11/7 Notes

Louis Lackey

Day 12 Notes

Chapter 11- Surveying the stars

Section 11.1- Properties of Stars

            We measure luminosities by the amount of light passing through each unit of area depends on the inverse square of its distance from the star. Brightness of a star depends on distance and luminosity. Luminosity is the amount of power a star radiates. Energy per second is Watts. Apparent brightness is the amount of starlight that reaches earth, energy per second per square meter. You divide luminosity by area to get brightness. Brightness=Luminosity/4pi(distance)^2

            Apparent positions of stars shift by about an arc second as earth orbits the sun. We use parallax and trigonometry to measure the distance of stars. We measure stellar temperatures using the color spectrum. We can only measure mass in binary systems by measuring eclipses, because of orbits and gravity.

Section 11.2 Patterns among stars

            A Hertzsprung russel diagram organizes stars based on temperature and luminosity. Most stars lie on the main sequence. Stars with lower T and higher L than main sequence stars must have larger radii-Giants and Supergiants. Lower T/L must be smaller-White Dwarfs. There are five classes of stars-

I-supergiant

II-Bright giant

III-giant

IV-Subgiant

V-Main Sequence

            A stars full classification includes spectral type (OBAFGKM), temperature, color, luminosity, and radius

            Main sequence stars are fusing H into He.

Luminosity-brightness distance

Temperature-color and spectral type

Mass-period and separation of binary orbit

            Mass and lifetime- the sun is halfway through its 10 billion year life. Larger stars burn faster and have shorter lives, smaller longer.

            Stars that have finished fusing H are off the main sequence. They become larger and redder. After fusion has ceased they become white dwarfs.