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