ast$2010:$descriptive$astronomy$...

AST 2010, Exam 2, Winter 2014 Prof. Bonvicini

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AST 2010: Descriptive Astronomy EXAM 2

March 3, 2014

DO NOT open the exam until instructed to. Please read through the instructions below and fill out your details on the Scantron form.

Instructions

1. The exam consists of 50 multiple choice questions.

2. There will be 1 hour and 45 minutes to complete the exam.

3. Answers are to be marked on the Scantron answer sheet provided.

4. A list of useful equations and constants are provided. No student notes are allowed.

5. Please answer using a No. 2 pencil only (pen will not be read by the machine).

6. Read the instructions on the answer sheet for how to mark your answers correctly.

7. Scientific calculators are allowed, however, cell phones are not.

8. Use of cell phones will be considered cheating and will result in a 0.

9. Cheating of any sort is not tolerated and will result in a 0 and potential further

action.

Please now fill in your Last Name, First Name and student ID number in the relevant boxes on the Scantron form. There is no need to fill in the Birth date, Sex or Grade/Education.


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Physical Constants

Name Symbol Value Speed of light c 3 × 108 m s-‐1 Gravitational constant G 6.67 × 10-‐11 m3 kg-‐1 s-‐2 Planck’s constant h 6.63 × 10-‐34 J s Stefan-‐Boltzmann constant σ 6.67 ×10-‐8 W m-‐2 K-‐4 Wien’s law constant T × λmax 2.90 × 106 K nm

Astronomical Constants

Name Symbol Value Astronomical Unit AU 1.50 × 1011 m Light-‐year ly 9.46 × 1015 m = 63,240 AU Parsec pc 3.09 × 1016 m = 206,265 AU = 3.26 ly Year (synodic) yr 365.2422 days = 3.1557 × 107 s Mass of Earth M⊕ 5.97 × 1024 kg Mass of Sun M

! 1.99 × 1030 kg

Equatorial radius of Earth

R⊕ 6378 km

Radius of Sun R! 6.96 × 108 m

Luminosity of Sun L! 3.83 × 1026 W

Hubble’s constant H0 72 km s-‐1 Mpc-‐1

Some useful equations

Geometry

Circumference of a circle = 2πR

Area of a circle = πR2

Surface area of a sphere = 4πR2

Volume of sphere = !! πR3

Distance Relationships

Distance – velocity – time: d = v × t

Linear size -‐ angular size: l = d × α/57.3° Distance from parallax: d (in parsecs) = 1/p(in arcsec)

Hubble’s law (for distance galaxies): d = v/H0


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Gravity

Kepler’s 3rd Law: P2 = a3 when P is in years and a is in AU

Gravitational force between two masses: 𝐹! =! ! !!!

Gravitational potential energy: 𝐸! = − ! ! !!

Newton’s modified form of Kepler’s 3rd law: 𝑀! + 𝑀! = !!

!! (for d in AU and P in years)

Mass of object for orbital speed v and at distance R: 𝑀 = ! !!

!

Escape velocity: 𝑣!"# = !!"!

Light

Frequency (ν) – wavelength (λ) relation: λ × ν = c

Energy of a photon: 𝐸 = ℎ × 𝜈 = ! × !!

Stefan-‐Boltzmann law: L = σT4 × (surface area)

Wien’s Law: 𝑇 = !.!×!!! ! !"

!!"#

Brightness (B) – Luminosity (L) relation: 𝐵 = !!!!!

Doppler effect: Radial velocity = VR = 𝑐 × !"!

Other Physical Relationships

Density = Mass / Volume

Newton’s 2nd Law: F = m × a

Kinetic Energy: KE = ½ m × v2

Conservation of angular momentum: Mass × Circular velocity × Radius = constant


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Questions

1. The ability of a telescope to detect fine detail is called a. Finesse b. Persistence c. Focus d. Aperture e. Resolution

2. The aperture of a telescope if determined by the area of its primary mirror or lens a. True b. False

3. The device used to detect light in digital cameras is called a. Electron modulator b. Photomultiplier tube c. False color image d. CCD (or charge-‐coupled device) e. Aperture

4. The largest telescopes are the optical telescopes a. True b. False


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5. When looking through a green ____________, you see only the green light coming from each object.

a. Aperture b. Coherent c. Filter d. Collecting area e. None of the above

6. If the radius of a telescope’s mirror is doubled, the surface area increases by a. 2 times b. 3 times c. 4 times d. 8 times e. None of the above

7. The diagram below displays an example of a a. Refracting telescope b. Newtonian telescope c. Cassegrain telescope d. Copernican telescope e. None of the above


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8. A refractor and a reflector have the same diameter aperture. A disadvantage of the reflector is that

a. reflectors allow in less light because it is blocked by the secondary mirror

b. reflectors have less magnification c. reflectors do not direct all light to the same place d. None of the above

9. How does the speed of light in glass compare to in space? a. Faster in glass b. Faster in space c. Same in both

10. The bending of light around corners or edges is called: a. Resolution b. Refraction c. Interference d. Interferometer e. Diffraction

11. The angular resolution of a telescope is determined by the _______________ of the telescope and the _____________ of the radiation being observed.

a. Length, wavelength b. Length, color c. Size of the aperture, brightness d. Size of the aperture, wavelength e. None of the above

12. The wavelength regions where the atmosphere does not absorb radiation are called


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a. Adaptive optics b. Atmospheric windows c. Light pollution d. Scintillation e. Seeing

13. ________________ is a measure of the steadiness of the atmosphere during astronomical observations.

a. Adaptive optics b. Atmospheric windows c. Light pollution d. Scintillation e. Seeing

