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Stars and their Characteristics

Stars and their Characteristics

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Stars and their Characteristics

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  1. Stars and their Characteristics Early Observations Distances to Stars Mass, Size, Temperature Life Cycles of Stars Created by C. Ippolito March 2009

  2. Early Observations • Constellations • groups of stars visualized as “entities” • Big Dipper • best known asterism • part of Ursa Major • Little Dipper • contains polaris (North Star) • part of Ursa minor Created by C. Ippolito March 2009

  3. Apparent Magnitude • measures how bright a star appears to an observer on Earth • First Magnitude (Alpha) • brightest • Sixth Magnitude • faintest • can’t be seen by unaided eye Created by C. Ippolito March 2009

  4. Distances to Stars • Sun • 150 million km = 1 astronomical unit (AU) • Proxima Centauri • 400 trillion km = 260,000 AU • Light year • distance light travels in 1 year • 300,000 km/s = 9.5 trillion km/year • Proxima Centauri • 4.2 light years away • Parallax • change of object’s direction based on observers position • parsec (1 parsec = 3.258 light years = 3.086 x 1013 km Created by C. Ippolito March 2009

  5. Mass, Size, Temperature, Color • Mass • measured in solar masses (# x sun mass) • Color • related to temperature • bluish white (He) • 9,500 °C and above • white (He) • 7,000 °C to 9,500 °C • yellow white (H) • 6,000 °C to 7,000 °C • yellow (H) • 5,200 °C to 6,000 °C • yellow/orange (H) • 3,900 °C to 5,200 °C • red (titanium oxide) • below 3,900 °C Created by C. Ippolito March 2009

  6. Life Cycle of Stars • Hertzsprug-Russell Diagram • plots the luminosity vs. surface temperature • “stages” of life • Main Sequence Stars • 90% of stars • high luminosity/surface temp to low luminosity/surface temp • Supergiants • 100x sun (Betelguese) • Giant Stars • 10x sun (Polaris, Acturus) • White Dwarfs • end of life cycle • former red giants w/o atmosphere Created by C. Ippolito March 2009

  7. Birth of a Star • nebula • 99% hydrogen 1% fine dust (.0001 cm) • protostar • gravity compresses particles • main sequence • longest stage • H fusion to He • red giant or red super giant • H gone, core contracts • shell expands • planetary nebula or supernova • absorb halo of gases or iron core absorbs energy and explodes • white dwarf or black hole or neutron (pulsar) star Created by C. Ippolito March 2009