This review covers these topics:
Light & Radiation, the Electromagnetic Spectrum, Radiation Laws, Atoms & Molecules, Spectra of Celestial Objects, Telescopes, Light Detectors, Space Astronomy, Experimental Astronomy, The Sun, Solar Activity & Solar Power

Use these pages as a study guide-- i.e., a list of terms, facts, concepts, and relationships that you will want to understand for the exams. This review is NOT intended as a synopis of the class notes or textbook. Rather, it mixes some factual information with lists of items that students should review. Sample questions, some given with answers, some without, are included. These are indicated with a preceding "Q?" symbol.
This guide is not guaranteed to be comprehensive-- tests cover the text and notes !

Waves and Wave Motions:
Light and other forms of radiation can be defined in terms of waves. Understand these terms and how they relate.

• wavelength - distance between peaks (crests) of a wave
• amplitude - intensity or height of a wave
• frequency - number of waves per second
• period - time between successive wave crests.

• Know the definition of the electromagnetic spectrum.
• Know the components of the spectrum and how they are ordered: gamma rays, X-rays, visible light, ultraviolet light, infrared light, radio waves, in order of increasing wavelength.
• High energy radiation means: small wavelengths, high frequency, and "blue" color.
• Low energy radiation means: large wavelengths, low frequency, and "red" color.
• Understand what is meant by a blackbody radiation curve.
• Temperatures in astrophysics are measured on the Kelvin scale. Kelvin temperature scale = degrees Celsius + 273.
• Wien's law - relates the peak of a blackbody spectrum to an object's temperature.
• Stefan's law - relates the total energy emitted by an object to its temperature.
• Doppler effect - relates the shift in the wavelength of spectral features to the line-of-sight velocity of an extraterretrial object. Know what a "spectral feature" is. Review how the amount of any shift is related to that velocity. What's the difference between a blueshift and a redshift ?

• Be able to visualize the spectrum of an object; use the figures in the text.
• Relate the patterns within an observed spectrum to the object producing the spectra.
• Define and understand how each of the following types of spectra are produced. Also, how are emission or absorption lines produced ?
  • continuous spectrum
  • emission line spectrum
  • absorption line spectrum

• Identify protons, neutrons and electrons. Q? Which are electrically charges, which are not ?
• Know the difference between protons, neutrons and electrons in terms of their relative masses.
• Where are these various particles located within an atom ?
• Be aware of the "atomic number", i.e., the number of protons in some common elements. Hydrogen atoms have 1 proton, uranium atoms 92. All other naturally occuring elements possess between 1 and 92 protons. Look at the Periodic Table of the Elements given in the Appendix of the text.
• Know the definition of an isotope and the periodic table.
• Electrons "orbit" an atomic nucleus in various energy levels. Understand the meaning of the term "energy level".
• Know what "ground state" implies with respect to electron energy levels within atoms.
• Understand what "ionized" implies-- the removal of 1 or more electrons from an atom.
• Atoms can combine to form molecules. What are some common, simple molecules ?

• Molecules are composed of 2+ atoms linked via the sharing of electrons.
• Know the chemical composition of some simple molecules, e.g., water, carbon dioxide
• Be aware of the added complexity concerning energy levels in molecules. In addition to their electron levels, molecules also rotate and vibrate.

• continuous spectra - temperature, energy rate
• emission line spectra - composition, velocity, rotation, temperature
• absorption line spectra - composition, velocity, rotation
• spectral measurements - wavelength, strength, width & wavelength shift of spectral lines

• Review the operating principles of both major types of telescope:
  • Reflectors use curved mirrors to collect & focus light and can be manufactured large. If the mirror is constructed incorrectly, it can suffer from spherical abberation.
  • Refractors use curves lenses to focus light, and are limited to sizes less than about 1 meter. Lenses, made of glass, suffer chromatic abberation -- the focal point of the lens is different for different wavelengths of light.
• Know the advantages and disadvantages to each basic telescope type.
• Telescope "size" is defined by the diameter of the objective: either a lens or a mirror.
• Know the meaning of light-gathering power and resolving power.
• All major research telescopes are of the reflecting type. Be aware of the different designs for these telescopes. How do astronomers get the light "out" of the telescope to study and make a record of it ?

• Know the basic methods astronomers employ to make astronomical observations.
• Images of the sky are constructed using a variety of technologies. Photographs are chemical recorders of information, CCD camers record light digitally in electronic form. Which is used more commonly today ?
• Astronomers use spectrographs to split the light of an object up into its component colors.
• Spectrograms provide information on a celestial object's temperature, composition, line-of-sight velocity, density, and luminosity. How ?

