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Which has a higher intensity viewed from 1 m away? A household 100 W light bulb A 100 W fluorescent overhead tube They will have the same intensity.

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Presentation on theme: "Which has a higher intensity viewed from 1 m away? A household 100 W light bulb A 100 W fluorescent overhead tube They will have the same intensity."— Presentation transcript:

1 Which has a higher intensity viewed from 1 m away? A household 100 W light bulb A 100 W fluorescent overhead tube They will have the same intensity

2 Star G has an apparent magnitude of +5.0 and an absolute magnitude of Star H has an apparent magnitude of +4.0 and an absolute magnitude of Which star appears brighter in the night sky? Star G Star H They will appear the same

3 Altair’s apparent magnitude is and its absolute magnitude is How far is Altair from Earth? Less than 10 parsecs 10 parsecs More than 10 parsecs

4 Which of the following is correct? Apparent magnitude is a measure of intensity Absolute magnitude is a measure of flux Apparent magnitude is a measure of luminosity Absolute magnitude is a measure of luminosity

5 This graph shows the blackbody spectra of three stars. Which has the highest surface temperature? Antares Spica The Sun

6 The surface of Rigel is four times as hot as Betelgeuse, and its diameter is 16 times smaller than Betelgeuse. Rigel is a bit further away from us than Betelgeuse. Rigel is 16 times less luminous than Betelgeuse Rigel is 16 times more luminous than Betelgeuse The stars have the same luminosity You need their exact distances to determine their relative luminosities

7 The star Aldebaran is 10 times closer than Betelgeuse and has roughly the same surface temperature. Using this picture which shows their intrinsic sizes, which of the following is approximately true? We receive 9 times more flux from Aldebaran We receive 9 times less flux from Aldebaran The stars have about the same flux 1200 R sun 40 R sun

8 Alpha Centauri has about the same radius and surface temperature as our Sun, and is about 1.33 pc from Earth. It has apparent magnitude zero, while our sun has apparent magnitude -27. The luminosity of α Cen is larger than our Sun The luminosity of α Cen is much less than our Sun The flux from α Cen is about times less than our Sun The absolute magnitude of α Cen is much smaller than our Sun

9 A thin, cold gas cloud lies between you and a bright blackbody. Which of these spectra would you expect to see when you look toward the blackbody? Spectrum A Spectrum B Spectrum C None of these

10 Astronomers determine the “color” of a star by calculating the ratio of fluxes as measured with two different filters difference between the fluxes as measured with two different filters ratio of the absolute and the apparent brightness difference of the absolute and the apparent brightness Does Betelgeuse look reddish to you? Go outside tonight and see!

11 The main reason that flux measurements with filters gives temperatures of stars is Hotter stars lie further away from us More luminous stars lie further away from us If you compare any two stars, the colder one is always less luminous The light from colder stars always peaks at lower frequency

12 Two stars are in a binary system and are separated by 200 A.U. Star 1 is 5 solar masses. Star 2 is 2 solar masses. The period of star 1 around the center of mass is ______ the period for star 2 around the center of mass. larger than smaller than the same as not enough info given to answer this

13 The spectrum of Sirius A peaks at 5.8 x Hz. The spectrum of Sirius B peaks at 1.5 x Hz. From this information alone, you can deduce that Sirius A is smaller than Sirius B Sirius A is less luminous than Sirius B Both of the above are true You can’t deduce any of the above

14 In a binary star system, star A is twice as massive as star B. The orbital plane is at an inclination of 45°. Which of the following is always true? Star A will experience larger blue shifts than B Star A will experience smaller blue shifts than B The orbital period of star A is larger than star B The orbital period of star A is smaller than star B

15 For stars larger than the Sun, luminosity goes as (mass) 4, while radius goes as (mass) 0.5. If every star uses up the same fraction of its mass over its lifetime, then you would expect that: High mass stars live longer Low mass stars live longer High and low mass stars live to about the same age More luminous stars live longer

