Chapter 9 Exam Questions and Answers.docx

Chapter 9 Exam Questions and Answers 1. Why did all attempts to detect stellar parallax fail until the 1830s? There were many failed attempts to detect stellar parallax, owing to the incorrect assumption that the brightest stars are the nearest stars, they kept choosing stars that were not the closest ones so they couldn’t see any parallax 2. What did Halley announce about stars in the early 1700s? How did this discovery aid the detection of stellar parallax? a) Halley compared ancient star catalogues with current star positions and found 3 moving stars b) By the 1830s, stellar parallax was finally seen in the nearest stars, now chosen for their brightness and large motion (and preferably, widely-space binaries) 3. What is our nearest star, and how far away is it (approximately) in light years? The nearest star (Alpha Centauri) has a distance of 4.4 ly 4. What is the definition of a light year? What is the definition of a parsec? (NOTE: the specific values in km aren't necessary here). Which unit is bigger, and by approximately how much? a) Light year = A unit of astronomical distance equivalent to the distance that light travels in one year, which is 9.4607 × 1012 km b) Parsec = A unit of distance used in astronomy, equal to about 3.25 light years (3.262 light years) c) Parsec is bigger by approximately approx. 3 light years 5. According to the wave theory of light, what are all light waves composed of? Light waves are composed of oscillating electric and magnetic energy fields 6. Describe how a wave from a bright blue light source is different from a wave from a faint red light source. - A Wave from a bright blue source (high amplitude and short wavelength) - Faint red light source (low amplitude and long wavelength) - Wavelength decreases from red to blue (therefore, frequency increase from red to blue) 7. What colour of visible light is shortest in wavelength? What colour of visible light is longest in wavelength? What colour of visible light has the lowest frequency? What colour of visible light has the most energy? a) violet b) red c) red - lowest frequency with the lowest energy d) violet - the higher the frequency the higher the energy 8. In the full spectrum of light, what kind of light is shortest in wavelength? What kind of light is longest in wavelength? What kind of light has the most energy? a) Gamma Rays b) Radio waves c) Gamma rays 9. What is a spectroscope? Any of various instruments used to analyze the component parts of a sample by separating its parts into a spectrum. - Ex. passing sunlight through glass and observing the spectrum through a telescope 10. What is Fraunhofer’s Spectrum a spectrum of? What does it contain (ie., continuum emission, absorption lines, and/or emission lines)? a) It was the spectrum of sunlight, he used it to create the Frauhnhofer's Spectrum which contained ~600 thin dark lines, labeled with letters to designate their wavelength b) Absorption lines 11. Describe (briefly) how the chemical composition of a star can be determined. To determine the chemical composition of a star, you obtain its spectrum you split up its light, investigate its absorption lines and you match up those absorption lines with emission lines of known chemicals and that tells you what chemicals are in that atmosphere of whatever star you are looking at 12. What did Bunsen and Kirchhoff observe in the spectrum of sunlight combined with a gas flame? What was their correct explanation for this, and what did it cause them to predict about the Sun? How was their prediction proven in the 1860s? a) They found that the dark lines of the sun's spectrum got thicker b) They concluded: the Sun's core, which produces the full spectrum of light, is surrounded by a gas layer (a sodium atmosphere). Molecules in the Sun's atmosphere absorb light at their signature wavelengths, producing the dark lines ("absorption lines") c) The proof: during solar eclipses in the 1860s-70s, the spectrum of the Sun's atmosphere was produced, revealing the "emission lines" predicted by B&K 13. How did the element Helium get its name? 1868: Lockyer discovered a new emission line in the Sun's atmosphere and named it "Helium" (Helios = Greek god of the Sun). 14. In a graphical spectrum, what do emission lines appear as? What do absorption lines appear as? a) A graphical spectrum: peaks are emission lines b) Dips are absorption lines 15. What does the spectrum of a star contain (ie., continuum emission, absorption lines, and/or emission lines)? How about the spectra of a gas cloud, a star cluster, and a gas/star system? a) Star – absorption lines and has continuum emission lines b) Gas cloud - emission-line nebulae Star cluster – Continuum emission and absorption-lines Gas and Star systems - Continuum emission line (from stars) and absorption-line (from stars) and emission lines (from gas cloud) 16. Why was the element Oxygen originally named "Nebulium"? Professor Metcalfe’s full answer: Oxygen was already known of when this Nebulium line was