stars
TRANSCRIPT
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Stars
How They Are Classified
and
How They Work
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Birth of a Star
• Nebula - a cloud of gas and dust in space.
• Some nebulas are where stars are formed or are the remains of dead or dying stars
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Hertzsprung-Russell Diagram
• Graph showing the luminosity (objects radiation) of a star as a function of its surface temperature.
• Luminosity is measured in terms of absolute magnitude.
• Absolute magnitude is the brightness of a star.• Brightest stars are of 1st magnitude and the
dimmest stars are of 6th magnitude.
• The sun has a magnitude of -26.8 (really, really, really bright)
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X-Axis
Y-Axis
Most Stars areon the Main Sequence. TheSun is on here.
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Absolute versus Apparent Magnitude
Absolute Magnitude:• The brightness that a
star would have at distance of 32.6 light-years from Earth.
Apparent Magnitude:• The brightness of a
star as seen from the Earth.
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What Fuels Stars?
• Nuclear Fusion - Hydrogen and Helium coming together to produce energy and light
• The most well known star that affects our lives every day is the SUN.
• It take approximately 8 minutes and 18 seconds for light to reach earth from the sun.
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The Core• Gravity pulls all of the mass inward and
creates an intense pressure.
• The pressure is high enough to force atoms of hydrogen to come together in nuclear fusion reactions.
• Two atoms of hydrogen are combined to create helium-4 and energy (light)
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Radiative Zone
• In this zone, the energy from the core is carried outward by photons.
• As one photon is made, it travels about 1 micron (1 millionth of a meter) before being absorbed by a gas molecule.
• The gas molecule is heated and re-emits another photon of the same wavelength.
• The cycle repeats itself until a photon reaches the convective zone.
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Convective Zone
• Dominated by convection currents that carry the energy outward to the surface (convection currents are rising movements of hot gas next to falling movements of cool gas).
• Carry photons outward to the surface faster than the radiative transfer that occurs in the core and radiative zone.
• It takes a photon approximately 100,000 to 200,000 years to reach the surface!
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The Sun’s Atmosphere
• Photosphere
• Chromosphere
• Corona - extremely hot outermost layer extending outward from the chromosphere several million miles or kilometers
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Photosphere• Is the region that can be seen from Earth
• Has an average temperature of 5,800 degrees Kelvin
• As we pass up through the photosphere, the temperature drops and does not emit as much light energy.
• Therefore, the outer edge of the photosphere looks dark, an effect called limb darkening that accounts for the clear crisp edge of the sun's surface.
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Chromosphere
• Lies above the photosphere.
• The temperature rises across the chromosphere.
• Thought to be heated by convection within the underlying photosphere.
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Corona• Final layer of the sun and extends several
million miles or kilometers outward from the photosphere.
• Can be seen best during a solar eclipse and in X-ray images of the sun.
• The corona has bright areas (hot) and dark areas called coronal holes.
• Coronal holes are relatively cool and are thought to be areas where particles of the solar wind escape.
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Suns Corona
Total Solar Eclipse 2/26/1998 from Maricaibo, Venezuela
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Features on the Sun
• Sunspots
• Solar Prominences
• Solar Flare
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Sunspots
• Dark, cool areas that appear on the photosphere.
• Always appear in pairs.
• Are intense magnetic fields (about 5,000 times greater than the Earth's magnetic field) that break through the surface.
• The magnetic field is caused by movements of gases in the sun's interior
• Sunspots happen in 11-year cycles (it is not known why they occur in 11-year cycles).
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Solar Prominences
• Clouds of gas that rise from the chromosphere.
• Appear as arches.• Can last two to three
months and extend as far out as 30,000 miles from sun’s surface.
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Solar Prominences
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Solar Flares
• Violent explosions from the sun.
• Thought to be caused by sudden changes in the magnetic field where the magnetic field is concentrated.
• Accompanied by the release of gas, electrons, visible light, ultraviolet light and X-rays.
• Produce auroras and can disrupt communications systems on Earth when the release of energy caused by these violent eruptions reaches Earth.
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Solar Flares
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Fate of the Sun• The sun has been shining for about 4.5 billion
years.
• It has enough hydrogen fuel to "burn" for about 10 billion years.
• The size of the sun is a balance between the outward pressure made by the release of energy from nuclear fusion and the inward pull of gravity.
• When the core runs out of hydrogen fuel, it will contract under the weight of gravity and expand becoming a Red Giant.
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Fate of the Sun Continued• When the sun becomes a Red Giant it’s
expansion will reach beyond Earth’s orbit and therefore, the earth will be vaporized!!!!!
• At some point the helium will fuse into carbon and when there is no more helium the core will expand and cool and become a White Dwarf
• After becoming a White Dwarf the sun will then turn into a Black Dwarf.
• The entire process will take a few billion years.
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