16 In space you come across some neutral 3 H. Your ship’s sensors tell you that it has 1 neutron, 1 proton and 1 electron 1 neutron, 1 proton, and 2 electrons 1 neutron, 2 protons, and 2 electrons 2 neutrons, 1 proton, and 1 electron

17 An interstellar cloud is made up of a neutral gas that is 25% Hydrogen by mass and 75% Helium by mass. Its mean molecular mass is: 13/4 7/16 16/7 4/13

18 If you fully ionize an initially pure Helium gas, its mean molecular mass will: Decrease by a factor of 3 Increase by a factor of 3 Increase by a factor of 4 Decrease by a factor of 4

19 Our Sun doesn’t collapse under its own gravity because: Its atoms are packed extremely tightly together Its hot gas exerts pressure Its atoms electromagnetically repel each other It produces huge numbers of photons in its core

20 Given what you know about surface gravity and mass-radius relations for main sequence stars at least 1.66 times as massive as our Sun: The surface gravity varies very little with mass More massive stars have much higher surface gravity Less massive stars have much higher surface gravity

21 Which class of main sequence star has the longest lifetime? Class A Class M Class O These all have about the same lifetime

22 The luminosity classes of main sequence stars: depend on both radius and temperature depend solely on mass depend solely on luminosity are all about the same as our Sun’s

23 Using the spectroscopic parallax method, you measure a star to be 76 pc away. You now find out that the star is actually luminosity class I instead of class V. That makes your original distance measurement Too large Too small Correct – no change to your estimate is needed

24 The spectral class of a star depends solely on temperature mass luminosity radius

25 (Optical) Deep Thoughts: If the Sun is a giant ball of gas whose pressure drops off as -dP/dr, and photons are produced only in a small region in its center, then why does it look like a circular disk?

26 Which of the following has an optical depth much smaller than 1? Your textbook in visible light Our atmosphere in gamma-rays The walls of this classroom in radio waves A mirror in visible light

27 If there is such a steep temperature gradient inside the Sun, then why does its spectrum look like a blackbody?

28 The mean free path can be described as: Inversely proportional to opacity and density The average distance travelled by a particle between collisions The distance over which the optical depth grows from zero to one All of the above

29 You might expect the mean free path of a photon that starts out deep inside the Sun to be Much longer than a solar radius Much smaller than a solar radius About equal to a solar radius About equal to one astronomical unit

30 If you were to suddenly crank up the energy generation rate at the center of the Sun, the inner regions of the Sun would Be more likely to transfer heat via convection Remain unchanged Be more likely to transfer heat via radiation Be more likely to transfer heat via conduction

31 make the layer less likely to be convective flatten the temperature gradient steepen the temperature gradient have no other effect on the layer

32 Consider the following mass comparisons (in atomic mass units): Proton mass = 1 Hydrogen atom mass = Neutron mass = Helium atom mass = Why does helium (2 protons + 2 neutrons) have a mass less than 4? Some helium atoms have less than 2 protons The mass is lost when two protons are converted to two neutrons It takes energy to pull a helium nucleus apart Helium atoms move so fast that they have a lower apparent mass

33 In general, fusion is most likely to occur between two particles with High relative velocity High electric charge with the same sign High masses High magnetic charge

34 The Sun’s corona has temperatures roughly as hot as the Sun’s core. So why doesn’t fusion occur in the corona? The gas density is too low The gas is fully ionized The gas is only 70% hydrogen All of the above

35 About 25% of the mass of a newborn star is helium. Why doesn’t it fuse while the star is on the main sequence? Helium fusion requires three nuclei to interact within a very short amount of time For a given gas temperature, helium nuclei move slower than hydrogen nuclei Helium nuclei repel each other more strongly than hydrogen nuclei All of the above

36 The energy from fusion reactions that goes into neutrinos doesn’t heat up the Sun because neutrinos are massless and thus carry no energy have no electric charge have a very large mean free path rapidly decay

37 A star remains at constant size and temperature for a long period of time. Which of the following is mostly likely to be true? The star generates about as much energy as it radiates more energy than it radiates into space less energy than it radiates into space