discovered. Basically this element Nebulium was observed, these new emission lines were observed in a planetary nebula and they came from very hot oxygen. But it wasn’t known yet that hot oxygen produces these lines. So it was thought this was a new element and it was given a name Nebulium because it was first seen in a Nebula but later on they realized if you heat oxygen up to really high temperature you get the exact same line. Nebulium was not longer its own element, it was just oxygen. Simplified Lecture note answer: 1864: Huggins produced the spectrum of a planetary nebula. It contained unidentified emission lines. The lines were named 'Nebulium', until matched with Oxygen in the 1920 17. What does the spectrum of a planetary nebula contain (ie., continuum emission, absorption lines, and/or emission lines)? When Huggins discovered this, what did it prove about planetary nebulae (ie., what are they made of)? a) Planetary nebula (gas cloud = expanding gas from a dying star) – Emission lines b) Proved that it is a gas clouds (oxygen) 18. What is radial motion? How does it affect light waves? What is the name of this effect? a) Radial motion: Towards an observer or away from the observer b) If I am giving out light waves as I move towards you, the light waves are going to get compressed, as I move away from you the light waves are going to get stretched c) Doppler Effect 19. How does a light source's spectral lines reveal that the spectrum is redshifted? How about blueshifted? If a spectrum is redshifted, what does this tell us about the motion of the light source? How about if the spectrum is blueshifted? a) Its lines are going to be shifted to longer wavelengths and towards the red side - redshifted b) Its lines are going to be shifted to shorter wave length and towards the blue side– blueshifted c) Redshifted – the object is moving away from us d) Blueshifted- the light source is approaching us 20. What is astrophotography? Why does it allow us to see deeper into space than with the eye and telescope alone? Who was one of the pioneers of this? What sort of survey did he conduct? a) Astrophotography – attachment of a camera on to a telescope b) With a camera you can take long exposure photos and capture more light than with your eye c) Henry Draper d) Photographic spectroscopic survey of all visible stars. 21. What were the members of "Pickering's Harem" hired to do? To complete the Henry Draper Catalogue of spectra of over 225,000 stars. 22. What property of stars was used to place the spectral types in their original alphabetical order? What property of stars was used to re-arrange their order into their current order (O-B-A- F-G-K-M)? a) By the strength of the star’s Hydrogen lines. b) Annie Cannon: reduced and re-ordered the spectral types from blue to red (hottest to coldest): O-B- A-F-G-K-M. 23. What do we know about the chemical composition of the reddest stars, due to their numerous spectral lines? The reddest stars (K, M) have more metals than other spectral types. 24. If a star has a spectral type of B8, which type of star is it more similar to, O or A? The star is more similar to A 25. What is a photon? A photon is a particle of light (another way of representing light, like the wave) 26. According to the Bohr model of the atom, what are the 3 components of an atom? What determines an atom's chemical element? a) Atom = proton, neutron, electron b) The number of protons (p) determines an atom’s number of electrons (e-) and its chemical element; 1p1e = Hydrogen, 2p2e = Helium, etc. 27. Explain (briefly) what causes atoms to produce absorption lines. What about emission lines? a) When an e- absorbs a photon with the exact E (or lambda λ) it needs to get excited, e- jumps to a higher shell, causing an absorption line b) When an excited e- drops down a shell, it emits a photon with the exact E (or lambda λ) to return to ground state, causing an emission line 28. What unusual discovery did Cecilia Payne make about the chemical composition of stars? All stars are predominately composed of H (and He). 29. Describe how Eddington proved one of the predictions of Einstein's General Relativity theory. During a total solar eclipse, he proved General relativity by observing that when light rays pass near the Sun, their path is bent by the curved space around the Sun 30. What was Eddington and Bethe's correct explanation for the energy source of stars? Why does this process release energy? How does it explain why stars produce so much energy? How does it explain the existence of Helium in stars? How does it explain the full spectrum of light that we receive from stars? How does it explain the long lifetimes of stars? a) The energy from stars is produced from the fusion of Hydrogen nuclei into Helium at high temperatures (i.e. nuclear fusion) b) It releases energy because the mass of the ingredients is greater the mass of the product. The mass of 4 Hydrogen is greater than 1 Helium atom so this excess mass gets converted into energy according Einstein’s equation of E=mc^