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).
Stellar Nebul
a(nursery
)
Sun (main sequence
star)
Red Giant
Planetary Nebula
Supernova
White Dwarf
Neutron Star
Black Hole
Protostar
Massive Star ( Huge) Red
Supergiant
Massive Star (Giant)
Red Supergiant
Supernova
•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
•Longest period of a star’s life
•Nuclear decreases•Core contracts•Outer layers expand
•Core collapses instantly•Massive short-lived explosion•Outer layers blown away
•Shrinks •Few thousand miles in diameter•No nuclear reactions
•Shrinks to small dense star •Very strong gravity
•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?
d
2d
L2L
Star B
Star A
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 Simulationhttp://instruct1.cit.cornell.edu/courses/astro101/java/evolve/evolve.htm
• Astronomy Place Tutorialshttp://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 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