38 When starlight passes through interstellar dust The wavelengths all get longer (redder) It gets fainter The red light tends to scatter sideways while the blue continues to us All of the above

39 An interstellar dust cloud drifts in front of a star. In terms of numerical values for color index and apparent magnitude, its observed (B – V) is larger, and m V is smaller (B – V) is larger, and m V is larger (B – V) is smaller, and m V is smaller (B – V) is smaller, and m V is larger

40 In terms of mass, the largest component of the interstellar medium is Helium gas Dust Hydrogen gas Planets

41 Hot emission nebulae are somewhat red, and cool reflection nebulae are blue. Why are these colors different from what Wien's law tells us about the radiation emitted by a blackbody? The regions producing light in emission nebulae are optically thick The dust grains in reflection nebulae scatter longer wavelengths of visible light better than shorter wavelengths. The light we see from emission nebulae has been strongly absorbed by dust None of the above

42 Which of these would have the largest diameter H II region? O3 V star surrounded by a hydrogen cloud with a low free electron density G2 V star surrounded a hydrogen cloud with a low free electron density G2 V star surrounded a hydrogen cloud with a high free electron density O3 V star surrounded by a hydrogen cloud with a high free electron density

43 If a free electron encounters a magnetic field it will Accelerate away from it and emit nothing Ignore it Accelerate toward it and emit radiation Annihilate and produce a gamma-ray

44 As you increase the eccentricity of an orbit, it becomes more elliptical, and the focus Moves towards the center of the ellipse Stays put Moves towards the edge of the ellipse Moves to a point outside the ellipse

45 If you perturb the edge of a molecular cloud, the perturbation will travel through the cloud on the free-fall timescale at the speed of light at the speed of sound on the thermal timescale

46 If the material in the primordial Solar System retained its angular momentum as it collapsed to form the Sun, the Sun’s current rotation rate should be Slow (more than a month period) Fast (less than a week period) Moderate (week to a month period) Zero (non-rotating)

47 According to the Virial theorem, if you compress a ball of gas in hydrostatic equilibrium: The temperature of the gas will remain the same The temperature of the gas will increase The temperature of the gas will decrease

48 For our Sun, which is longest – the thermal timescale (GM 2 /LR), the free-fall timescale (R 3 /GM), or the nuclear timescale (2 Myr x M/L) ? note: 1 year ≈ π x 10 7 sec. nuclear thermal free-fall all three are roughly the same

49 If the charge on the proton were increased, then the masses of the lowest mass stars on the main sequence would be unchanged smaller larger

50 The main source of pressure in a degenerate gas is The low number density of the particles The high kinetic energies of the particles The filling up of available energy states Degenerate gasses do not supply pressure

51 In a fully degenerate gas, the pressure is dependent on: The density and temperature The temperature only The density only

52 Which is the oldest open cluster here? NGC 188 NGC 2362 h + χ Persei All are about the same age

53 Our Sun doesn’t pulsate because Its oscillations aren’t driven at the right period There is no companion star to perturb it It is no longer on the main sequence Its outermost layer is convective

54 White dwarfs support themselves against gravitational collapse by Coulomb pressure Helium gas pressure Carbon gas pressure Electron degeneracy pressure

55 Which is ranked correctly from least dense to most dense? Black hole, white dwarf, neutron star Neutron star, black hole, white dwarf White dwarf, neutron star, black hole All of three have about the same density

56 If were to drop your pen from 1 m high on the surface of a 1 solar mass neutron star, it will hit the surface at 10 4 m/s 10 m/s 100 m/s 10 6 m/s

57 Our Sun will end up as A white dwarf A black hole A neutron star A supernova remnant

58 The mechanism that makes a white dwarf shine is Fusion of material dumped on its surface Gravitational contraction Nuclear fusion in the core region Escape of heat left over from its formation

59 In order for a white dwarf to become a nova it must Have had a main sequence mass > 7 M sun Be heavier than 1.44 solar masses Have a companion star Continue fusing elements up to iron

