AST 1002: Outline for Topic D

[Sections Taught by Prof. H.L. Cohen]

Site Map • Prof. Cohen • Department of Astronomy • University of Florida

Last updated January 1, 2003

Home Page

Course Information

Study Guide

Chaisson Textbook

Other Resources

Alachua Astron. Club

Undergrad. AstroPhy. Soc.

---

Examples

Figures

Other

Outlines

PowerPt

Tables

---

Topic D: Star Light (EM Radiation)

• Electromagnetic (EM) Spectrum (Ref. Table 8)
  • Definitions: spectrum, wavelength, frequency
  • Types of EM radiation by wavelength, frequency or energy (gamma rays, X-rays, etc.)
  • Types of visible light by wavelength, frequency or energy (violet, indigo, blue, etc.)
  • How does the size of red waves (i.e., their wavelengths) compare to violet waves?
  • Wavelengths that Earth's atmosphere transmits (and blocks) — i.e., the "windows"
  • Does speed of E-M radiation (in a vacuum) depend on wavelength?
  • Know approximate value of speed of light (in both mi/sec and km/sec)
  • Know approximate time (minutes) for E-M radiation to travel one astronomical unit
  • Be able to compute distances or times to solar system objects from speed of radiation
    (Ref. Topic D, #15–17)
    
  • Know approximate value for speed of sound at sea level (in both feet/sec and miles/hr)
  • Know number of feet in a mile
  • Be able to estimate the distance of a thunderstorm (Ref. Topic D, #13–14)
  • Examples of forms of energy often confused with E-M radiation (e.g., sound & heat)
    (What do UF astronomers sometimes do that may confuse radio and sound?)
• Instrumentation (Detectors) (See Table 8b and Table 8c)
  • Names and purpose (i.e., function or use) of each type
    –Human eye (know color of peak sensitivity) — Table 8b, #1
    –Photographic plates and films — Table 8b, #2
    –Charged Couple Device or CCD — Table 8b, #3
    –Photoelectric photometer — i.e., photomultiplier tube — Table 8b, #4
    –Spectrograph — Table 8b, #5
  • Definitions: dispersion, refraction, diffraction, spectrograph, spectrum (see Table 8c)
  • Be able to distinguish between spectrograph, spectrum, spectrogram, spectroscopy and spectroscopist (see Table 8c)
  • Spectrograph (Ref. Fig. 5)
    –Parts of a spectrograph (slit, collimator, prism or grating, camera)
    –Function (purpose) of each part of a spectrograph (i.e., what each part does)
    –What determines the basic shape of a spectral line?
    –What is a comparison spectrum?
• Types of Spectra (Ref. Fig. 6)
  • Names and appearance of the four types of spectra in Study Guide Figure 6
  • Types of sources producing each type (e.g., solids, liquids or compress gases produce continuous spectra, etc.)
  • Some example sources for each type of spectrum above — Ref. Topic D, #23 (e.g., continuous spectra produced by tungsten light bulb filaments, molten iron, etc.)
  • Information each type of spectrum potentially can provide (e.g., line spectra allow chemical identification of elements, etc.)
  • What type of spectrum does Sun produce?
  • What type of spectrum do most stars produce?
  • What do absorption line spectra of stars imply about the basic structure of a star?
  • Hence, which part of a star produces the absorption lines in its spectrum?
• Temperature Scales
  • Names of the three basic scales
  • How does the size of a degree compare between the three scales?
  • Where zero degrees counted from for each scale?
  • Know freezing and boiling points of water on each scale
  • Know meaning of absolute zero
  • Approximate relation between the three scales at high temperatures
  • Approximate temperatures (in Kelvins) of both Sun's surface and your environment
• The Radiation Laws (Ref. Fig. 7)
  • What is a black body (BB)
  • Plank's Law and BB Radiation (Ref. Fig. 7, Item 1)
    –What Planck's Law tells you
    –Be able to characterize BB radiation if the object is cool (room temperature)
    –Be able to characterize BB radiation if the object is very hot
    –Hence, what happens to a BB's radiation when heated?
    
  • Wien's Law (both qualitatively and quantitatively; Ref. Fig. 7, Item 2)
    –What happens to wavelength of radiation peak of BB curve if temperature changes
    –Know mathematical form of Wien's Law
    –(i.e., Wavelength of Radiation Peak inversely proportional to 1 / Temperature)
    –Know how to calculate temperature (or wavelength of peak) using Wien's Law (Ref. Example 3; also Topic D Questions #32–37, #45)
  • Stefan-Boltzmann's Law (both qualitatively and quantitatively; Ref. Fig. 7, Item 3)
    –What happens to total energy radiated over entire spectrum if temperature changes
    –Mathematical form of Stefan-Boltzmann's Law (i.e., E_Total proportioanl to T⁴)
    –Know how to calculate temperature (or total energy emitted) using Stefan-Boltzmann's Law (Ref. Example 4; also Topic D Questions #38–45)
  • How color of a BB changes when temperature increases
  • Know the range of colors for stars (Ref. Table 11, next-to-last column)
  • What is Sun's color? Also know approximate surface temperature of Sun (in Kelvins)
• Tentative List of Study Guide Questions To Omit for Topic D
  • Do all questions
  • Omit none

---

* This list is reasonably complete but students remain responsible for all material presented in class. Tables, figures, examples, etc., listed here refer to Study Guide items.

[Return to Top]

---

Recommended web browser to view this site is Netscape Navigator 4.0 (or above) with video display supporting at least 256 colors.
High color (16 bit) or true color (24 bit) display is preferred.

---

---

For comments and suggestions contact Howard L. Cohen at cohen@astro.ufl.edu About this site (department disclaimer and recommended web browser) © Copyright 1999-2003 Howard L. Cohen