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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). Sun (main sequence star) •Longest period of a star’s life Stellar Nebul a (nursery ) Protost ar White Dwarf Red •Nuclear Giant decreases •Core contracts •Outer layers expand Massive Star ( Huge) •Longest period of a star’s life Red Supergiant Planetary •Outer layers drift Nebula to outer space •Outer layers lost to nebula •Nuclear decreases •Core contracts •Outer layers expand Superno •Core vacollapses instantly •Massive shortlived explosion •Outer layers blown away •Shrinks •Few thousand miles in diameter •No nuclear reactions Neutro n Star •Shrinks to small dense star •Very strong gravity Black Massive Star (Giant) Red Supernov •Very strong gravit Hole 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? O B A F G K M • 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/inde x.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 color of 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