Study Guide 2

                    Astronomy 105
                Study Guide - Exam II

I.  Light
    A.  Velocity
        1.  All observers get same value
        2.  Light requires no medium
        3.  c is the highest velocity possible
    B.  Wavelength
        1.  Order of Electromagnetic Spectrum (wavelength
            increases) Gamma, X-rays, Ultraviolet, Visible,
            Infrared, Radio
    C.  Wave equation
        speed of light = (wavelength) (frequency)
    D.  Doppler Effect
        1.  Small wavelength shifts of spectral lines due to
            radial velocity of light source
    E.  Production of light (Bohr model)
        1.  Electrons exist in stable orbits
            a.  increasing energy for larger orbits
        2.  Transitions can be made only if the precise
            amount of energy is received/emitted.
        3.  Energy contained in light related to its
            frequency  E = hf.
        4.  Frequency can be converted to wavelength = c/f
        5.  Wavelength is identified with color.
        6.  Atoms can only emit certain precise colors.
        7.  Every element produces characteristic set of
            colors.

II. Types of Spectra
    A.  emission - hot, tenuous source
    B.  continuous - hot, dense source
    C.  absorption - hot, dense source with cooler, tenuous
        gas above (star)

III. Spectral Lines  
     Information gained from their study:

  Property of Star          How it is Determined
************************************************************
Chemical composition      Identify lines in spectrum with
                          elements - But recall that
                          temperature affects how prominent
                          a line is.

Temperature               Relative strengths of lines
                          present in spectrum

Pressure (gravity)        Widths of lines (wide for normal
                          size stars, narrow for giants)

Velocity - Rotation Rate  Doppler Effect

IV. The Continuum
    A.  Blackbody Curves
        1.  Know how they are obtained, how they change from
            star to star, and how this is used to get
            temperature.

V.  Telescopes
    A.  Gather Light (see fainter objects)
    B.  Magnify (see more detail)
    C.  Resolution
        1.  Diffraction of telescope tube
        2.  Earth's atmosphere
            a.  "seeing"
            b.  Transparency

VI. Refractors
    A.  Major aberrations
        1.  Chromatic - colors do not have single focus
        2.  Spherical - rays entering different parts of
            lens have different foci
        3.  Both of these minimized by long focal lengths
        4.  Achromatic lens eliminated both major
            aberrations
    B.  Problems of Large Refractors
        1.  Support at edges only
        2.  Imperfections in glass
        3.  Absorption of light in glass


VII. Reflectors
    A.  No chromatic aberration
    B.  Parabolic shape means no spherical aberration
    C.  Can be large
        1.  Support from behind
        2.  Only surface of mirror must be good
    D.  Refractors preferred until aluminization process
        made reflectivity of mirrors high
    E.  Types
        1.  Prime focus
        2.  Newtonian
        3.  Cassegrain

VIII. Atmosphere of Earth
    A.  Permits viewing in visual, some IR, and radio only
    B.  Satellite advantages
        1.  Above turbulence
        2.  Observe entire E-M spectrum

IX. Charting the stars (know the concepts below)
    A.  Stellar Magnitudes
        1.  Apparent (m)  Absolute (M)
    B.  Spectral Type
    C.  Parsec
    D.  H-R Diagram
        1.  Plot of Absolute Magnitude vs. Spectral Type
        2.  Luminosity classes
        3.  Make comparisons between stars
            a.  size
            b.  temperature
            c.  brightness
    E.  Color Index
        1.  How does it relate to stellar temperature?

X.  Distance determining techniques (know how each is used
    to derive distance)
    A.  Stellar parallax
    B.  Spectroscopic parallax
        1.  Obtain spectrum of star and its apparent
            magnitude
        2.  Classify the spectrum by spectral type and
            luminosity class
        3.  Place star on the H-R Diagram
        4.  Read off the Absolute Magnitude
        5.  Using m and M calculate distance
    C.  Cepheid variables
        1.  Observe the light curve of a Cepheid
        2.  Determine average magnitude (apparent) and
            period
        3.  Use Period-Luminosity diagram to get M
        4.  Using m and M calculate distance
    D.  RR Lyrae variables
        1.  Observe the light curve of an RR Lyrae
        2.  Determine average apparent magnitude
        3.  All RR Lyrae variables have M = 0.5
        4.  Use m and M to calculate distance

XI. The Binary Stars
    A.  Only method of determining mass and radius for stars
    B.  Visual binaries
        1.  Can resolve both stars and record orbit
            a.  Stars must be nearby or widely separated
            b.  Orbital period of decades to centuries
    C.  Spectroscopic binaries
       1.  Periodic shifting of spectral lines allows
           discovery of binary nature
       2.  Periods must be short (high orbital velocity) to
           be discovered - orbital periods of days
    D.  Eclipsing binaries
        1.  Periodic light variations
        2.  Short orbital periods make eclipses more
            probable
    E.  Astrometric binaries
        1.  Detected by wobbly motion of a star across the
            sky