Life of the Sun When the Sun started shining as a star on the main sequence, what was its luminosity compared to today? What happens on the Earth in 1.1 billion years when the Sun reaches 1.1 LSun now? 3. What might prevent that disaster from happening? Why might the Earth not get engulfed by the expanding Sun? Name any future phase of the Sun other than red giant. B. How long does the Sun last on the main sequence?

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Life of the Sun When the Sun started shining as a star on the main sequence, what was its luminosity compared to today? 0.7 LSun now What happens on the Earth in 1.1 billion years when the Sun reaches 1.1 LSun now? moist greenhouse effect 3. What might prevent that disaster from happening? clouds Why might the Earth not get engulfed by the expanding Sun? mass loss Name any future phase of the Sun other than red giant. subgiant, [red giant], horizontal branch, asymptotic giant branch, pulsating AGB, planetary nebula, white dwarf, [black dwarf] B. How long does the Sun last on the main sequence? 11 Gyr

Russell Diagram first HR Diagram from Russell (1914) spectral types used white dwarf is 40 Eri B

Super HR Diagram

Star Colors

RECONS HR Diagram

Sun Among Stars Average medium type there are hotter/cooler stars, bigger/smaller stars Sun is “average” typical or common type 89% of stars are smaller, cooler than the Sun Sun is NOT “average”

Hipparcos + HR Diagram Hipparcos: faint dots future SIM: blue future Gaia: yellow Supergiants: best guesses O Stars: best guesses PNe central stars: Harris white dwarfs: Subasavage blue regions are for SIM; yellow regions are for Gaia

HR Diagram: Famous Stars range 108 L ~ R2 T4 keep T constant 108 ~ R2 104 ~ R

Star “Genetics” MASS IS (nearly) ALL ! Star Genetics mass central temperature fuel reactions … structure  energy released … luminosity … absolute mag radius  surface temp … color … spectral type evolution lifetime end state MASS IS (nearly) ALL ! multiplicity … interactions composition … slight tweaks

Sun’s Composition 99.9%

The Stellar Struggle A STAR is a gas ball … gravity pulling in, radiation pressure pushing out

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