy a star produces
• Scale relative to Sun. So
Lsirius = 23LS means Sirius radiates 23 times
more energy than the Sun
• Stars range from .0001xLS to 1,000,000xLS
Another scale: “magnitude” often used. A log scale to
the power of ~2.5. YOU DON’T NEED TO KNOW.
The lower the Mag the brighter the object
PHYS 162
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Absolute vs Apparent Brightness
Absolute Brightness/Luminosity means total energy output
Apparent Brightness is what is seen by eye or in a
telescope and so depends on distance (1/Distance2)
PHYS 162
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Absolute vs Apparent Brightness
Example: 2 stars with the same absolute brightness
Star(A) is 3 times further away from us then Star(B)
therefore the apparent brightness of Star(A) is 1/9 that
of Star(B)
90 LY
30 LY
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apparent brightness what
we see
magnitude scale
close to us
far away
but very
large
Absolute
brightness
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Brightness: Sirius vs Rigel
• Sirius is 23 times as bright as our Sun
Rigel is 30,000 times as bright as our Sun
• Sirius is 8.6 light years from us
Rigel is 30,000 light years from us
• Which star looks brighter in the sky? Has the
larger apparent luminosity?  Sirius
Sirius :
Rigel :
23
23

 0.3
2
8.6
74
30000
30000

 0.07
2
680
460000
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Binary Star Systems
• Many stars come in groups of 2 or 3 that are close
(few AU) to each other: BINARY Star Systems
• Gravitationally bound and probably formed at the
same time
• SiriusA is 23 times as bright as our Sun
SiriusB is 0.005 times as bright as the Sun
Their separation varies from 8 to 31 AU
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Binary Stars  Stellar Masses
• visually observe both stars  Visual Binary.
If only separate into 2 stars by looking at the
spectrum  Spectroscopic Binary (eclipse each
other plus have different Doppler shifts)
• Measure orbital information  period and
separation distance. Get Mass though
Kepler/Newtonian-like methods
PHYS 162
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Binary Star Orbits - Eclipses
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Binary Star Orbits – Doppler Shifts
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Extra Slides
PHYS 162
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Weak Nuclear Force
• Affects all particles (except photon)
• Weaker than electromagnetic force except at high
energies where the same strength
• Short range - size of proton
• Causes changes in particle type. Many radioactive
decays are “weak” and so can occur slowly
proton
neutron
electron
neutrino
particle
PHYS 162
antiparticle
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Neutrinos - little neutral ones
• Postulated to exist in 1930s, discovered in 1956 (second
type discovered in 1962). Neutrinos (n) have:
almost 0 mass and no electric charge
unaffected by strong nuclear force
 only interact by weak nuclear force
• only 1 of 1010 produced in the Sun’s interior interact in
Sun’s outer layers  can be used to study Sun’s interior
Sun
n
PHYS 162
Earth
detector >1000
tons of water
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