14. The Sun’s visible surface is called the a. Solar corona b. Solar Wind c. Sunspots d. Chromosphere e. Photosphere

15. The process of converting hydrogen into helium in the Sun is called what? a. Radioactive decay b. Neutrino production c. Nuclear fusion d. Nuclear fission e. None of the above

16. On average, the time between solar activity maxima is a. 1 year b. 11 years c. 22 years d. 33 years


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e. 111 years

17. Colder visible regions of the Sun are called a. Aurora b. Coronal mass ejections c. Flares d. Sunspots e. Prominences

18. On the Sun, the equator rotates faster than the area around the poles a. True b. False

19. A parallax angle of 1 arcsecond means that an object is at a distance of ___________ . a. 1 A.U. b. 1 light-‐year c. 1 parsec d. 1 kiloparsec e. None of the above

20. The method of triangulation is good for measuring distances a. Within the solar system b. To nearby stars c. Within our galaxy d. To nearby galaxies e. None of the above


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21. The amount of light reaching us from a star is called luminosity a. True b. False

22. Star A is 10 times brighter than star B, but they have the same luminosity. Which star is closer?

a. Star A b. Star B c. Neither, they are at the same distance

23. Cold stars show absorption lines from heavy elements such as Calcium and Titanium oxide in their spectra.

a. True b. False

24. Differences in spectral type mainly reflect differences in a. Temperature b. Composition c. Neither

25. As two stars orbit each other in a binary system their spectral lines get shifted due to eclipses

a. True b. False

26. The Stefan-‐Boltzmann Law gives the ____________ as a function of temperature a. Total power radiated b. Power radiated per unit area c. Power radiated per unit wavelength d. Flux received on Earth


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e. The wavelength where the emission peaks

27. Suppose there are two stars A and B with the same luminosity. If star A is larger than star B, we can conclude

a. Star A is more massive b. Star B is more massive c. The temperature of star B is lower d. The temperature of star A is lower e. Not enough information to conclude anything

28. In an eclipsing binary star system, the maximum brightness occurs when a. The hotter star passes in front of the cooler star b. The colder star passes in front of the hotter star c. Both stars are visible d. The brightness of the system is constant e. None of the above

29. Below is an H-‐R diagram. Stars in area #1 correspond to a. Main sequence stars b. Brown dwarfs c. Red giants d. Black holes e. White dwarfs


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30. In the above H-‐R diagram, stars in area #2 correspond to a. Main sequence stars b. Brown dwarfs c. Red giants d. Black holes e. White dwarfs

31. In the above H-‐R diagram, stars in area #3 correspond to a. Main sequence stars b. Brown dwarfs c. Red giants d. Black holes e. White dwarfs

32. The _________ the mass of a star, the longer the time it spends in each stage of its evolution.

a. Higher b. Lower c. Doesn’t Matter


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33. The Sun is classified as a high-‐mass star. a. True b. False

34. Which of the following do not have enough mass to fuse hydrogen into helium? a. Main sequence stars b. Red giants c. Super giants d. White dwarfs e. Brown dwarfs

35. Which of the following statements about molecular clouds is false? a. The contain hydrogen b. They contain particles coated in ice c. They contain helium d. They contain iron e. The entire cloud contracts as a whole leading to a gigantic protostar

36. Stars spend most of their life on the main sequence a. True b. False

37. When the core of a star contracts it ___________________ . a. Heats up b. Cools down c. Its temperature stays the same


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38. When entering the giant phase, high mass stars don’t increase in luminosity as much as low mass stars

a. True b. False

39. When a star expands, the surface a. Turns red, heats up and power per square meter is increased b. Turns red, heats up and power per square meter is reduced c. Turns red, cools down and power per square meter is increased d. Turns red, cools down and power per square meter is reduced e. None of the above

40. Variable stars that have no repeated pattern on a light curve are referred to as a. Irregular variables b. Cepheid variables c. RR Lyrae variables d. Mira variables e. Novae

41. The area on the H-‐R diagram where most variable stars are found is called the a. Main sequence b. Supergiant region c. Giant region d. White dwarf region e. Instability strip

42. The period-‐luminosity relation states that longer periods of a Cepheid variable imply higher luminosities

a. True b. False


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43. From the figure below, where on the evolution time line does the star eject its outer layers?

a. 1 b. 2 c. 3 d. 4 e. 5

44. At the center of a low-‐mass planetary nebula is found a a. Planet b. Black Hole c. Neutron Star d. White Dwarf e. Variable star

45. What best describes the evolution of a sun-‐like star from youngest to oldest? a. Black dwarf, white dwarf, red giant, main sequence, protostar b. Red giant, main sequence, white dwarf, black dwarf, protostar c. Protostar, main sequence, red giant, white dwarf, black dwarf d. Protostar, main sequence, red giant, black dwarf, white dwarf e. Protostar, red giant, main sequence, white dwarf, black dwarf


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46. Material from a companion star that accretes onto a white dwarf can trigger a chain reaction of fusion called

a. Thermonuclear runaway b. Coronal ejection c. Electron degeneracy d. Mass transfer e. Recurrent nova

47. When the mass of a white dwarf becomes less than the Chandrasekhar limit, it will collapse.

a. True b. False

48. In a high mass star _____________ cannot be used as fuel a. Oxygen b. Carbon c. Nitrogen d. Silicon e. Iron

49. In the late stages of a high-‐mass red giant, elements are in layers with ________ in the core and _________ in the outermost layer.

a. Hydrogen, Helium b. Helium, Hydrogen c. Helium, Silicon d. Iron, Hydrogen e. Hydrogen, Iron


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50. The sun will become a supernova a. True b. False

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