Quiz 2 Review.doc

1. What is a spectroscopy? Explain how astronomers might use spectroscopy to determine the composition and temperature of a star. a. Spectroscopy: the study of spectral lines produced by different substances; the analysis of the ways in which matter emits and absorbs radiation. b. First and astronomer must use a spectroscope to split a beam of radiation into its component frequencies and to deliver them to a screen for detailed study. Then, using Kirchhoff?s three laws about the relationships among the three types of spectra- continuous, emission line, and absorption line, the astronomer may determine the composition and the temperature of a star. 1. A luminous solid or liquid, or a sufficiently dense gas, emits light of all wavelengths and so produces a continuous spectrum of radiation. 2. A low-density, hot gas emits light whose spectrum consists of a series of bright emission lines that are characteristic of the chemical composition of the gas. 3. A cool, thin gas absorbs certain wavelengths from a continuous spectrum, leaving dark absorption lines in their place, superimposed on the continuous spectrum. These lines are characteristic of the composition of the intervening gas- they occur at precisely the same wavelengths as the emission lines produced by that gas at higher temperatures. 3. What is a continuous spectrum? And absorption spectrum? a. Continuous Spectrum: spectrum in which the radiation is distributed over all frequencies, not just a few specific frequency ranges. A prime example is the blackbody radiation emitted by a hot, dense body. b. Absorption Spectrum: the spectrum in which dark absorption lines occur in an otherwise continuous bright spectrum, where light within one narrow frequency range has been removed. 5. What is a photon? a. Photon: an individual packet of EM energy that makes up electromagnetic radiation. 6. In the particle description of light, what is color? Color of lines is also known as the frequency or wavelength of the lines. 8. Give a brief description of a hydrogen atom. A hydrogen atom consists of an electron with a negative electrical charge orbiting a proton carrying a positive charge. The proton forms the central nucleus of the atom. The equal an opposite charges of the proton and the orbiting electron produce an electrical attraction that binds them together within the atom. 9. What does it mean to say that a physical quantity is quantized? If a quantity is quantized, it means that the energy states (or orbitals) of the electron are behaving in a discontinuous manner; however, in the atomic realm, this behavior is the norm. Quantization: the fact that light and matter on small scales behave in a discontinuous manner, and manifest themselves in the form of tiny ?packets? of energy called quanta. 11. Why do excited atoms absorb and re-emit radiation at characteristic frequencies? Like the absorption spectrum, the emission spectrum is characteristic of the gas, not the original beam. Absorption and emission spectra are created by the same atomic processes. They correspond to the same atomic transitions. They contain the same information about the composition of the gas cloud. 12. How are absorption and emission lines produced in a stellar spectrum? What information might absorption lines in the spectrum of a star reveal about a cloud of cool gas lying between us and the star? When cool gas is placed between a source of continuous radiation and a detector, the resulting spectrum consists of a continuous spectrum crossed by a series of dark absorption lines. These lines are formed when the intervening cool gas absorbs certain wavelengths (colors) from the original beam of light. The absorption lines appear at precisely the same wavelengths as the emission lines that would be produced is the gas were heated to high temperatures. 14. Explain how a beam of light passing through a diffuse cloud may give rise to both absorption and emission spectra. The beam contains photons of all energies, but most of them cannot interact with the gas. All other photons in the beam do not interact with the gas at all, but pass through it unhindered. Photons having the right energies are absorbed, excited the gas, and are removed from the beam. The excited gas atoms return rapidly to their original states, each emitting one or more photons in the process. Some of the original energy is channeled into photons with energies associated with many different colors and moving in many different directions. One detector looking at the cloud from the side would record the re-emitted energy as an emission spectrum. Like the absorption spectrum, the emission spectrum is characteristic of the gas, not of the original beam. 16. How do molecules produce spectral lines unrelated to the movement of electrons between energy levels? Changes in molecular vibration produce infrared spectral lines. Changes in molecular rotation produce spectral lines in the radio part of the electromagnetic spectrum. 17. How does the intensity of a spectral line yield information about the source of the line? The complexity of atomic spectra generally reflects the complexity of the atoms themselves. By looking at the spectral line, one can tell what molecules were responsible for creating the spectrum, because each molecule has a given spectral line. The intensity of a spectral line can help the observer identify the amount or the electrical discharge of the element that cast the line. Therefore, we can change the intensity of lines by altering the amount of an element, such as hydrogen, or by changing its electrical discharge. 18. How can the Doppler Effect cause broadening of a spectral line? Atoms moving randomly (a) produce broadened spectral lines as (b) their individual red-shifted and blue-shifted emission lines merge in our detector. The hotter the gas, the greater is the degree of thermal broadening. So, if an atom happens to be moving away from us as it emits a photon, that photon is red-shifted by the Doppler Effect- we do not record it at the precise wavelength predicted by atomic physics, but rather at a slightly longer wavelength. 1. Cite two reasons that astronomers are continually building larger and larger telescopes. Astronomers build larger telescopes, because: a. They have a greater collecting area. b. They have finer angular resolution 2. List three advantages of reflecting telescopes over refractors. a. A reflecting telescope uses a mirror to focus the incoming light, relying on reflection (as opposed to using a lens and relying on refraction as the refractors do). b. As light passes through the lens of a refractor, some of it is absorbed by the glass. c. The lens of a refractor is quite heavy. Because it can only be supported around the edge, the lens tends to deform under its own weight. d. A lens has two surfaces that must be accurately machined and polished- a task that can be difficult. 