Stars and their Characteristics
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Transcript of Stars and their Characteristics
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Updated Created by C. IppolitoMarch 2009
Stars and their Characteristics
Early ObservationsDistances to StarsMass, Size, TemperatureLife Cycles of Stars
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Updated Created by C. IppolitoMarch 2009
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
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Updated Created by C. IppolitoMarch 2009
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
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Updated Created by C. IppolitoMarch 2009
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
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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
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Updated Created by C. IppolitoMarch 2009
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
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Updated Created by C. IppolitoMarch 2009
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