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NAME       Adam Seering      

Astronomy Quiz #1

Directions: Answer 3 of the first 5 questions and #6

1. Explain why astronomers don't use 24 hour clocks.  Draw a diagram to illustrate why a single earth rotation about its axis takes less that 24 hours.  How does Earth's axial rotation, coupled with its elliptical orbit around the sun account for the Analemma photo you analyzed?  How do you take such a photo?

  The Earth does not rotate 360 degrees in one solar day; it just rotates so that it is facing the sun again.  Because it is also orbiting the sun, this combined motion offsets the Earth's 'day' from a complete rotation.

  For the most part, astronomers spend their time looking at objects other than the sun, so they don't care as much where the sun is.  Because the Earth does not orbit the rest of the universe as it orbits the sun, astronomers use clocks whose complete day is equivalent to an Earth rotation (sidereal time), not an Earth rotation plus the extra part of a rotation needed to face the sun.

  The Earth does not move in a circle around the sun; as a result, the earth appears to move faster or slower relative to the sun depending on its location in its orbit.  As a result, for part of the year, the sun seems to fall behind in its rotation, and for part of the year it catches up.  As it falls behind, it moves farther east at a given time of day; as it catches up, it moves farther west.  Also, as the side of the Earth that faces the sun (relative to its tilted orbital axis) changes, the height of the sun in the sky increases and decreases.  Both of these cycles occur over the course of a year, so they combine to make the figure-8 pattern.  To take the Analemma photograph, one would have to take a composite photograph of the sun's location at a specific time of day once every week (or similar interval), at the same time of day.

2.  a) Briefly describe the method used by Eratosthenes to measure the circumference of the Earth.

  He synchronized two clocks in two different cities, cities that were fairly far away.  He set them so that, in the first city, it was noon when an object sticking straight up had no east-west shadow.  He then measured the shadow of an object sticking straight up in the second city, and that difference in angle was equivalent to the angle from the center of the Earth to those two cities (see diagram).

  Then, the simple math equation (theta / distance between cities) = (360 / Earth's circumference) gives the Earth's circumference (he also measured the distance between the cities ahead of time).

  b) Briefly describe how you can use a pinhole camera to measure both the diameter and angular size of the Sun.

  Using a pinhole camera, you get the following ratios between distances (see diagram):

(d / D) = (h / H) = (s / S)

  These relations are true because you have a set of similar triangles.  d, h, and s are measurable, so if you know either D, H, or S, you can solve for the other two.  Also, Theta can be found by geometrically solving either of the two triangles.

3. Draw diagrams and explain why:

a) We never see Mercury at night.

b) We never see a thin crescent moon at midnight?

c) We get the best views of Saturn when it is at opposition.

4. What does it mean for the sun to be in Virgo? Draw a diagram that illustrates the sun's tour through the zodiac.  Explain why Polaris, the north star, will eventually give up this role, as it will no longer still point north.  What is the ecliptic and how does it ensure that Hercules will never become a sign of the zodiac?

5. Explain how the Anasazi used the Sun to determine the time of year (when to plant crops, when to harvest, etc.) Compare and contrast the achievements of the Anasazi with those of the ancient Babylonians.  What significant element of astronomy was missing from the Babylonians and finally incorporated in the astronomy of ancient Greece?

6. The United States Government withdrew its support of the construction of a "Superconductor Supercollider" in the 1980's.  The collider would have physicists in formulating a grand unified theory, or theory of everything (one that successfully united Relativity and Quantum Mechanics).  Many argued that such a theory would give humans access to "the mind of god".  In the process, some believed, it would also make science no longer necessary (there would be no need to debate science, as all would be known).  In The Elegant Universe, Greene provides a reason for the study of string theory, and suggests that it might be a good candidate for a fundamental grand unified theory.

(i) What is the motivation, according to Greene, to study string theory?

  We should attempt to develop a complete theory to describe everything, not because it would be the end of science, but because it would be a new beginning, letting us study and understand things that completely confused all scientists before the creation of such a theory.

(ii) In your opinion, do you believe seeking out such a theory is inappropriate for humanity and detrimental to science? Did our government proceed in error?

  I think that seeking out such a theory is appropriate, because even having such a theory would not let us understand the entire universe.  There is still too much for us to process for us to ever understand more than a select few areas of interest.  As to if some far superior being, who could understand everything and even, maybe, predict the future, should understand such a theory, that is another question entirely; I would have to meet such a being before judging on the matter.  I think that our government did proceed in error; I believe that no human can ever discover too much information, at least in the world as I understand it now.