Review Sheet: Test 2
Date of Exam: August 17, 2009

Version Date: August 14, 2009
Material: Class notes (Topics 3 (radii and later), 4, & 5) and Web notes. Please check and use your class notes to determine how far to cover in the webnotes.
Formulas:

Blackbody Laws:

Wien's Law -- The wavelength at which a blackbody appears the brightest is inversely proportional to the temperature of the blackbody, i.e.,
W = 3x10⁷/T(K) Angstroms, or T = 3x10⁷/W K, where 1 Angstrom = 10^-8cm

Stefan-Boltzmann Law -- The power radiated per unit area from a blackbody is proportional to fourth power of the temperature, i.e.,
Flux = constant x T⁴

Old Test 1 from an earlier time I taught ASTR 122.
Topics:
Stellar Properties:

What are the ranges for the properties of stars? (What is the most important property of stars mentioned in class?)
How do we determine radii, temperatures, and luminositites of stars? What is the hardest part of determining the luminosities of stars?
How could we determine the distance to Sun? What method for the determination of stellar radii has (historically) been the most useful? Roughly, how does the method work?
What is the difference between flux and luminosity? Of flux (energy flow per unit area and per unit time) and luminosity (total power). Which determines how bright an object appears to us (an observer on Earth?) The total emission from an object over all wavelengths is its bolometric luminosity. How are bolometric luminosities determined?
What are the three kinds of spectra usually encountered in astrophysics?
How are stellar spectra formed? What are Kirchhoff's laws of spectral formation?
What information can be extracted from spectra (both from continuous and absorption line spectra)? How is information extracted from spectra?
Discuss how atoms are put together (what are electons, protons, and neutrons?), How large is an atom? How large is the nucleus of an atom? Where is most of the mass of an atom contained? What force holds an atom together? What force holds the nucleus together? What determines the type of element an atom is? What is an isotope?
Why does the line spectrum serve as the fingerprint of an element? How do absorption and emission lines arise? What are Lyman lines, Balmer lines, Paschen lines, Brackett lines, and Pfund lines?
Roughly sketch the energy level diagram for a hydrogen atom. On your diagram draw arrows to indicate an absorption process, an emission process, an ionization process, and a recombination process. Draw another energy level diagram for hydrogen and then indicate the Lyman, Balmer, Paschen, Brackett, and Pfund transitions.
Spectral Classification. What is the Morgan-Keenan (MK) spectral classification scheme? How are spectra classified in the MK scheme? (What criteria are used to classify stellar spectra?) Why do different stars have different appearing spectra? Explain why the strength of the hydrogren lines change as you go from O --> M.
What is meant by HI, HII, CaII, Fe XXVI? More to the point what is meant the Roman Numerals appended to the abbreviations for the elements?
How can we infer that the Sun (or any star) contains iron or other elements such as carbon, oxygen, nitrogen, and so on.
What important stellar property is carried by the spectral class of a star? List the order of the spectral classes from high to low temperature.
What are the Luminosity Classses? For what types of star do the symbols I, III, and V stand?
What is a blackbody? Give an example of a blackbody? What is the most perfect blackbody known? What characeristic of a blackbody determines its properties? What are the Wien Law and Stefan-Boltzmann Law? Which blackbody law is used (and how may it be used to determine stellar temperatures)? Why are blackbodies interesting and useful idealizations for astronomers? How does the color of a blackbody depend on its temperature? (Draw a plot to support your answer.) Which of the following blackbodies produces the most IR radiation, a 10,000 K blackbody or a 3,000 K blackobdy. Which of the two previous blackbodies appears the reddest?

Hertzsprung-Russell Diagram

What is the utility of making plots of large data sets? What do correlations in plots mean? What don't correlations in plots show?
What is the Herzsprung-Russell Diagram (H-R)? Draw an H-R diagram and carefully label the axes and the various portions of the diagram. Carefully mark the location of the Sun.
What information can we deduce about how stars evolve using how stars cluster in the HR diagram? Where do we find the largest (in diameter) stars in the HR diagram? Where do we find the smallest (in diameter) stars in the HD diagram?
What is the Russell-Vogt theorem? State the Russell-Vogt theorem. What is the most important stellar parameter?