• Space-based telescopes are required to observe in many parts of the spectrum. Understand how the Earth's atmosphere interferes with astronomical observations from the Earth's surface.
• Understand the advantages and disadvantages of space-based telescopes vs those on the ground.
• Radio telescopes use large dish antennae to record radio waves from astronomical sources.
• X-rays and gamma-rays are much harder to collect and focus than optical light. Astronomers have constructed special devices to capture this type of radiation.

• What is a star ?   Review the basic definition of a star.
• Be aware of the the values of important parameters which describe the Sun.
  • Radius:   ~700,000 km   =   ~ 110 Earth radii
  • Mass:   2 x 10³⁰ kilograms   = ~ 332,000 Earth masses.
  • Surface temperature:   ~ 5800 K.
  • Rotation rate:   25-30 days, depending on latitude.
• Review the overall structure of the Sun, both the interior zones, and the regions which define the solar atmosphere. Be able to label a diagram with these zones.
• Be cognizant of the differences between the solar interior zones: the core, the radiation zone, convective zone, and photosphere. What defines each zone ?
• What is granulation ?
• Understand the basic attributes and physical properties of the solar atmosphere. What are the differences between the photosphere, chromosphere, and corona ?
• Understand the temperature and pressure profiles of the solar interior-- from 15 million K at the center, to ~6000 K at the surface.
• Be aware of the Sun's composition - the chemical makeup of the solar photosphere.

• Understand what is meant by solar activity. Solar activity manifests itself through a variety of phenomena: sunspots, prominences, flares, coronal mass ejections. Describe and understand the difference between these phenomena.
  • sunspots   How are they observed ?
  • prominences   Where are these seen on the Sun ?
  • flares  
  • coronal holes
  • active regions
• Know the basic phenomena associated with the solar activity cycle. Sunspot counts (the number of spots recorded each day), sunspot locations, the frequency and intensities of solar flares, etc all increase and decrease during the 11-year cycle.
• What is the solar wind ?

• The Sun produces energy (light) through the process of nuclear fusion. Know what is being "fused", and be familiar with the steps in the fusion process.
• Where does fusion occur within the Sun ?
• Neutrinos, subatomic particles produced in fusion reactions, radiate from the Sun and pass right through the Earth. Understand how the technically difficult problem of counting solar neutrinos resulted in an "undercount" compared to the standard solar model .

Electromagnetic Radiation:

• Electromagnetic radiation is the means by which energy (and information) is transmitted through space.
• Radiation travels in the form of waves.
• Understand the concept of a wave and how waves are described in terms of their length, frequency, period, and height.
• Understand the difference between electromagnetic waves which do not require a medium in which to propagate, and sound waves, which do.
• The electromagnetic spectrum runs from high-frequency, short wavelength, high energy gamma rays to low-frequency, long-wavelength, low energy radio waves.
• Understand why only specific types of radiation can pass through the Earth's atmosphere and be detected at the earth's surface. Also review which forms of radiation can reach the Earth's surface.
• Remember that ALL forms of electromagnetic radiation travel at the exact same speed, 3 x 10⁸ meters per second. This means that a long-wavelength signal such as radio waves travel at the same speed as a short-wavelength signal, such as X-rays.

• Understand what is meant by the spectrum emitted by an object.
• Be able to label a sketch of a spectrum, and understand what is displayed in such a sketch. What is plotted along the X-axis and along the Y-axis ?
• Review the concept of temperature. The temperature of an object measures the amount of microscopic motion within the object.
• What is blackbody radiation ? Know that the radiation emitted by a blackbody is described by a blackbody curve. Be able to plot a blackbody curve. What is another name for this curve ?
• Understand how the temperature of an object is related to its blackbody emission curve. Objects at at given temperature emit radiation at a range of wavelengths.

• Stefan's law: Hotter objects emit more energy. The rate of energy emission depends on temperature to the 4th power.
• Wien's law: The wavelength of peak emission is inversely proportional to temperature-- cooler objects have peak wavelengths that are smaller. Think about how this concept relates to the appearance of an object as its temperature is altered.
• The Doppler effect: Motion along the line-of-sight to an object alters the wavelength or frequency of its emitted radiation. Understand the conditions which produce a red shift and those which produce a blue shift.
• Visualize how each of these "laws" affects the spectrum of a object. What happens when (a) the temperature is increased or decreased, (b) the energy output increases or decreases, (c) the object's velocity changes ?