3. What and where are the largest optical telescopes in use today? a. Mauna Kea Observatory in Hawaii (UK, France, Canada, and US telescopes) b. The Hubble Telescope in Space 4. How does Earth?s atmosphere affect what is seen through an optical telescope? Rays of light from distant space objects are deflected slightly as they pass through Earth?s turbulent and dirty atmosphere and into a telescope on Earth. 5. What advantages does the Hubble Space Telescope have over ground-based telescopes? List some disadvantages. Advantages: a. The Earth?s atmosphere is not interfering with the image relayed to the telescope. b. Disadvantages: a. The telescopes in space are smaller than those on Earth. b. 6. What are the advantages of a CCD (charged-couple device) over a photograph? a. Much more efficient than a photograph (CCD records 90% of the photons compared to the 5% of the photograph) b. Produces the picture in a digital format that can be transmitted easily. 7. What is image processing? Image processing takes out the background noise (anything that corrupts the integrity of the message). 10. How do astronomers use adaptive optics to improve the resolution of telescopes? Astronomers improve the resolution of the telescopes by undoing the effects of atmospheric turbulence using an approach known as adaptive optics (deforming the shape of a mirror?s face under computer control while the image is being exposed). 12. Which astronomical objects are best studied with radio techniques? Astronomical objects that cannot be seen or observed using other instruments are the ones that are best studied using radio techniques. 19. What are the main advantages of studying objects at many different wavelengths of radiation? Multi-wavelength observations can complement one another, greatly extending our perception of the dynamic universe around us. 1. Name and describe all the different types of objects found in the solar system. Give one distinguishing characteristic of each. Include a mention of interplanetary space. The solar system consists of the Sun and everything that orbits it, including the nine major planets, the moons that orbit them, and the many small bodies found in interplanetary space. a. Sun: mildly large, extremely hot star b. Nine Planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto c. Planetary Moons: orbit individual planets d. Interplanetary Space: includes all the space the solar system exists in which may include comets, asteroids, meteoroids, and space debris. 2. What is comparative planetology? Why is it useful? What is its ultimate goal? Comparative Planetology: the systematic study of the similarities and differences among the planets, with the goal of obtaining deeper insight into how the solar system formed and has evolved in time. It is used for comparing and contrasting the properties of the diverse worlds we encounter. Its ultimate goal is to understand the conditions under which planets form and evolve. 4. List some ways in which the solar system is an ?orderly? place. a. All of the planets orbit the sun counter-clockwise. b. All of the planets? orbital pathways are ellipses with the Sun at or very near one focus. c. The distance between the planets gets larger as the planets get farther from the Sun. 6. Which are the terrestrial planets? Why are they given that name? a. The four inner most planets are the terrestrial planets (Mercury, Venus, Earth, Mars). b. The word terrestrial derives from the Latin word terra, meaning ?land? or ?earth.? 9. Compare the properties of Pluto in table 6.1 with the properties of terrestrial and Jovian planets given in table 6.2. What do you conclude about the classification of Pluto as either a terrestrial or Jovian planet? a. Pluto is closer in mass and radius to the terrestrial planets. It also is predominantly rocky, has a solid surface, has a slow rotation, has a weak magnetic field, has few moons, and no rings which all make it more similar to the terrestrial planets. b. Pluto should be classified as a terrestrial planet. 10. Why are asteroids and meteoroids important to planetary sciences? Asteroids and meteroids provide the keys to answering some very fundamental questions about our planetary environment and what the solar system was like soon after its birth. 13. How and why do scientists use gravity assists to propel spacecraft through the solar system? a. Gravity Assist: using gravity to change the flight path of a satellite or spacecraft; a gravitational slingshot or swing-by is the use of the relative movement and gravity of a HYPERLINK "http://en.wikipedia.org/wiki/Planet" \o "Planet" planet or other celestial body to alter the path and speed of HYPERLINK "http://en.wikipedia.org/wiki/Spacecraft" \o "Spacecraft" spacecraft . b. Typically gravity assist is used in order to save fuel, time, and expense. c. It can be used to decelerate a spacecraft (useful when traveling to an inner planet) or accelerate a spacecraft (useful when traveling to an outer planet) 14. Which planets have been visited by spacecraft from Earth? On which ones have spacecraft actually landed? a. Planets visited by spacecraft from Earth: Mercury, Venus, Mars, Jupiter, Saturn, Uranus, and Neptune b. Planets spacecraft landed on: Venus and Mars 15. Why do you think Galileo and Cassini took such circuitous routes to Jupiter and Saturn, while Pioneer and Voyager did not? Galileo and Cassini are the more recent spacecrafts. They were using the various planets? gravitational pulls to helps propel them to their destinations. It conserved gas and utilized free energy from the other planets orbits and increased the speed at which they reached their targets. 17. What is the key ingredient in the modern condensation theory of the solar system?s origin that was missing or unknown in the nebular theory? Interstellar dust in the solar nebula: dust in between the stars 18. Give three examples of how the condensation theory explains the observed features of the present day solar system. a. Small clumps of matter grew by accretion, gradually sticking together and growing into moon-sized bodies whose gravitational fields were strong enough to accelerate the accretion process, subsequently causing the bodies to grow into proto-planets. b. The temperature in the solar nebula determined which materials could condense out and hence also determined the composition of any planets forming there. Ultimately, this led to the observed differences in composition between the inner and outer solar system c. When the Sun became a star, its strong winds blew away any remaining gas in the soalr nebula. Leftover small bodies that never became a part of a planet are seen today as the asteroids and comets.