1. Note key, please leave in binder. Our Sun
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Understanding Stars
Our Sun
Shooting stars movie opener.

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Our Sun
What is the structure of our sun?
What makes the sun shine?
How do we know?
What tools do we use to study our nearest star?

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What tools do we use?
Refracting telescopes- light passes through a lens to the eye
Good clarity, good power, good magnification,
High quality lenses needed, chromatic aberration
Reflecting telescopes- uses a mirror to focus light
Good clarity, good power, good magnification, glass not as high quality
Secondary mirror blocks some light
Radio Telescopes-focus incoming radio waves on an antenna, can be arranged in arrays
X-Ray telescopes- detect incoming X-rays, space telescopes, focus on learning about black holes
Gamma Ray telescopes - space telescopes to study visible light and gamma rays.
And others. . .

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How do we know?
Spectroscopy - the study of the properties of light
Detailed study of this in physics
Depends on the wavelength
Think a rainbow = continuous spectrum

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How do we know?
Absorption spectrum - when light is passed through cool gas under low pressure the gas will absorb some light and leave dark bands on the spectrum.

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How do we know?
Emission Spectrum - when light is passed through HOT gas under low pressure the gas will emit some light and these appear as bright bands on a dark spectrum. These act as finger prints to stars and tell us the chemical composition of stars.

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Structure of the Sun
Photosphere = visible surface
Interior
Atmospheric layers (2)
Chromosphere
Corona

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Photosphere
Visible surface of the sun
Appears to have a grainy texture.
Called granules
size of TX
last min
Due to convection within the sun
Composed of 90% hydrogen, and <10% helium.

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Sunspots
Dark areas on surface (photosphere)
Dark due to lower temperature
Show sun activity and rotation of sun
More spots = higher solar activity, 11 year cycle

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Chromosphere
Layer of atmosphere, thin (few thousand km)
Visible during an eclipse
Magnetic field evidence of the sun present in this layer.
Dark webbed lines = magnetic fields
Image courtesy University of Michigan

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Prominences
Arches or loops of chromospheric gases
Extend into corona
Ionized gases that are trapped by magnetic fields.
Show areas of intense activity

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Corona
Outermost portion of solar atmosphere
Origin of solar wind, aka space weather
Energy travels at speeds up to 800km/sec.
Solar flares
Image by SOHO

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Solar Flares
Explosive solar events
Release enormous amounts of energy in form of UV, radio, and X-rays
Cause an increase in intensity of solar wind due to atomic particles that are ejected

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NASA SDO example
SDO = Solar Dynamics Observatory; Recorded in extreme UV range (gives purple/green color); X-class flares are big; they are major events that can trigger planet-wide radio blackouts and long-lasting radiation storms. M-class flares are medium-sized; they can cause brief radio blackouts that affect Earth's polar regions. Minor radiation storms sometimes follow an M-class flare. Compared to X- and M-class events, C-class flares are small with few noticeable consequences here on Earth.
SDO = Solar Dynamics Observatory
M5.6 class solar flare (Almost X class)
7/2/2012

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Why does the sun shine?
Nuclear fusion (opposite of fission) in the interior or core.
Stars use nuclear fusion to combine light/low mass elements into heavier/higher mass elements.
Matter is converted to energy
4 hydrogen combine to form one helium.
One proton in each hydrogen atom, atomic mass = atomic mass units
One helium atom, atomic mass = atomic mass units

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Why does the sun shine?
Stars use nuclear fusion to combine light/low mass elements into heavier/higher mass elements.
Results in a small loss of mass as the mass is converted into energy
Difference in atomic masses = atomic mass units.
Energy! E = mc2