• Atoms have varying numbers of protons, electrons, and neutrons. Understand how the properties of an atom are defined by those varying numbers
  • The number of protons in an atomic nucleus determines the type of element.
  • The number of electrons determines the ionization state of an atom. How ?
  • The number of neutrons determines the particular isotope of that element.
• Understand and be able to describe the Bohr atomic model for hydrogen. How does Bohr's initial idea differ from our modern view of atomic structure ?
• Understand the energy level concept for how EM radiation (light, radio waves, X-rays) is emitted and absorbed by atoms & molecules.
  • An electron "jumps" to an excited state when it absorbs a photon with exactly the right amount of energy. Understand physically what happens in the atom when a photon is absorbed.
  • An electron can be "de-excited" (drop down a level) by emitting a photon, releasing energy.
  • Understand how the energy of an emitted or absorbed photon is defined by the difference in energy between two levels.
  • Understand why each different element (hydrogen, helium, carbon, etc) has its own unique emission/absorption spectrum, and how that spectrum is related to its pattern of energy levels.

• How is matter constituted as the temperature changes ? What causes the change in state as temperature changes ?
  • Cold - atoms form molecules, molecules link up into solids & liquids
  • Warm - some solids melt or evaporate into gases
  • Hot - molecules split into their constitute atoms, solids melt, liquids evaporate
  • Really hot - all molecules split apart, atoms begin to lose their electrons, matter becomes a plasma.
• Consider what states of matter might your find in different astronomical environments.

• Understand how astronomers use the information in spectra to explore the properties of objects in space-- their temperature, radial motions, rotation, chemical composition, etc.
• Many physical processes can cause spectral lines to be "broadened", in other words, appear to the observer to be wider than normal. Be cognizant of these processes, and how they affect the line width, via the Doppler effect.

• Understand how light is collected and focused by telescopes. Sketch the light "path", based on textbook illustrations.
• Understand why astronomical images are "blurred" by the atmosphere, and review some of the techniques used by astronomers to compensate for this blurring.
• Q?   What is a digital image and how does it differ from a photographic image ?

• Review the technique of interferometry. How does it help improve astronomical observations ?
• Why are computers essential to modern astronomical research ?
• Understand the fundamental importance of observations over the entire elecromagnetic spectrum. In the past 40 years, astronomers have moved from optical, then radio observations to the ability to explore the whole spectrum. Q?   How does radio and x-ray astronomy complement optical observations ?
• Understand why radio telescopes are substantially larger than telescopes which work in the optical part of the spectrum.

• Why is the Sun stable ?   What physical processes keep the Sun from collapsing under gravity or exploding due to its high temperature and pressure interior ?
• Understand the physical concept of convection. How does it apply to the Sun ?
• Understand why the corona of the Sun is hotter than the surface; 6000 K vs about 3,000,000 K. Astronomers believe that release of magnetic energy at the base of the solar atmosphere accounts for the heating of the corona.
• Review the reasons that solar eclipses provide unusual and scientifically useful observations of the solar atmosphere.
• How do astrophysicists explore the Sun ?   How is information gleaned about the solar interior and the solar atmosphere ?
• Helioseismology, a branch of solar physics, is the study of surface patterns on the Sun. Review the basis for and the usefullness of this subject. What exactly are the "patterns" visible on the Sun's surface ?   How does helioseismology permit us a view into the solar interior ?
• What is meant by the "Standard Solar Model" ?

• Why are sunspots dark compared to the surrounding solar disk ?
• Describe the source of the solar wind. How does material manage to escape the powerful gravitational field of the Sun ?
• Review ideas for the origin of solar activity-- what drives these phenomena ?   Most solar activity is powered by the tangling and untangling of lines of magnetic force.

• Q?: Why does the fusion process require high temperatures and pressures ?
• Q?: How does the fusion process produce energy ?
  ANS: The sum of the masses of 4 protons is greater than the mass of the helium nucleus into which those 4 protons fused. The excess mass is converted to energy, and emitted in the form of gamma rays.
• Energy is produced in the Sun's core via nuclear fusion. How does that energy "get out" to the surface and to us ?
• How do observations of solar neutrinos provide information about reactions deep in the Sun ?
• Solar neutrinos are measured at "observatories" that are very different than the traditional "telescope in a dome". Describe a solar neutrino observatory and detail why they are differently-enabled.
• In the last few years, an explanation for the solar neutrino problem appears to have been discovered. Define this "problem" and describe the explanation ?