Review Sheet: Test I
Date of Exam: 2 August 2007

Reading: Class notes, Web notes, parts of Chapters 3, 4, & 16, Chapter 17

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

• Flux from a star at distance, D:
  Flux ~ Power / (3.1 D²)

• Luminosity of a star of temperature T and radius R:
  L = 12.6 constant R² T⁴

Topics:

Introduction

• Why do we study stars? What makes the understanding of stars interesting, beyond the intrinsic value of having knowledge for knowledge's sake?
• In what ways do stars serve as physics laboratories? What are neutrinos? How does the Sun generate energy? What are the Super-K and SNO experiments? Five years ago, we thought that there was a lack of Solar neutrinos from the Sun, how has our viewpoint changed since then? What have we learned about neutrinos as a result of the Solar Neutrino Experiment? Why are neutrinos a more interesting probe of the Sun than are the photons (electromagnetic radiation) we receive from the Sun?
• What is nucleosynthesis? What does it have to do with stars and the Earth? What was the initial chemical composition of the Universe?
• What are neutron stars? What are strange stars?
• Does the Sun affect the climate on the Earth? Is there evidence which suggests that the Sun affects (or does not affect) the climate on the Earth? What are sunspots? What are prominences? What are filaments? What is the period of the solar activity cycle? The period for the variation of the number of sunspots visible on the surface of the Sun? What is the Maunder minimum? What is the significance of the Maunder minimum and the Little Ice Age which struck Europe in the mid 1600s (in terms of Solar variability)? Roughly, how large is the variation of the Solar power (Solar constant) output (luminosity) over a Sunspot cycle? Are there noticeable effects of this variation on the climate of the Earth?
• How do we study stars? What are the most important ways which we use to study stars (e.g., light, particles, ...)? Historically, what has been the most useful method to study stars? Why? What makes the study of stars from an observational standpoint difficult? For example, which parts of the electromagnetic energy are blocked by the Earth's atmosphere? Which parts of the electromagnetic spectrum penetrate to the surface of the Earth? How do we perform experiments on stars (can we perform experiments on stars in the normal sense)?
• What is electromagnetic radiation (E & M)? Physically, what is E & M radiation? What is meant by electromagnetic spectrum? What are the parts of the electromagnetic spectrum in order of increasing wavelength (in order of increasing frequency)? Define wavelength and frequency. How are wavelength and frequency related to the energy of light? Which has the longer wavelength, blue or red light?

Stellar Properties:

• What are the ranges for the properties of stars? (what is the most important property of stars we mentioned in class?)
• How do we determine the diameters (radii), masses, spectral classes, luminositites of stars? What is the hardest part of determining the luminosities of stars?
• What is the difference between flux and luminosity? Of flux and luminosity, which determines how bright an object appears to us (an observer on Earth?)
• 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 (from both continuous and absorption line spectra)? How is information extracted from continuous and line spectra? Consider how atoms are put together (what are electons, protons, and neutrons), What is the rough size of an atom? What is the size of the nucleus of an atom? What force holds an atom together? What foce holds the nucleus of an atom together? The line spectrum of an element serves as the fingerprint of an element. Why do elements have unique line spectra? What aspect of quantum mechanics contributes to our understanding of why elements have unique line spectra (hint: energy comes in packets called quanta)? Briefly, describe the structure of an atom. What property of an atom determines which type of element the atom is?
• What is the spectral classification scheme (as based on the strengths of the absorption lines in the spectra)? How are different spectra classified? (What criteria are used to classify stellar spectra?) Why do different stars have different appearing spectra? Do they have grossly different chemical compositions? Explain why the strength of the hydrogren lines change as you go from O --> A --> M.
• What important stellar property is carried by the spectral class of a star?
• What are the Luminosity Classses? For what do I, III, and V stand?
• What is a blackbody? Why are blackbodies interesting and useful? How can the properties of a black body be used to infer properties of stars from their spectra?
• Sketch the energy level diagram for hydrogen. Sketch and label the Lyman transtions, Balmer transitions, Paschen transitions, Brackett transtions, Pfund transitions. Indicate both emisssion and absorption lines. What is ionization? What is recombination? Which hydrogen series falls in the optical portion of the electromagnetic spectrum?
• What is the Herzsprung-Russell Diagram? (H-R) Draw an H-R diagram and label carefully the various portions of the diagram where stars "cluster." What information can we deduce about how stars evolve, the most common types of stars, sizes of stars, ... from the H-R diagram (directly and when coupled with other information, such as the blackbody laws)? What are Main Sequence Stars? Which phase of stellar evolution is the most long-lived? What types of stars are the most common, the brightest ones or the faintest ones? What types of stars are the most common, the most massive ones or the least massive ones. Where do you find the largest stars in the H-R diagram? The smallest stars?
• What is the Russell-Vogt theorem? State the Russell-Vogt theorem. What is the most important stellar parameter?
• How does the luminosity of a star depend on its mass? How does the lifetime of a star depend on its mass? Which stars have the longest lifetimes, luminous V stars or faint V stars? massive Main Sequence stars or low mass Main Sequence stars? O V stars or M V stars? cool Main Sequence stars or hot Main Sequence stars?