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Course: AST 294, Fall 2009School: National Taiwan University
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294Z ASTRONOMY The History of the Universe Professor Barbara Ryden Problem Set # 4 Due Tuesday, February 5 at class time NAME (please print clearly): SCORE (instructor use only): Reminder: The midterm exam will be on Thursday, February 7, at class time. 1) [20 points] Today, the average density of matter in the universe is = 3 10-27 kg/m3 . If the matter consisted entirely of hydrogen atoms, how many...
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294Z ASTRONOMY The History of the Universe Professor Barbara Ryden
Problem Set # 4 Due Tuesday, February 5 at class time
NAME (please print clearly):
SCORE (instructor use only):
Reminder: The midterm exam will be on Thursday, February 7, at class time.
1) [20 points] Today, the average density of matter in the universe is = 3 10-27 kg/m3 . If the matter consisted entirely of hydrogen atoms, how many hydrogen atoms (on average) would be contained in a cubic meter of the universe? If the matter consisted entirely of regulation baseballs (of mass M = 0.145 kg apiece), how many baseballs (on average) would be contained in a cubic astronomical unit of the universe?
2) [20 points] The temperature of the cosmic background light today is T 3 K. At the time the universe became transparent, the temperature of the cosmic background light was T 3000 K. This means that the universe has expanded by a factor of 1000 since it became transparent. If the density of matter today is = 3 10-27 kg/m3 , what was the density of matter when the universe became transparent? [Hint: you may assume that matter is neither created nor destroyed.]
3) [20 points] the At time of primordial nucleosynthesis, the temperature of the cosmic background light was T 4.8 108 K. By what factor has the universe expanded since the time of primordial nucleosynthesis? If the density of matter today is = 3 10-27 kg/m3 , what was the density of matter at the time of primordial nucleosynthesis?
4) [20 points] Look up the density of the Earth's air at sea level. (Using an online search engine is probably the simplest way of doing this, but you can also harass a reference librarian or use an old-fashioned dead-tree encyclopedia.) Is the density of matter at the time of primordial nucleosynthesis greater than or less than the density of the Earth's air at sea lev...
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National Taiwan University - AST - 294
ASTRONOMY 294Z The History of the Universe Professor Barbara RydenProblem Set # 3 Due Tuesday, January 29 at class timeNAME (please print clearly):SCORE (instructor use only):1) [20 points] You are given a ticket for running a red traffic lig
National Taiwan University - AST - 294
ASTRONOMY 294Z: The History of the Universe Professor Barbara RydenSOLUTIONS TO PROBLEM SET # 71) [20 points] The age of the universe (that is, the time since the Big Bang) is 14 billion years. The age of the Solar System is 4.56 billion years. Th
National Taiwan University - AST - 294
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National Taiwan University - AST - 143
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National Taiwan University - AST - 825
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National Taiwan University - AST - 825
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National Taiwan University - AST - 825
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National Taiwan University - AST - 825
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