Astronomy 12 Test Review KEY Chapters 5, 17 & 18

February 19, 2018 | Author: Anonymous | Category: Science, Astronomy
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Astronomy 12 Test Review KEY Chapters 5, 17 & 18-22 Multiple Choice Questions: 01. Light has a particle nature, and these particles are called photons. Which region of the electromagnetic spectrum has the lowest energy photons? (a) gamma ray (b) ultraviolet (c) visible (d) infrared 02. A source of light moves away from you. According to the Doppler effect (a) the frequency of the light will increase. (b) the frequency of the light will decrease. (c) the velocity of the light will decrease. (d) the velocity of the light will increase. 03. The spectral classification of a star is closely related to the star’s (a) brightness. (b) luminosity. (c) surface temperature. (d) distance. 04. How does the H-R diagram help astronomers identify stars? (a) It plots a star’s mass and core temperature, which allows astronomers determine the colour and region of where star is formed. (b) It plots a star’s luminosity and spectrum, which allows astronomers determine the size of the star. (c) It plots a star’s luminosity and surface temperature, which allows astronomers determine the type of star, size of star, and the star’s stage of evolution. (d) It plots a star’s size and surface temperature, which allows astronomers determine its region of origin. 05. What is the Main Sequence? (a) The evolutionary path, as seen on the H-R diagram, that a star follows throughout its life. (b) The region on the H-R diagram where, once they are formed. new stars rest for most of their lives. (c) The sequence of events a star follows from its formation to supernova. (d) The region on the H-R diagram where protostars first appear. 06. Define hydrogen burning. (a) The formation of a hydrogen gas cloud, also known as a nebula. (b) The chemical combustion of hydrogen. (c) the separation of the hydrogen envelope to form a planetary nebula. (d) The formation of helium by fusing hydrogen together. 07. When a star’s gravitational force pulling inwards and its internal pressure pushing outward are balanced, it is considered to be in what? (a) Hydrostatic equilibrium (b) Supernova (c) Structural Balance (d) Proton-proton fusion 08. What is a helium flash? (a) The rapid fusion of helium in a red giant’s core. (b) An explosion that creates a planetary nebula. (c) A type of solar flares that occurs on the surface of sun-type stars. (d) A flash of white light that occurs when a star collapses into a white dwarf. 09. What is a planetary nebula? (a) The destroyed remains of a planetary solar system when a sun-type star expands to a red giant. (b) The ejected envelope of a red giant that was formed from a sun-type star. (c) The disk of material around a protostar that will eventually form planetary system. (d) The initial massive gas cloud that stars and planets are formed from. 10. A white dwarf found in a binary system suddenly brightens, settles back down in a few months, and has the possibility to repeat. What is this called? (a) Red Giant (b) Carbon-detonation supernova (Type One) (c) Planetary nebula (d) Core collapsing supernova (Type Two) 11. Low-mass protostars evolve into main-sequence stars (a) less quickly than high-mass protostars because their weaker gravity slows their collapse. (b) less quickly than high-mass protostars because their higher core temperature slows their collapse. (c) more quickly than high-mass protostars because their stronger gravity speeds up their collapse. (d) more quickly than high-mass protostars because their higher core temperature speeds up their collapse.

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Short Response Questions: 12. Why do astronomers rely so heavily on electromagnetic radiation when studying astronomical objects? Since we cannot travel to virtually any astronomical objects we’d like to study, we depend on the electromagnetic radiation emanating from those objects that arrives at our telescopes on Earth (and orbiting Earth) to provide clues about what is happening in and around those objects.

13. How do the different regions of the electromagnetic spectrum differ from each other? What characteristic is the same among them? Regions of the EM spectrum differ in terms of their energy, wavelength, and frequency. All forms of EM radiation travel at the speed of light. 14. How does an emission spectrum of an element differ from its absorption spectrum as seen in a star? An emission spectrum is formed by a series of colored lines in exactly the same position (wavelength) as their corresponding dark lines in the absorption spectrum. 15. How do astronomers determine an object’s color and temperature? Astronomers use spectra and filters to determine the colors and temperatures of objects. An object’s temperature is related to its color by Wien’s Law (λpeak = 0.0029 Nm/T). When viewing objects through filters, relative temperature can easily be determined. A redder, cooler object will appear bright through a red broadband filter and dim through a blue filter. Similarly, a bluer, hotter object will appear bright through a blue filter and dim through a red filter. 16. Sketch an H-R diagram. Indicate the following regions: a. white dwarf stars b. main sequence white stars c. red giant stars g. blue supergiant stars

