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 Supernov a White Dwarf Neutro n Star Black Hole Protost ar Massive Star ( Huge) Red Supergiant Massive Star (Giant) Red Supergiant Superno va 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 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 L 2L 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 HR Diagram Interacative Lab Stellar Evolution/H-R Diagram Simulation Astronomy Place Tutorials 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