stars and their characteristics
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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) - PowerPoint PPT PresentationTRANSCRIPT
Updated Created by C. IppolitoMarch 2009
Stars and their Characteristics
Early ObservationsDistances to StarsMass, Size, TemperatureLife Cycles of Stars
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
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
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
Updated Created by C. IppolitoMarch 2009
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
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
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