Red Giants and White Dwarfs. A Field Guide to Stars. The Solar Neighborhood. Milky Way Galaxy 100 billion stars Volume of nearly 100,000 light years across Orbits Galactic Center- 25,000 light years from Earth. Stellar Parallax. Measuring Parsecs. Parallax decreases as distance increases
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A Field Guide to Stars
Milky Way Galaxy
100 billion stars
Volume of nearly 100,000 light years across
Orbits Galactic Center- 25,000 light years from Earth
parallax (in arc seconds)
One Parsec≈3.3 Light years
Alpha Centauri Complex
4.3 Light years
Luminosity is intrinsic also called the absolute brightness
We see apparent brightness
Leaving a star, light travels through imaginary spheres of increasing radius surrounding the source.
Apparent brightness (energy flux)∞ luminosity
Ranges from the Sun (-26.7) to the Hubble/Keck limit
Calculate the luminosity (in solar units) of a star having absolute magnitude of M. The star’s absolute magnitude differs from the Sun by (M-4.83) magnitudes, So the luminosity, L, differs from the solar luminosity by a factor of:
100 -(M-4.83)/5 or
L(solar units)= 10–((M-4.83)/2.5)
From appendix 3:
MSun=4.83, has L=100=1
Sirius A with M=1.45, has L=101.35=22 Solar Units
B and V filters admit different amounts of light for objects of different temperatures.
Relationship exists between stellar temperature and luminosity