dis2-slides

# dis2-slides - ASTR 100 Discussion 2 Sep 19 2011 1 You've...

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ASTR 100 Discussion 2 Sep. 19, 2011

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1. You've seen many stories in the media about the prediction of doomsday in 2012. According to Wikipedia, ONE of the signals of this doomsday is that the Sun will appear to be in a specific position in the constellation of Sagittarius in December 2012. The figure below shows the position of the Earth on its orbit around the Sun on today's date (Feb. 23, 2011). The daily rotation of the Earth on its own axis and the annual orbit of the Earth around the Sun are both indicated. Use this figure to help you answer the question, “Will the Sun appear to be in the constell- ation Sagittarius in December 2012?” STATE YOUR ANSWER AS YES/NO and then carefully explain the steps in your reasoning.

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Answer: The following is an excellent answer by a student: YES. [December is about] 10 months from today. The Earth moves around the Sun over the course of one year and thus moves 1/12 of the way around the Sun every month. As a result, which constellation is highest in the sky at midnight changes every month. According to the orbit shown, on [December] 2012, Gemini will be highest at midnight, and the constell- ation opposite Gemini, Sagittarius, will be highest at noon. During that month, the Sun will appear to be in Sagittarius.
Grading checklist: Did you state yes/no to the question? Did you discuss how the Earth moves in its orbit throughout the year? Did you explain how you know where the Earth will be on its orbit in December 2012?

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2. The diagram below shows the Moon for 5 different phases (A – E). The Moon is either shown as how it would appear in the sky seen from College Park, or in its orbit around the Earth. (Note that for the orbital views, the distances and sizes are not to scale. We are looking “down” on the north pole of the Earth, so
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dis2-slides - ASTR 100 Discussion 2 Sep 19 2011 1 You've...

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