Energy Energy is a quantity that describes how much force an
object has experienced over a distance or can potentially
experience in a given situation. Energy can be transferred from one
object to another, or transform from one form to another. It can
neither be created nor destroyed. Kinetic Energy: energy that an
object has because of its motion Potential Energy: energy that an
object has because of its position
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The Sun IS NOT an average, yellow star. What is the Sun?
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The Sun is 109 times the diameter of Earth Over 1,000,000
Earths could fit inside the Sun. The Sun is 150 million kilometers
away from Earth. It takes light 8 minutes to travel to Earth from
the Sun. This distance is defined as 1 Astronomical Unit (AU) Earth
Moon Size and Distance of the Sun
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Mass of the Sun
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Rotation of the Sun Galileo saw sunspots that appear to move
across the face of the Sun. Conclusion: the Sun rotates on its
axis. Rotation rate: 27 days (equator) to 31 days (poles) Movie
made from Galileos sunspot drawings from June 2 July 8, 1613
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Luminosity of the Sun
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The Spectrum of the Sun Low Energy Waves High Energy Waves
Visible light is a tiny fraction of the Electromagnetic Spectrum
Gamma rays--billions of waves per inch Radio waves--up to
miles-long wavelengths
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Surface Temperature 5800 K Thermal Spectrum
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Composition of the Sun The spectrum of the Suns light reveals
its composition.
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The Sun produces all the colors of the rainbow in roughly equal
amounts, which is white light. If the Sun were yellow, then white
T-shirts would look yellow in the mid-day sunshine. When you
observe the Sun safely, by projecting its image through a pinhole
camera or a telescope, you see that it is white. Dont stare
directly at the Sun! The UV radiation can damage your eyes. The Sun
is White
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Magnetic Field When an external magnetic field is present,
single energy levels in an atom/ion/molecule split into additional
levels. The amount of splitting and the new energy levels present
depend on the strength and direction (north or south) of the
external magnetic field. Examining the solar spectrum for the
Zeeman Effect allows us to map the magnetic field on the surface of
the Sun.
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Looking at the Sun in different wavelengths of light reveals
different parts of the Sun. Radio light: Wavelength = 17.6 cm See
radiation from Suns atmosphere, Corona The Suns Layers
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Looking at the Sun in different wavelengths of light reveals
different parts of the Sun. Visible light (white light): Wavelength
= 400-700 nm See radiation from Suns surface, Photosphere The Suns
Layers
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Looking at the Sun in different wavelengths of light reveals
different parts of the Sun. Visible light (H-): Wavelength = 656.3
nm See radiation from layer just above Suns surface, Chromosphere
The Suns Layers
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Looking at the Sun in different wavelengths of light reveals
different parts of the Sun. Extreme Ultraviolet light: Wavelength =
30.4 nm See radiation from Suns atmosphere, Corona Image from
STEREO mission The Suns Layers
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Looking at the Sun in different wavelengths of light reveals
different parts of the Sun. Extreme Ultraviolet light: Wavelength =
17.1 nm See radiation from Suns atmosphere, Corona Image from
STEREO mission The Suns Layers
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The Different Parts of the Sun During a total eclipse of the
Sun, the very bright Photosphere is blocked and the Suns outer
atmosphere becomes visible (in white light). We call it the Corona
Spacecraft, like SOHO and STEREO, place a disk in front of their
cameras to create an eclipse. They are then able to take images
with a larger view of the Suns Corona It extends far out into the
Solar System, in fact we live in it!
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Hydrostatic Equilibrium There is no evidence that the Sun has
changed its size, temperature, or luminosity in billions of years.
We therefore conclude that it is in a state of equilibrium. The
forces acting on it are: Gravity from its mass Pressure from its
temperature These forces must be in balance to create
equilibrium.
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Internal Structure Use the Doppler Effect to measure motions on
the surface. Seismic (acoustic) waves can be mapped out by their
appearance on the surface. Just like seismology on Earth.
Helioseismology reveals changes in density and pressure at
different depths inside the Sun.
