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Stars and their Characteristics

Stars and their Characteristics. Early Observations Distances to Stars Mass, Size, Temperature Life Cycles of Stars. Early Observations. Constellations groups of stars visualized as “entities” Big Dipper best known asterism part of Ursa Major Little Dipper contains polaris (North Star)

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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

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