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# mta - ASTRONOMY 294Z The History of the Universe Professor...

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ASTRONOMY 294Z: The History of the Universe Professor Barbara Ryden MIDTERM EXAM: SOLUTIONS Short-Answer Problems 1) Arrange the following scientists in order of when they lived, earliest to latest: Isaac Newton, Aristarchus, Nicolaus Copernicus. Aristarchus first, then Copernicus, then Newton. 2) You step outside on a clear night in Ohio. Over the course of the night, do stars appear to circle clockwise or counterclockwise around Polaris? Counterclockwise. 3) Name one of the reasons why the heliocentric model of Copernicus met with initial resistance. Choose one: it was heretical, the rapid motions implied boggled people’s minds, Copernicus was a boring writer, and (perhaps most decisively) stellar parallax was not observed. 4) Which scientist was the first to eliminate the celestial sphere from the heliocentric model: Copernicus, Digges, Kepler, or Newton? Thomas Digges 5) Suppose that mischievous space aliens move the Earth so that it’s on a larger orbit around the Sun. On its new orbit, would the Earth’s orbital period be longer or shorter than it is now? Longer. 6) If the universe were contracting rather than expanding, would we see galax- ies redshifted or blueshifted? Distant galaxies would be coming toward us, so we’d see them blueshifted. 7) At rest, hydrogen absorbs light with a wavelength λ 0 = 656 . 3 nanometers. You observe a star with a hydrogen absorption line at wavelength λ = 656 . 5 nanometers. Is the star moving toward you or away from you? The wave- length is increased by the Doppler effect; therefore the star is moving away from you.

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8) If a star has a parallax angle of 0.1 arcsecond, what is its distance, in parsecs? 10 parsecs. (Distance in parsecs equals one over the parallax angle in arcseconds.) 9) If a star is at a distance of 1 parsec, what is its parallax angle, in arcsec- onds? 1 arcsecond. (This is how the distance of 1 parsec is defined, in fact.) 10) Two stars have the same luminosity, but different distances. Which star will have the larger flux: the nearer star or the farther star?
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mta - ASTRONOMY 294Z The History of the Universe Professor...

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