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Class 1 Introduction, Background History of Modern Astronomy The Night Sky, Eclipses and the Seasons Kepler's Laws Newtonian Gravity General Relativity Matter and Light Telescopes Class 2 Solar System Characteristics Formation Exosolar Planets

Class 3

Stars The S un Stellar Evolution of Low and High Mass Stars Deaths of Stars Exotic Stars

Class 4 Galaxies Galaxy Classification Formation of Galaxies Galactic Evolution Class 5 Cosmology Large-Scale Structure of the Universe Big Bang Cosmology Class 6 Special Topics Requested Topics for Discussion Observing with a Telescope


The Sun
http://www.boston.com/bigpicture/2008/10/the_sun.html


Structure of the sun


Core Radiation zone interior Convection zone Photosphere (surface) Chromosphere atmosphere Transition zone Corona

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A star is in equilibrium when the inward and outward forces are in balance, which our Sun will be for about another five billion years.


Observables

Every second, the sun produces energy equivalent to detonation of about 100 billion 1-megaton nuclear bombs. another way, the solar luminosity (L) is equivalent to 4 tr trillion l00-watt light bulbs shining simultaneously--about dollars' worth of energy radiated per second (at 1995 rates). L = 4 x 1026 Watts

the Put illion 1019


The blackbody spe s spectrum (photospheric light) corresponds to a temperature of 5777K.

Obsemvaebles n' ratch s the su ctrum that


Observables
The absorption lines in the solar spectrum are caused by the cooler layer above the photosphere, the chromosphere, which absorbs specific colors according to what elements are present.

The absorption lines tell us the composition of t he S un.


Neutrino detectors count the only observable that comes directly from the core. Neutrinos are produced in hydrogen fusion, which proceeds most commonly by the proton-proton chain in the core.

Observables


The differential rotat

Obsecreates tblest rva ension in ion of the sun

he sun's magnetic field.

The diverse phenomena that result are observable as sunspots, prominences, solar flares, ..


Stellar Evolution


Recall:

A star is in equilibrium when the inward and outward forces are in balance, which our Sun will be for about another five billion years.

But, the balance of forces can change. A temperature increase will lead to expansion.

The presence and rate of nuclear fusion, "burning", affects the temperature of the core.


The initial mass of a star determines a star's life cycle.
Low mass stars live and die differently than high mass stars. A high mass star (15 or 20 times the mass of the sun) dies as a neutron star or black hole.

A one solar mass star dies as a white dwarf.


Two fundamental properties of a star can change when the balance of forces shifts and a star ages into the next stage of life. L, luminosity T, surface temperature as measured by the apparent brightness and distance to the star to calculate its luminosity, and as measured by colors of the stars (taking its spectrum or observing the star with different color filters) to calculate its surface temperature.


When either of those properties change, the star's position on the Hertzsprung-Russell diagram will change. This luminosity-color plot, the HR diagram, is instrumental to understanding stellar evolution.


Where a star is located on the HR diagram tells you about its state of evolution. Stars of masses different diagram different different take paths in the over time scales.

High mass stars might live as short as 10 million years whereas the lowest mass stars will live up to 10 trillion years.



HR diagrams of globular clusters help interpret stellar evolution. Highest mass stars evolve off the main sequence if hydrogen fusion has completed. This provides an age estimate of the object since we know how fast stars of different masses will live in each stage of life.


Deaths of Stars


"Pre-death"
Before a low mass star becomes a planetary nebula and ultimately a white dwarf it has two layers of shell burning and a carbon core.

A high mass star will burn heavier and heavier elements at its core, along with layers of shell burning, until iron ash accumulates and core burning ends, before it undergoes a supernova.


A high mass star (15 or 20 times the mass of the sun) dies as a neutron star or black hole, such a the Crab Nebula which contains a neutron star at the center.

A one solar mass star dies as a white dwarf, such as Sirius B.