How luminous are stars?
Luminosity is the the amount of power a star has.
Apparent brightness is amount of starlight that reaches earth.
Luminosity passing through each sphere is the same.
Divide luminosity by area to get brightness.
Parallax is the apparent shift in position of nearby objects against background of more distant objects, depends on distance.
Apparent position of nearest shift about an arcsecond as earth orbits the sun.
Parallax is measured by comparing snapshots taken at different times and measuring the shifts in angle to star.
How hot are the stars?
Every object emits thermal radiation with spectrum.
An object fixed sizes grows more luminous as it rises in tempature.
Hotter objects omit more light wave lengths.
Hotter objects tend to emit light at a shorter wavelengths and higher frequencies.
Lines in a star's spectrum correspond to a spectral type that reveals its tempature.
How Massive are stars?
The orbit is determined by the strenght of gravity.
Binary Stars are visual, eclipse, spectroscopic
We can directly observe the orbital motions of the stars.
We can measure periodic eclipses
We determine the orbit by measuring Doppler shifts
How do we classify stars?
Brightest stars are reddish
Color and luminosity are closely related among remaining "normal" stars
Main sequence stars are fusing hydrogen into helium in their cores like the sun.
Blue stars are main sequence
less luminous are yellow.
Why is a star's mass more important property?
each star's properties depend mostly on mass and age.
Luminosity from brightness and distance.
temperature from color and spectral type
mass from period and average separation of binary star orbit.
Core pressure and temperature of a higher mass star need to be larger in order to balance gravity.
higher core temp. boost fusion rate leading to larger luminosity.
High mass:
High Luminosity
short lived
Large Raduis
Blue
Low mass
Low luminosity
Long lived
Small raduis
Red
What is a Hertzsprung-Russell Diagram?
Normal Hydrogen is located on main sequence of H-R diagram.
H-R Depicts:
Temp
Color
Spectral Type
Lumiosity
Radius
mass
Age
Life span
What are the two types of star clusters
Open cluster: loose stars
Globular Cluster" densely packed stars
how do we measure the age of star cluster?
Massive blue stars die first.
To determine accurate ages we compare models of stellar evolution.
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