The Sun
1. Vital Statistics:
A. Diameter – 865,000 miles
B. Color – Yellow
C. Apparent Magnitude - -26.5
D. Absolute Magnitude - +4.7
E. Period of Rotation – About 35 days at the poles and
25 days at the equator
F. Density – 1.41 G/cm3 (About the Same as the Gas Planets)
G. Mass – Earth = 1 , Sun = 332,000
H. Surface Gravity – 275 m/second2
I. Escape Speed – 618 km/second
J. Surface Temperature – 12,000 degrees Fahrenheit
Hot enough to melt any known substance
K. Composition- 76 % Hydrogen, 22% Helium, and
About 2 % heavy elements (Very similar to Gas Giants)
Jupiter
Earth
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2. Sun’s Energy-
A. Suns’ Energy is generated by Nuclear Fusion
- Nuclear Fusion is when the Atoms lighter elements
combine to form new heavier Elements.
- In the process Electromagnetic Energy (Visible
light, UV light, X-rays, Gamma rays) is released.
- On Earth, fire also generates heat and other electromagnetic energy but
fire involves the electrons of atoms only and occurs under relatively cool
conditions.
- In the Sun’s core the pressure and temperature are so high that it
causes hydrogen molecules to move at 300 miles per second. At this
speed when they hit each other, they fuse together.
-In the core of the Sun, Hydrogen is being fused to
make Helium This Process is called Hydrogen
“Burning”
So Where does the Energy come from?
2. Sun’s Energy (cont.)
- Hydrogen has an atomic Mass of 1.0079
- Helium (Takes 4 Hydrogen’s to make a Helium) has an atomic mass of
4.00260
- However 1.0079 X 4 equals 4.0316 ????
- Einstein’ Law of conservation of Mass and Energy states that neither
Mass nor Energy can be created or destroyed….It just changes form.
Therefore the difference in the mass must have become energy E=MC2
since there are a lot of hydrogen atoms and the speed of light is so
large….even tiny amounts of mass become LOTS of Energy
- Every second the sun produces the equivalent amount of energy created
by 100 billion one megaton bombs
- * Six seconds of direct solar energy would evaporate all the Earth’s
oceans
- * Three minutes would melt the Earth’s crust
Hydrogen Fusion (How our Sun makes Energy)
3. Sun’s structure-
A. Hydrostatic Equilibrium- Balance between the forces
holding the Sun together (Gravity) and the Forces
trying to rip the Sun Apart (Nuclear Fusion
Explosions)
B. Core-
- The innermost 10% of the Sun
- Nuclear Fusion occurs in this layer
- Temperature of about 27 million degrees F and about 20 times denser
than iron. (However still a gas due to extreme temps)
3. Sun’s structure (cont.)
C. Radiative Zone-
- 85% of the internal mass of the Sun
- Energy is transported by Radiation ( in energy waves)
from the super hot interior to the cooler exterior. (This is
where gamma waves change to visible light rays. Takes about a million
years for a single photon to reach the surface from the core)
D. Convection Zone-
-Outer 15 % of the Suns’ Radius
- Energy is transported by bulk motions of gas called Convection
- Convection causes hotter areas of gas to rise to the
surface and cooler areas to sink down into lower layers.
3. Sun’s structure(cont.)
E. Photosphere- The visible “surface” of the Sun
- The layer at which the density of gas
becomes visible enough for us to see – Very
narrow layer
-”Edge” of the Sun is so sharp because of the quick transition
from visibility of gases to transparency of solar atmosphere.
- Atoms in this layer are constantly absorbing radiation from the
hot interior.
- Sunspots, Solar Flares, and Solar
Prominences are formed in this layer (We will
revisit these in a bit)
Sunspots
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3. Sun’s structure-
F. Solar Atmosphere-
- Extremely low density gases that lie above the photosphere, consists of two
main regions:
- 1. Chromosphere-
- Pink glowing region of gas just above the
photosphere
- Temperature of about 20,000 degrees F (Hot)
- Can be seen by the naked eye only during a solar eclipse
- Spicules- spikes of glowing gas probably due to magnetic
changes
2. Corona –
- Above Chromosphere – Temperature of about 3 million F
-Layer of extremely hot ionized glowing transparent
gas (Heat thought to come from Interactions between gas and
Magnetic Field – But not sure)
- Only visible during an eclipse or by viewing through a
coronagraph (Machine that artificially eclipses the Sun) due to
transparency of gas.
3. Sun’s structure-
G. Solar Wind:
- Because of very high temps its own atoms
are actually able to escape the Sun’s gravity.
- The mass lost is called the Solar Wind and
consists mainly of electrons and atoms of hydrogen and helium.
- Heliopause- Outer Boundary of the Solar
Wind at a distance of about 50 AU (5 Billion Miles) from the
sun
Suns’ Chromosphere
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Spicules
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Sun’s
Photosphere
surrounded by
Corona
Sun’s Corona as seen through an Eclipse
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Very Active Corona- Photo taken
during 1991 July Eclipse
Coronal Mass Ejections- due to very high temps of corona,
large amounts of solar material escape into space. Photo
taken with a coronagraph
4. Sun’s Important Features
A. Sunspots- a magnetically disturbed region of the
photosphere that is cooler than its surroundings.
- Appears dark only because its gases are a few thousand degrees
cooler than surround gas….so it radiates less energy.
- May appear as single sunspots or in groups
- There seems to be about an 11 year cycle from solar minimum
to maximum back to minimum
1. Cause-
- due to differential rotation of Sun, the Magnetosphere sometimes
develops coils and eventually kinks, which dramatically increase the
strength of the field.
- The strong magnetic field probably inhibits convection and thus
prevents heated gas from rising up to the surface.
- Eventually field collapses and resets itself to start a new cycle
Sunspot with Umbra at Center, surrounded by Penumbra
27
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Sunspot Cycle over the Last 150 Years
Low Sunspot Activity which Coincided with
Unusually cool Climate on Earth
Process of Sunspot Formation – Differential Spin
rate of Sun causes the magnetic field to coil.
Eventually wraps coils so tight that they kink and
penetrate the photosphere.
How Sunspots form
Magnetic Field disrupts convection currents and prevents
hot gases from rising up into photosphere 34
Sunspots Always
seem to occur in
pairs. Probable due
to how the kinks in
Magnetic field
penetrate the
photosphere
4. Sun’s Important Features (cont.)
B. Solar Prominences-
- Huge plumes of glowing gas that erupt from
disturbed regions of sunspots. They can be
observed on the edge of the sun.
Solar Prominence as observed from the edge of
the Sun
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Unusually Large
Solar Prominence
as viewed by SOHO
spacecraft in 1999
4. Sun’s Important Features (cont.)
C. Solar Flares- Gigantic Outbursts of Charged particles
as well as Visible, UV, and X-rays created when
extremely hot gas that spouts upward from the
surface of the sun.
-Usually associated with sunspots
- Probably caused when the magnetic field suddenly reorganizes itself
- As charged particles pass into Earth’s Magnetosphere
they create Auroras. (Northern and Southern lights)
Solar Flare
Solar Flare
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Northern Lights – Aurora Borealis (caused by
excessive amount of charged particles hitting
Earth’s Magnetosphere and exciting the gases found
there 25