NJIT Physics 320: Astronomy and Astrophysics – Lecture VIII Carsten Denker Physics Department Center for Solar–Terrestrial Research

October 22nd, 2003NJIT Center for Solar-Terrestrial Research Problem 6.5

October 22nd, 2003NJIT Center for Solar-Terrestrial Research Problem 6.6

October 22nd, 2003NJIT Center for Solar-Terrestrial Research Problem 6.8

October 22nd, 2003NJIT Center for Solar-Terrestrial Research Problem 6.9

October 22nd, 2003NJIT Center for Solar-Terrestrial Research Stellar Atmospheres  The Description of the Radiation Field  Stellar Opacity  Radiative Transfer  The Structure of Spectral Lines

October 22nd, 2003NJIT Center for Solar-Terrestrial Research Radiation Field

October 22nd, 2003NJIT Center for Solar-Terrestrial Research Energy Density

October 22nd, 2003NJIT Center for Solar-Terrestrial Research Energy Density (cont.)

October 22nd, 2003NJIT Center for Solar-Terrestrial Research Radiation Pressure

October 22nd, 2003NJIT Center for Solar-Terrestrial Research Solar Spectrum The spectrum of the Sun: The dashed line is the curve of an ideal blackbody having the Sun’s effective temperature.

October 22nd, 2003NJIT Center for Solar-Terrestrial Research Temperature Definitions

October 22nd, 2003NJIT Center for Solar-Terrestrial Research Blackbody A blackbody radiator has a number of special characteristics. (1) A blackbody emits some energy at all wavelength. (2) A hotter blackbody emits more energy per unit area and time at all wavelength than does the cooler one. (3) A blackbody emits a greater portion of radiation at shorter wavelength than does a cooler on. (4) The amount of radiation per second per unit surface area of a blackbody depends on the fourth power of the temperature.

October 22nd, 2003NJIT Center for Solar-Terrestrial Research Thermodynamic Equilibrium Excitation, ionization, kinetic, and color temperature are the same for the simple case of a gas confined in a box. The confined gas particles and blackbody radiation will come into equilibrium, individually and with each other, and can be described by a single well–defined temperature. In such a steady–state condition, no net flow of energy through the box or between the matter and radiation occurs. Every process (e.g., the absorption of a photon) occurs at the same rate as its inverse process (e.g., the emission of a photon). This condition is called thermodynamic equilibrium. The idealized case of a single temperature can still be employed if the distance over which the temperature changes significantly is large compared with the distance traveled by the particles and photons between collisions (their mean free path). In this case, referred to as local thermodynamic equilibrium (LTE), the particles and photons cannot escape the local environment of nearly constant temperature.

October 22nd, 2003NJIT Center for Solar-Terrestrial Research Homework Class Project  Continue improving the PPT presentation.  Use the abstract from the previous assignment as a starting point for a PowerPoint presentation.  The PPT presentation should have between 5 and 10 slides.  Bring a print-out of the draft version to the next class as a discussion template for group work  Homework is due Wednesday October 29 th, 2003 at the beginning of the lecture!  Exhibition name competition!

October 22nd, 2003NJIT Center for Solar-Terrestrial Research Homework  Homework is due Wednesday October 22 nd, 2003 at the beginning of the lecture!  Homework assignment: Problems 9.1, 9.2, and 9.7!  Late homework receives only half the credit!  The homework is group homework!  Homework should be handed in as a text document!