This review covers these topics:
Radiation Laws, Atoms and Molecules, Telescopes, Light Detectors, Space Astronomy, Experimental Astronomy, the Solar System, Planetary Exploration.

Use these pages as a study guide-- i.e., a list of terms, concepts, and relationships that you will want to understand for the exams. This sheet is NOT a synopis of the class notes or textbook. A few sample questions, some 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 !

There are many terms and expressions whose definition you need to understand. Use the chapter reviews in the text, where many terms are highlighted, and also those terms specifically described in your class notes.

Electromagnetic Spectrum:

• 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 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 ?

• 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 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/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/or record 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.

• Know the ordering of the planets from the Sun.
• Know which planets are the terrestrial planets, which are the jovian planets, and which fit neither category.
• Be aware of and understand the primary differences between terrestial and jovian planets. Use Table 6.2 in your textbook.
• Know the approximate relative sizes and masses of the planets. Look at the appropriate columns in Table 6.1.
• Understand the term "density", and be able to compare the average densities of the planets (see "DENSITY" in TABLE 6.1)
• Know the approximate rotational period of the planets -- know which are "slow", which are "medium", and which are "fast" rotators.
• Understand the physical differences between comets, asteroids, and meteroids.
• Know which planets have been visited by spacecraft and on which objects have spacecraft actually landed. Develop a sense of how each planetary exploration mission changed our perspective and understanding of the properties of each planet. Q? What did Magellan add to our knowledge of Venus ?? What about Viking with respect to Mars ?

For each planet be aware of their basic characteristics and how those characteristics compare with those of the other planets (at the level discussed to this point in the semester).

• Atmospheres: Which of the terrestrial worlds have one, which don't ?
  • Mercury: no atmosphere
  • Venus: dense, hot, atmosphere, 96% CO₂.
  • Earth: nitrogen/oxygen atmosphere, weather, precipitable H₂O
  • Moon: no atmosphere
  • Mars: dry, thin, cold atmosphere, 95% CO₂.
• Surface appearance and relevant processes: Q? Which planets are heavily cratered ? Which have volcanoes ? Which have liquid water ?
• Which have moons ? Which do not ?

Radiation & Spectra:

• 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.
• 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 redshift and those which produce a blueshift.
• 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.
• 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.
• Understand how astronomers use the information in spectra to explore the properties of objects in space-- their temperature, radial motions, rotation, chemical composition, etc.

• 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.
• What is a digital image and how does it differ from a photographic image ?
• Review the types of devices used by astronomers to record images and spectra from space.

• 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 physically substantially larger than telescopes which work in the optical part of the spectrum.

• Be able to describe the solar system in general terms: contents, shape, size. What type of orbits do the planets mostly exhibit ? Any oddballs ?
• Be cognizant of how various planetary properties are actually determined by astronomers:
  • Mass - by applying Newton's laws of motion and gravity
  • Size - knowing the distance, and the angular size, and appplying the small angle formula
  • Distance - by radar ranging, applying Kepler's laws, and direct communication with spacecraft.
  • Density
  • Rotation rate
  • Orbital period
• Be able to outline the stages of planetary exploration, in a historical sense, and know about what missions are currently ongoing.