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The Different Parts of the Sun Core T = 15,700,000 K Density =
162 g/cm 3 Radiative Zone Energy transported by light T =
10,000,000 K Convective Zone Energy transported by convection
Photosphere Visible surface Far less dense than Earths atmosphere T
= 5,800 K Sunspots: T = 4,000 K Chromosphere Thin layer above
photosphere Produces most of Suns UV light T = 10,000 K Corona
Tenuous, extends out millions of kilometers Emits X-rays T =
1,000,000 K
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Energy Source The Suns luminosity has been sustained for
billions of years (geologic and fossil evidence suggest at least
3.8 billion years). What energy source could last that long?
Chemical Burning?: If the Sun were made of coal, burning
(oxidizing: chemical potential energy thermal energy) it could only
sustain the luminosity for ~1,000 years.
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Energy Source The Suns luminosity has been sustained for
billions of years. What energy source could last that long?
Gravitational contraction?: compression of gas from gravity heats
the gas. gravitational potential energy thermal energy (randomized
kinetic energy of the gas particles) original source of energy for
the Sun. could only sustain the Suns luminosity for ~10 million
years. Current energy source for Jupiter and Saturn.
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Nuclear Fusion most common nuclear reaction for Sun-like stars.
4 protons a helium nucleus, positrons, neutrinos, and gamma rays
mass of the 4 protons > the mass of the helium nucleus, the
positrons, and the neutrinos combined. mass gamma ray photons:
proton-proton chain the energy equivalent to the missing mass by
the equation E = mc 2
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Random Walk Photons bounce off of electrons imparting energy to
the plasma (pressure and temperature increase) Plasma is very dense
in core and radiative zone Can take 10,000 -100,000 years for the
energy generated in the core to escape to the surface.
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Extra Slides
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Age of the Sun We think that the Sun and Solar System formed
from a single interstellar cloud all at the same time. So the
oldest rocks in the Solar System should gives us an approximate age
for the Sun as well. Rocks are dated using their relative
abundances of radioactive elements and their decay products. The
oldest rocks on Earth are 4.6 billion years old as are the oldest
meteorites ever examined. So the Sun is at least 4.6 billion years
old. The oldest fossils of life on Earth are 3.8 billion years old.
So the Sun must have reached equilibrium by at least that age. It
burns through fuel at the rate of its luminosity. We figure that
about less than 1% of its mass is available to convert to energy
through fusion. This gives a total lifetime of the Sun at about 10
billion years. Sun
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The Sun is Above Average Most stars in the Universe are small,
cool, low-mass dwarfs. The Sun is larger, hotter, and more massive
than these. There are stars that are much larger, very hot, and
many times more massive than the Sun. But these stars are quite
rare compared to the Sun or the low- mass stars. The Sun is also
not median, mid-range, or most frequent (mode) in the measures of
size, temperature, brightness, or mass.
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Energy Comparisons Food CaloriesJoules Lifting a lemon 1
meter2.388 X 10 -4 1 Car moving at 60 mph863.6 x 10 5 Burning a
liter of oil2871.6 x 10 6 Human daily diet2 X 10 3 8.4 x 10 6
Lightening bolt10 610 Heat a house (1 year)10 7 10 11 1-megaton
H-bomb1 x 10 12 5 x 10 15 Major geomagnetic storm10 12 10 16
Earthquake (magnitude 8.0)6 x 10 12 2.5 x 10 16 Annual U.S. energy
usage10 16 10 20 Impact of dinosaur extinction asteriod 10 19 10 23
Annual sunlight on Earth10 21 10 25 Large solar flare10 22 10 26
Earth spinning10 25 10 29 Earth moving in orbit10 29 10 33 Annual
solar energy output10 30 10 34 Supernova (exploding star)10 40 10
44
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Nuclear Fusion neutrinos ( ) have very little mass, and travel
near the speed of light. They hardly react with anything. They can
escape directly from the core, unlike photons. Hence we can observe
them to probe directly the conditions in the core of the Sun. To do
this we build giant tanks filled with different liquid compounds
and put them far underground. Since neutrinos hardly react to
anything we expect to detect only 1 neutrino per day interacting
with the liquid in the tank! After decades of experiments weve now
actually detected the amount that we expect. But found that we were
detecting all the types of neutrinos, not just those produced by
the proton-proton chain. This means that neutrinos must have some
mass in order to be able to oscillate between the different
types.
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Slide 33
Suns Orbit The Suns orbit is 3D. It takes the Sun about 250
million years to orbit the Galaxy. So the Sun has completed about
18 orbits since its birth (4.5 billion/ 250 million).