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    Stars Stars Presentation Transcript

    • Stars How They Are Classified and How They Work
    • 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
    • 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)
    • Most Stars are on the Main Sequence. The Sun is on here. Y-Axis X-Axis
    • Absolute versus Apparent Magnitude Absolute Magnitude: • The brightness that a star would have at distance of 32.6 lightyears from Earth. Apparent Magnitude: • The brightness of a star as seen from the Earth.
    • 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.
    • Parts of the Sun (click picture)
    • 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)
    • 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.
    • 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!
    • The Sun’s Atmosphere • Photosphere • Chromosphere • Corona - extremely hot outermost layer extending outward from the chromosphere several million miles or kilometers
    • 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.
    • Chromosphere • Lies above the photosphere. • The temperature rises across the chromosphere. • Thought to be heated by convection within the underlying photosphere.
    • 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.
    • Suns Corona Total Solar Eclipse 2/26/1998 from Maricaibo, Venezuela
    • Features on the Sun • Sunspots • Solar Prominences • Solar Flare
    • 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).
    • 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.
    • Solar Prominences
    • 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.
    • Solar Flares
    • Solar Flare Click on Picture Earth
    • 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.
    • 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.