Download Chapter 14 Our Star The Sun is the Largest Object in the Solar

Chapter 14
Our Star
The Sun is the Largest Object
in the Solar System
• The Sun contains more than 99.85% of
the total mass of the solar system
• If you put all the planets in the solar
system, they would not fill up the volume
of the Sun
• 110 Earths or 10 Jupiters fit across the
diameter of the Sun
© 2006 Pearson Education Inc, publishing as Addison-Wesley
What makes the Sun shine?
• Nuclear (mass) energy makes the Sun
shine
E = mc2
Nuclear P.E.
Luminosity
= ~ 10 billion yrs
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3
Sun releases energy by fusing four hydrogen nuclei into one
helium nucleus
Sun releases energy by fusing four hydrogen nuclei into one
helium nucleus
extra
mass
Neutrons are less massive than protons
Total mass is 0.7% lower
Mass converted to energy: E = mc2
Neutrons are less massive than protons
Total mass is 0.7% lower
Mass converted to energy: E = mc2
© 2006 Pearson Education Inc, publishing as Addison-Wesley
© 2006 Pearson Education Inc, publishing as Addison-Wesley
What is the Sun’s structure?
The Stable Sun
Sun is in
• Gravitational Equilibrium:
✴ Pressure Out = Gravity In
• Thermal Equilibrium:
✴ Energy Out (radiated)
= Energy Produced (fusion)
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Radiative Zone
INTERIOR:
Radiative Diffusion: Energy
gradually leaks out of
radiation zone in form of
randomly absorbed/reemitted photons
The Sun’s interior
has three layers:
(1) core
(2) radiative zone
(3) convective
zone
Energy generated in the core of the Sun propagates outward
through these different layers, and finally, through the
atmosphere of the Sun. This process takes tens of thousands of
years or more.
© 2006 Pearson Education Inc, publishing as Addison-Wesley
Solar Vibrations
Convective Zone
• Hot gas becomes less dense;
rises
• Releases heat at surface;
cools; becomes less dense;
sinks
• “Helioseismology”
• Pressure waves (sound
waves) from moving gas
• Cause “vibrations” of
surface: detected from
doppler shift
• Waves change due to
changing T, density with
radius in Sun
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Patterns of
vibration on
surface tell us
about what Sun
is like inside
Solar Neutrinos
• Neutrinos created during fusion
fly directly through the Sun
• Observations of these solar
neutrinos can tell us what’s
happening in core
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© 2006 Pearson Education Inc, publishing as Addison-Wesley
© 2006 Pearson Education Inc, publishing as Addison-Wesley
Solar neutrino problem:
Early searches for solar
neutrinos failed to find
the predicted number
More recent
observations find the
right number of
neutrinos, but some
have changed form
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The Sun’s atmosphere also has three layers…
•
•
•
Photosphere the layer we see,
5800 K
Chromosphere the red layer
observed using a
hydrogen filter,
10,000 K
Corona - the
incredibly thin
outer
atmosphere,
1,000,000 K
Photosphere
Visible layer of the Sun
Granulation caused by convection
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Convective Cells in the Sun
Chromosphere:
Middle layer of
solar atmosphere
~ 104 - 105 K
Hot, thin gas:
emission line
spectrum (mostly
Hα
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Spicules
• Jets of hot gas extending a few 1000 km
up; fall back
Corona:
Outermost layer
of solar
atmosphere
~1 million K
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The corona, the outermost part of the Sun’s
atmosphere, is characterized by its high
temperature and low density
Solar wind:
A flow of charged
particles from the
surface of the Sun
The Sun also
ejects a stream
of charged
particles into
space known
as the solar
wind
© 2006 Pearson Education Inc, publishing as Addison-Wesley
Sunspots
The annual change in numbers of sunspots reveals that
the Sun experiences an 11-year Sun Spot cycle
Are cooler (4000 K) than other parts of
the Sun’s surface (6000 K)
Maximum
number
Minimum
number
Are regions with strong magnetic fields
Stars and their Properties
Measuring Distances
• Use parallax
to measure
distances to
(nearby)
stars
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The Magnitude Scale
Apparent
Magnitude is a
number that represents
the apparent brightness
of stars as seen on Earth
How bright a star appears depends on both how much light it
releases (its actual brightness or luminosity) and how far away it is
(distance) according to the inverse square law
Apparent Brightness =
Luminosity: L
The LARGER the number the
dimmer the object will appear
from Earth
L
Surface Area
=
L
4πd2
Surface Area: 4πd2
Note we use the letter “m”
for apparent magnitude
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True Brightness (Luminosity)
If you pass white light through a prism, it
separates into its component colors.
long wavelengths
• Dim stars are common
• Luminous stars are rare
R
O
Y
G
B
I
V
short wavelengths
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spectrum
Spectra
Three Stars: Different Temperatures
A
B
C
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Stars are classified by their spectra as
O, B, A, F, G, K, and M spectral types
O
B
A
F
G
K
M
Hot
(25,000 K)
Cool
(3500K)
This is a TEMPERATURE sequence
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Stars are classified by their spectra as
O, B, A, F, G, K, and M spectral types
•
•
•
•
OBAFGKM
hottest (>25,000 K) to coolest (3500 K)
bluish to reddish
An important sequence to remember:
– Oh Be a Fine Guy (or Girl), Kiss Me
– Oh Boy, An F Grade Kills Me
The Hertzsprung-Russell
(H-R) diagram identifies
a definite relationship
between temperature and
absolute magnitude
• Main Sequence
stars are found in
a band from the
upper left (hot,
bright) to the
lower right (cool,
dim)
• 90% of stars are
in this stage of
their lives
• Includes our sun
HR DIAGRAM
Large radius
• Stars fall into one
of 4 groups
(based on L, T
relation)
–Main Sequence
–Supergiants
–Giants
–White Dwarfs
Small radius
© 2006 Pearson Education Inc, publishing as Addison-Wesley