60 It is much more difficult to escape the surface of a neutron star compared to a normal star because It is much hotter It is much heavier It is much denser It has much lower surface radiation pressure

61 If a pulsar rotates 1000 times per second, special relativity and classical mechanics imply that compared to a normal star it must be Much larger and less dense Much larger and denser Much smaller and denser Much smaller and less dense

62 A supernova is Something our Sun will eventually do The eventual fate of a very high mass star A really bright nova event The creation of a very high mass star

63 The event horizon of a 1.0 M sun black hole is 3 km. Thus, the event horizon for a 2 solar mass black hole must be 3.0 km 0.75 km 1.5 km 6 km

64 If our Sun were to suddenly replaced by a 1 M sun black hole, the Earth would Start to fly outward at a tangent to its orbit Start to spiral inward toward the black hole Stay in its current orbit Start to fly outward in a direction opposite to the black hole

65 An astronaut falling into a black hole would be ‘spaghettified’ by Magnetic forces: the black hole’s powerful magnetic field pulls her apart Tidal forces: gravity pulls her feet much stronger than her head Centripetal forces: the rapid rotation of the event horizon stretches her out

66 Black holes are black because They are extremely cold They are blackbodies Their escape velocity exceeds light speed They are theoretical objects that have never been seen

67 In a supernova or gamma-ray burst, what type of energy is converted to radiation? Electromagnetic Thermonuclear fusion Neutron degeneracy Gravitational

68 If a W gamma-ray burst exploded at the distance of Alpha Centauri (1 pc), it would appear: (hint: 1 pc roughly 200,000 AU) Considerably fainter than the Sun Considerably brighter than the Sun About the same brightness as the Sun

69 The radius of a star’s orbit and its velocity – the data implied by a star’s location on a rotation curve – can be used to determine The mass interior to the star’s orbit The mass of the star The mass of the entire galaxy The mass at the center of the galaxy

70 Which curve represents the trend of velocity versus radius for a solid rotating disk? Red Blue Green None of these

71 Young stars are predominantly found in the ___ of our galaxy since _____ there causes stars to form. Disk, a density wave Disk, low metallicity gas Halo, high density gas Bulge, supernovae

72 (A) (B) (C) (D)

73 Edwin Hubble’s ‘tuning fork’ diagram describes How astronomers classify galaxies Different possible models for our Milky Way How galaxies evolve, from left to right How Ed Hubble liked his lattes prepared

74 Optical telescopes can’t give us a good view of the galactic center because Optical telescopes currently aren’t large enough There is too much dust in the way The galactic center is too far away Our atmosphere distorts the images too much

75 Which observation would provide the best evidence that the disk of the Milky Way does NOT rotate like a solid wheel? Disk stars twice as far from the galactic center rotate twice as fast around it Disk stars have Doppler shifts The brightest disk stars form spiral arms The rotation of the disk stars near the Sun decreases with distance according to Kepler’s laws

76 The currently accepted value for the Hubble constant is about 70 km/s/Mpc. If we were to suddenly discover it was actually 200 km/s/Mpc, the age of the universe would then be About the same age as we previously thought Much older than we previously thought Much younger than we previously thought

77 Consider three widely separated galaxies in an expanding universe. Imagine you are located in galaxy A and have observed that both galaxies B and C are moving away from you. What would someone in galaxy C say about the motion of B? It is moving away from them It is not moving It is moving toward them A BC

78 Say you want to measure the distance to the closest galaxy (Andromeda). The best method to use is Doppler shift of its spectral lines Period-luminosity relation for Cepheid stars The Hubble law of recession for galaxies Trigonometric parallax using Earth’s orbit

79 In the radio galaxy M87, you can only see one jet because Light from the other jet is beamed away from us Dust is obscuring the other jet Only one jet is currently being produced The other jet is so far away its light hasn’t reached us yet

80 The large Doppler velocity widths of broad emission lines in active galaxies could NOT be created by hot emitting clouds that are Being ejected along a narrow-angled jet Swirling at high velocities around a black hole Falling into the neighborhood of a black hole

