Chapter 29 Stars Objectives: You will learn… What the structure and processes of the Sun 2. What properties are used to observe and measure stars. 3. How stars change during their “lives” and what is left when they “die”.

I. Properties of the Sun A. Size 1. 10 Jupiter’s side by side 2. 100 Jupiter’s to fill the volume 3. 99 % of the mass of the solar system B. Atmosphere 1. Photosphere (visible surface) a. Inner most layer of atmosphere b. Temperature is 5,800 K c. 400 km thick

2. Chromosphere a. Layer above the photosphere b. Temperature is 30,000 K c. 2,500 km thick 3. Corona a. Outer most layer of the Sun’s atmosphere b. temperature is between 1 and 2 million k c. Several million km thick

??? While the center of the Sun's core can get as hot as 30 million degrees F, its outer layers cool down. And the photosphere, which is outside the core, is cooler still. This is as expected, since normally heat passes outwardly from hot to cold. But the Sun's outermost atmospheric layer is much hotter than its surface layer! Astronomers have puzzled over this enigma for more than 50 years. What is happening on the Sun?

4. Solar Flares a. Violent eruptions of particles of radiation b. Prominence: Arc of gas that is ejected from the photosphere and rains back to the surface

1. Fusion occurs within the Sun’s Core C. Solar Interior 1. Fusion occurs within the Sun’s Core a) When high temp and press combined light hydrogen nuclei into heavier nuclei b) Converts Hydrogen to Helium c) Loss of mass leads to E = mc^2 d) 5 billion years till lights out! 2. Density of 150 g/cm^3 (13 times that of lead) 3. Temperature of 15 million kelvins (27 million degrees Fahrenheit) keeps it in a gaseous state.

D. Three types of Spectra 1. Continuous a) No breaks between the wavelengths b) As seen through a prism, no gas 2. Emission a) See particular wavelength bands b) As seen from a non compressed gas 3. Absorption a) See dark bands along spectrum b) As seen coming through a cool gas see picture in text on page 834

E. Solar Composition 1. 73. 4 % Hydrogen by Mass 2. 25% Helium 3. The rest is trace elements

II Measuring the Stars A. Groups of stars 1. Constellations - name to group with “shape” 2. Star clusters a) Human eye can not distinguish star distances i Stars in same constellation may be very far away from each other 3. Binaries- 2 stars bound to each other w/gravity a) half of the stars we see are binary or multiple star systems

B. Calculating the Distance to Stars 1. Parallax: observed shift in position of stars a) Caused by motion of Earth’s revolution b) A near by star shifts a lot c) A far off star shifts a little

C. Two types of Magnitude for stars 1. Apparent - How bright it appears to be a) Based on distance b) Closer stars may seem brighter c) The lower the number the brighter it is 2. Absolute - How bright it actually is a) Based on size and temperature b) At a distance of 10 pc (32.6 light years)

D. H-R Diagram page 819 in text or in ESRT 1. Absolute magnitude ( at 10 pc) 2. Spectral class ( O, B, A, F, G, K, and M) 3. Temperature ( in Kelvin) 4. Luminosity (star energy per second)

E. Wavelength shift 1. If a star is not moving there is no shift 2. If the star is moving away --> wavelengths extend a) Longer wavelength = red light (red shift) 3. If the star is moving closer --> wavelengths compress a) Shorter wavelength = blue light (blue shift) 4. Evidence in support of the “Big Bang” theory

III Stellar Evolution A Structure of stars 1. Mass and composition determines the: a) temperature i. luminosity ii. rate of nuclear reactions iii. energy output b) balance between gravity and outward pressure i. Hydrostatic equilibrium

B. Stellar evolution and life cycles 1. Birth: Nebula (space gas) 2. Nebula collapses upon self due to gravity 3. As cloud contracts it rotates 4. This rotating disk is called a protostar 5. When temperature rises enough Fusion begins 6. The rest of the cycle depends on the stars mass

C. Life cycle of a medium sized star (ex : the Sun) 1. Converts H to He 2. Loss of mass occurs for 10 billion years 3. Expands to become Red giant a) Surface temperature decreases b) Size increases c) Luminosity increases d) Inner core temp increases e) Helium in core reacts and makes carbon f) Contracts and becomes stable again 4. Returns to normal size a) When helium is used up only carbon is left 5. Becomes nebula again with carbon core (white dwarf)

D. A small star 1. Follows the same sequence as med star but… a) may never form helium core b) proceeds straight to white dwarf c) the white will later become a black dwarf

E. A large star 1. Follows the steps as the other stars until… a) Becomes Red giant many times b) Eventually becomes Super Giant c) If enough mass is lost -> White Dwarf d) if not enough mass is lost -> Neutron star i. 3 times more mass than the Sun ii. Only 10 Km radius!

E. A large star continued e) Some neutron stars are unique in that they have a pulsating pattern of light.

f) Supernova: explosion of neutron star f) Supernova: explosion of neutron star. A distant supernova might be more bright than the galaxy that its in.

F. Largest stars 1. Too big to turn into neutron stars 2. Collapses forever to form Black holes a) So dense that not even light can escape