17. A star has a surface temperature of 10 000 K. What is the peak wavelength (in meters) of light emitted from the surface? SHOW ALL WORK & CALCULATIONS Use Wein’s Law max = (0.0029 Km)/T = (0.0029)/(10000 K) = 0.00000029 m = 290 nm (blue light) 18. Describe at least three properties of a star that an astronomer can deduce from its spectrum. (1) chemical composition, from the presence of the characteristic spectral lines of certain elements; (2) temperature, from spectral type; (3) star’s speed toward or away from us, from Doppler shift of the lines; (4) density, axial rotation, and surface magnetic fields, from line shape and width. 19. If a red star and a blue star have the same radius and brightness, which one is farther from Earth? Explain why. Because the stars have the same radius, the lower-temperature red star (using Wein’s law) must be nearer (using Stefan-Boltzmann law) in order to have the same apparent brightness as the higher-temperature blue star. 20. If a red star and a blue star have both appear equally bright and both are the same distance from Earth, which one has the larger radius? Explain why. Because the stars are the same brightness and distance from Earth, the lower-temperature star (using Wein’s law) red star must be larger (using Stefan-Boltzmann law) in order to have the same brightness as the highertemperature blue star. 21. Describe the proton-proton chain fusion in stars. In nuclear fusion, in the core of stars under enormous pressure and high temperature (over 10 million degrees K), 4 atoms of hydrogen are converted to a single atom of helium accompanied by a release of energy. At higher temperatures and pressures, larger atoms can fuse to form carbon, oxygen, and other heavier elements.

22. What are three significant differences between the evolutionary stages of low- and high-mass stars?

Most of the differences between low- and high-mass stars occur after the stars are on the main sequence. Differences: • High-mass stars use CNO cycle for H fusion while on the main sequence. • Low-mass stars have much longer main-sequence lifetimes. • High- mass stars evolve quickly through their stages of fusion until iron is produced in their cores. Lowmass stars never have internal temperatures rise to the point where carbon can fuse. • Low-mass stars end their lives quietly as white dwarfs. • High-mass stars end their lives in spectacular fashion by blowing up (supernova). • Low-mass stars can never explode or produce neutron stars and black holes. 23. What happens inside the core of a star the moment before a supernova explosion? What are the three possible outcomes or objects produced of this event?

Moments before a star explodes, it produces iron which drains energy from the core and precipitates the collapse of the star. Depending on the mass of the star three outcomes are possible: 1) the explosion sends all of the stellar material into space, 2) a neutron star can form, or 3) a black hole can form. 24. Complete tree diagram to the right: describe the two types of supernovas.

Supernova

Type I – Carbon Detonation

-lack H lines in spectra -can be formed from WD in binary system or supergiants with H/He removed -found everywhere in Galaxy -produced from old, low-mass stars -fixed maximum brightness

Type II – Core Collapsing

-have H lines in spectra -formed from young, massive stars -observed in arms of spiral galaxies -end result: NS or BH -stay brighter longer, with variable maximum brightness  brightness decreases rapidly

25. Complete table below: For each STAGE, write the letter of its STAGE DESCRIPTION in the corresponding blank. See #7 as an example.

H-R Diagram

Stage (7 to 14)

Stage Description

7. ___F___

A. B. C. D.

8. ___I___ 9. ___C___ 10. ___D___ 11. ___L___ 12. ___B___

E. F. G. H. I.

13. ___M___ 14. ___A___

J. K. L.

M.

Black Dwarf Planetary Nebula Helium Flash Carbon core expands and star returns to a balance state. Supernova New Star Oxygen fusion Carbon burning Forms a helium core as it leaves the main sequence Protostar Fragmentation Carbon core contracts and star climbs Giant branch again. White dwarf

26. Explain the general formation of a sun-type star (i.e. Steps 1-6).      

Stage 1: Fragmentation of Nebula  with sufficient mass, nebula fragments repeatedly under gravity Stage 2: Fragmentation Stops  lower-mass fragments form until internal gas pressure greater than gravity and fragmentation stops; thin fragment with hot center Stage 3: Formation of a Protostar  protostar and protoplanetary disk form; heat and light from gravitational energy at the core produce YSO (no fusion) Stage 4: Can be Seen on H-R diagram  no fusion but gravitational collapse produces sufficient surface temperature and luminosity to be measured on H-R diagram Stage 5: Violent Surface Activity  due to increasing core pressure from gravity, core traps heat that is released from time to time, causing violent surface activity Stage 6: Helium Core is Formed  core temperature sufficient to produce proton-proton fusion and helium deposited in core

27. Complete the Venn diagram to the right in order to compare the history of high mass stars with low mass stars (Hint: think the formation, evolution and death of the different stars).

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