81 The most distant quasar at z = 7.1 has an apparent optical magnitude of 21. How much fainter is it than the faintest star you can detect with your naked eye (magnitude = 6) ? 100 x 1000 x 1,000,000 x 1,000,000,000 x

82 You detect a narrow width Lyman α absorption line in the spectrum of a quasar which is at a significantly shorter wavelength than the quasar’s observed Lyman α emission line. You conclude that the absorbing cloud is Warm and located close to the quasar Cold and located close to the quasar Cold and located close to the Milky Way Warm and located close to the Milky Way

83 At high redshift, a larger fraction of galaxies are “active” than at low redshift. From this, we can safely conclude that All galaxies may become active more than once in their lifetime All galaxies go through an active phase, and fewer galaxies in the past were active than now Some galaxies go through an active phase, and more galaxies in the past were active than now Most galaxies never become active in their lifetime

84 Which cluster is the most likely to be relaxed? Cluster B Cluster A

85 Gravitational lenses are often detected at optical wavelengths because Dark matter absorbs light at all other wavelengths Gravity bends spacetime only for optical wavelengths There is typically less obscuration in the optical Distant background galaxies emit most of their light in the optical

86 When Andromeda and our Milky Way merge, Very few of the stars in either galaxy will survive The dark matter halos will annihilate each other in a giant explosion A new elliptical galaxy will eventually form The two galaxies will annihilate each other, since Andromeda is made of antimatter

87 Which of the following measurements can NOT be used to measure the amount of dark matter in a galaxy cluster? The deflection of light rays from a background object passing by the outskirts of the cluster The average speed of galaxies orbiting the cluster center The dispersion in the speeds of the galaxies orbiting the cluster center The properties of X-rays emitted by gas that has been heated by falling into the cluster

88 The night sky is relatively dark because the Universe is very large is filled with light-absorbing dust is mostly empty has a finite age

89 Olber’s Paradox asks why the night sky is dark, when every line of sight must eventually fall on a star. It is dark primarily because the Universe is Expanding, so that distant stars are redshifted Infinite and mostly empty Young, so there are only stars out to a finite distance Clumpy, so that not every sightline hits a star

90 The near-perfect blackbody spectrum of the cosmic microwave background implies that at one time, the Universe was very much like a giant black hole the Universe was optically thick the mean free path of photons in the Universe was very long the Universe was much colder than it is now

91 The cosmic background radiation is visible in every direction since We are looking back to when the Universe was cold We are at the center of the Universe We are looking back to when the Universe was young in every direction It has scattered in every direction over the age of the Universe

92 Dark matter has so far not been detected in the lab most likely because Radiation pressure from our Sun pushes it outward Dark matter is only found in distant galaxies It rarely interacts with normal matter It has a very short decay half life

93 The observed redshifts of galaxies mean that Photons lose energy as they travel through space We are the center of an expanding Universe Gravity can never overcome the expansion left over from the Big Bang Galaxies were moving much faster with respect to each other when the Universe was very young

94 The consensus model of cosmology indicates The expansion of the Universe has stopped The expansion of the Universe is slowing The expansion of the Universe is accelerating The Universe is currently contracting

95 The lookback time to an object is the # of years between when the object emitted its light and when we see it. What piece of information surely does NOT affect the lookback time for a distant object? The rate of expansion of the Universe Its distance The speed of light The wavelength of light being observed

96 As the Universe evolves over time The energy density of dark energy remains constant The energy density of dark matter increases The energy density of dark energy increases The energy density of dark matter remains constant

97 Since the time when the cosmic microwave background was created, the Universe has expanded by approximately a factor of million

98 The luminosity distance is defined as the distance over which The universe has expanded in the time the light from the object takes to reach us The small angle formula applies The comoving coordinates stay constant The inverse square law of light applies

99 By observing the cosmic microwave background, the Planck mission confirmed that on the whole, spacetime in the Universe is Positively curved, like a sphere Negatively curved, like a saddle Flat

100 Which product name isn’t associated with an astronomical phenomenon? Starburst Pulsar Nova Quark

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