Final Exam Flashcards
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.)
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.
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.
43b) What was the name of the first one discovered, in what decade was it discovered?
b) Cygnus X1- 1964! Notes say 74…
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
45b) How does this theory help explain the birth of stars?
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46- a) Draw a graph of the Hubble law.
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46b) How did astronomers gather the information needed to establish the law?
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46c) What is the definition of the Hubble constant, and what is its value thought to be today?
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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.
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47b) Why are quasars hard to explain?
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48- a) Describe how our universe could be finite in spatial size but not bounded in any direction.
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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?
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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.
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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.
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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.
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53- a) Name 4 problems with cosmology as it existed about 25 years ago, and briefly describe each one.
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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
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.
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.
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.
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
7b) Illustrate one of these effects with a diagram.
b) Draw coriolis, twirl on atmosphere going LOOK UP DIRS
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.
