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Flashcards in Final Exam Deck (40)
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41- a) What is an exit cone for light, and why does it exist? Use diagram(s) and a few sentences. Show what happens to light shining within the exit cone, and outside it.

a) The lowest escape velocity from any object is straight up, otherwise the curvature of spacetime requires greater and greater velocity as the object has to overcome the curvature. For huge objects, sometimes the escape velocity gets so high that nothing can escape it- not even light. An exit cone are the possible paths that light can take to escape (the more direct/less curvature regions.)

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41b) What happens to the exit cone at an event horizon?

b) At an event horizon, the exit cone for light disappears. This is because the curvature of space at event horizon is so great that not even light can escape it.

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43- a) What do astronomers look for to detect a stellar black hole, and why?

a) Astronomers look for a binary system with a red giant and a dark companion. They hope that the large volume of the red giant would push it beyond the Lagrangian point of the system, so that material from it enters the black hole’s accretion disk. This material is then heated up and emits tons of xrays.

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43b) What was the name of the first one discovered, in what decade was it discovered?

b) Cygnus X1- 1964! Notes say 74...

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45- a) Describe the density wave theory of galactic spiral structure. How do the arms maintain themselves in this theory, and how does it change our thinking about galactic rotation rates?

a

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45b) How does this theory help explain the birth of stars?

A

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46- a) Draw a graph of the Hubble law.

A

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46b) How did astronomers gather the information needed to establish the law?

A

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46c) What is the definition of the Hubble constant, and what is its value thought to be today?

A

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47- a) How and when was the first quasar discovered? Include its name and a graph and diagram illustrating the method.

A

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47b) Why are quasars hard to explain?

A

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48- a) Describe how our universe could be finite in spatial size but not bounded in any direction.

A

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48b) Also use a diagram and a few sentences or equations to derive an expression for the approximate age of the universe from the Hubble constant. Assuming gravity has always been the ruling force over long distances, is that estimate an upper or lower limit, and explain why?

A

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49- a) Draw the Friedmann and Steady State models of the universe on a graph of scale parameter vs. time. Indicate where the present time is on the graph.

A

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50- Why does the cosmic background radiation (CBR) favor the Friedmann model over the steady state model? Explain how the CBR originated and when, using a graph and a few sentences.

A

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51-a) What is the evidence for dark matter? Include as much as you can, and use diagrams where appropriate to explain it.

A

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53- a) Name 4 problems with cosmology as it existed about 25 years ago, and briefly describe each one.

A

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1- a) List 3 physical properties that are vector quantities, and 3 that are not.

a) vectors: acceleration, pressure, velocity
not vectors: energy, time, mass

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1b) Write a few words or a sentence that describes conceptually what each one means.

b)
velocity: change in the position of an object over time
acceleration: change in the velocity of an object over time
pressure: force (push or pull) applied to a unit of area
mass: resistance to acceleration.
time: an amount of time, another dimension of space
energy: potential to do work.

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5- a) Why are radio telescopes sometimes linked together to form an "interferometer"? In other words, state what problem this helps to solve.

a) Interferometry is combining more than one radio telescope to gather data. Combining data from more than one telescope effectively creates one telescope as large as the distance between the telescopes involved. This allows for much greater resolution and smaller beam width when studying the sky.

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5b) Discuss why "adaptive optics" are used in modern optical telescopes, and basically how that technology works.

b) Adaptive optics is when a reflecting mirror is made of many small individual mirrors that can be adjusted. They are adjusted to counter atmospheric turbulence and thus gain a much sharper image.

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7- a) Name and briefly describe two effects that prove that the Earth rotates on its axis.

a) 1. coriolis effect: Geometry of the rotation of earth deflects massive objects to appear to turn clockwise in northern hemisphere and counterclockwise in southern hemisphere.
2. foucault pendulum: As the earth spins on its axis, a pendulum not restricted to one plane will precess and change its plane

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7b) Illustrate one of these effects with a diagram.

b) Draw coriolis, twirl on atmosphere going LOOK UP DIRS

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9- a) In a few words, name 2 reasons we have the seasons on Earth?

a) Because of the Earth’s 23.5° tilt, the sun’s light hits the northern and southern hemispheres of the Earth at different angles at different times of the year (as Earth revolves around the sun).
1. During the winter, a shaft of sunlight hits a wider area of the Earth’s surface than it does in the summer. This means that the same amount of light is spread across a wider area, thus heating that area less than the smaller area it would hit in summer.
2. The hemisphere in winter spends less time on the day side of the terminator. This means the day is shorter, meaning that it is exposed to sunlight for shorter periods of time. Less time being heated means lower temperature.

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9b) Include an Earth diagram, showing the Tropics, Arctic and Antarctic circles with their latitudes, plus incoming sunlight and the terminator for late June.

b) Tropic of cancer is 23.5°N, Capricorn is 23.5°S, artic circles are 66.5(CHECK)°, incoming sunlight+terminator for late june has terminator bending L->R.

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14- a) Use 2 diagrams of sun, earth and moon to show: 1- the three types of lunar eclipses; 2- the three types of solar eclipses. Label each type of eclipse, and describe its appearance.

a) Refer to notes to plan out diagram. Definitions;
Lunar Eclipses
Total LE: When the moon is caught completely within the umbra (shadow) of the Earth, moon is much darker and has a reddish appearance
Partial LE: When the moon is between the umbra and penumbra of the Earth. - part of the moon looks dark and red, the rest is normal.
Penumbral lunar eclipse: When the moon is in the penumbra of the Earth. Moon looks no different, has to be measured to pick up difference.

Solar eclipses:
Total solar eclipse: The moon completely blocks the sun (earth is in the umbra), only the sun’s corona is visible.
Partial solar eclipse: The moon partially blocks the sun, earth is in both the umbra and penumbra of the moon, giving the sun a crescent shape.
Annular solar eclipse: The moon is at or near aphelion and appears too small to completely obscure the sun. Moon looks like a concentric circle within the sun.

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14b) Draw a diagram showing the forces that cause the tides on Earth.

b) Gravitational force arrows around the planet cause bulging on both sides, direct pull of moon+tidal forces on other side.

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15- a) Describe what it would be like to stand on the dayside of the moon. Include a description of the ground, approximate temperature compared to earth, gravity, appearance of the sky and how you see the earth move in the sky above you.

a) On the dayside of the moon it would would be extremely hot, around 240° fahrenheit. All around you is the bleak, black and white lunar landscape. Your boots are in 2-6” of lunar dust. The sky is night sky except for the earth and maybe the sun. The earth doesn’t move. The gravity there is 1/6th that of earth so you can jump really high

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15b) At midday on the moon, what phases are possible for the Earth as you would see it, and draw a diagram to illustrate this answer?

b) Draw diagram but remember ALWAYS DAYSIDE OF MOON.

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18- a) Describe two substantially different astronomical measurements that are made possible by the Doppler shift of light. Include a diagram for each.

a) 1. One measurement that is made possible by the doppler effect is measuring the radial velocity of something. By calculating the “real” wavelength of the object, and knowing the speed of light and the doppler’d wavelength, we can know if the object is moving to or away from us and at what speed.
2. Another measurement is the rotational speed of a body. Measure the blueshift of the side coming towards you and the redshift of the side moving away to get its rotational velocity.