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This Lecture Brought to You in Comic Sans MS
“With equal passion I have sought knowledge. I have
wished to understand the hearts of [people]. I have
wished to know why the stars shine.” -Bertrand Russell
Quotes
"One of the most impressive discoveries was the origin
of the energy of the stars. One of the men who
discovered this was out with his girl friend the night
after he realized that nuclear reactions must be going
on in the stars in order to make them shine.
She said "Look at how pretty the stars shine!"
He said, "Yes, and right now I am the only man in the
world who knows why they shine."
She merely laughed at him. Well, it is sad to be alone,
but that is the way it is in this world.“ - Richard Feynman, "The
Feynman Lectures“
“A star shines on the hour of our meeting.” - Elvish
greeting, "The Lord of the Rings“
“I wonder why. I wonder why. I wonder why I wonder.
I wonder why I wonder why I wonder.” - Richard Feynman
Readings: ASTRONOMY TODAY
Chapter 16 (excepting section 16.6)
Chapter 17 (without exception)
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General Solar Properties
Solar Properties
Percentage of Solar System Mass
Maximum Earth Distance (Km)
152,100,000
Minimum Earth Distance (Km)
147,100,000
Mean Distance from Earth (Km)
149,597,892
Earth Masses
333,400
Mass x10(30) (Kg)
1.99
Diameter of Photosphere (Earth = 1)
109.3
Diameter of Photosphere (Km)
Sol
ar
Pro
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99.80
1,390,000
Mean Density (g/cm(3))
1.41
Solar Constant (W/m(2))
1370
Luminosity x10(26) Watts
3.8
Spectral Class
G2 V
Effective Temperature (Kelvin)
5800
Apparent Magnitude
-26.7
Absolute Magnitude
4.8
Rotational Period at Equator
24d16h
Rotational Period at 40°
28d
Rotational Period at 80°
36d
Inclination to Equator to Elliptic
7°10'.5
Surface Gravity (Earth=1)
27.9
Surface Gravity m/s(2)
273
Average Sunspot Maxima (Yr.)
11.1
Average Magnetic Cycle (Yr.)
22.2
Average Escape Time for Photons
Orgininating in the Core (Yr.)
10,000
h
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Why does the sun shine?
•Chemical Burning – insufficient radiation
•Radiative Cooling – only thousands of years
•Gravitational Contraction – only 25 million years
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Stars convert energy into matter.
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600 million tons of
H
-> 598 million tons of
IN ONE SECOND
He
Basic Solar Structure
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The force of gravity inward and the radiation pressure
outward balance each other out.
Gravitational Equilibrium
Spectroscopy
Visible Spectrum
Sp
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91.2% Hydrogen – 8.7% Helium
0.1% Heavier Elements
Luminosity
The total power output of the sun: 3.8x1024 watts!!!
Think of your 60 watt light bulb.
1 second of the earth luminosity contains enough energy to
meet our needs for roughly 500,000 years!
Only about one two-billionth of that reaches Earth.
L
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Sun Spots
Not at all dark
Roughly the size of the earth
Show the differences in rotation: 27 days equator – 31 days poles
Only about one two-billionth of that reaches Earth.
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Granularity of the Solar Surface
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A Solar Prominence
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Solar Flare
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Understanding the sun:
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NEXT TIME:
End
Measuring the Stars