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Characteristics of Stars. Temperature/Color Mass Luminosity Absolute Magnitude Apparent Magnitude. The mass of a star determines the length of its life cycle (how long will it burn). Life Cycle of a Star. White Dwarf. Planetary Nebula. Red Giant. Shrinks
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Characteristics of Stars • Temperature/Color • Mass • Luminosity • Absolute Magnitude • Apparent Magnitude
The mass of a star determines the length of its life cycle (how long will it burn).
Life Cycle of a Star White Dwarf Planetary Nebula Red Giant • Shrinks • Few thousand miles in diameter • No nuclear reactions Sun (main sequence star) • Nuclear decreases • Core contracts • Outer layers expand • Outer layers drift to outer space • Outer layers lost to nebula • Longest period of a star’s life Massive Star (Giant) Massive Star ( Huge) Red Supergiant Red Supergiant Protostar Stellar Nebula (nursery) • Core collapses instantly • Massive short-lived explosion • Outer layers blown away • Shrinks to small dense star • Very strong gravity Neutron Star • Nuclear decreases • Core contracts • Outer layers expand • Longest period of a star’s life Black Hole Supernova Supernova • Very strong gravity that light can’t escape
Two Kinds of Brightness • Apparent Magnitude:How bright the object appears to us on Earth. • Absolute Magnitude:How bright a star actually is.
Which star appears brighter to the observer? Star B 2L L Star A d 2d
Which star looks like it is giving off more light? • But, which star is actually giving off more light?
Life Cycle of Stars Interactive Investigation http://aspire.cosmic-ray.org/labs/star_life/starlife_main.html • HR Diagram Interacative Lab http://aspire.cosmic-ray.org/labs/star_life/hr_interactive.html • Stellar Evolution/H-R Diagram Simulation http://instruct1.cit.cornell.edu/courses/astro101/java/evolve/evolve.htm • Astronomy Place Tutorials http://media.pearsoncmg.com/bc/bc_bennett_cosmicpers_2/medialib/tutorials/index.html
Properties of Stars • Mass – The single most important property that determines other properties of the star. • Luminosity – The total amount of energy (light) that a star emits into space. • Temperature – surface temperature, closely related to the luminosity and colorof the star. • Spectral type – closely related to the surface temperature • Size – together with temperature determine the luminosity
What can we measure directly? The Easy Ones: • Apparent brightness: a well-calibrated detector. • Temperature: spectroscopy • Spectral type: spectroscopy