Astronomy II (Astr 1020) Homework #7 for Spring 2008 by Prof. Richard Ignace - Prof. Richa, Assignments of Astronomy

Download Astronomy II (Astr 1020) Homework #7 for Spring 2008 by Prof. Richard Ignace - Prof. Richa and more Assignments Astronomy in PDF only on Docsity! Astronomy II (Astr 1020) Spring 2008 Prof Richard Ignace HOMEWORK #7 Notes: You will need a calculator, a pencil, and a standard scantron. Each question has one correct answer. Choose the best answer for each. Mark your answer on the scantron. This homework is due at the beginning of class on April 24. Late homeworks will not be accepted. 1. Consider an Earth-like planet orbiting a Sun-like star. The orbit has the properties of a semi-major axis f a = 1 AU, an orbital period of P = 1 year, and an eccentricity e = 0.6. If the habitable zone stretches from 0.9 to 1.3 AU, might you expect to find life on this planet? a) No, life does not exist on Earth-sized planets. b) No, life does not exist in the habitable zone. c) No, the planet’s orbit is not always inside the habitable zone. d) Yes, the planet’s orbital period is just right for life. e) Yes, the planet’s orbit is always inside the habitable zone. 2. Let’s play a silly game called the Cosmic Postman. Suppose that every star has one planet with an intelligent civilization. They have all being launching info “packages” every year for the age of the Milky Way. Doing the math, this works out to a number density of randomly “floating” packages at about n = 2×10−31 per cubic kilometer. Statistically, the amount of time before one of these packages randomly strikes the Earth is t ≈ 1/(nπR2v), where R = 6400 km for the radius of the Earth, and v = 6.6 × 109 km/year for the speed of the Earth around the Milky Way as it is carried along by the Sun. Estimate the number of years before the Earth hits a package. a) 2 × 1020 years b) 2 × 1016 years c) 5,900 billion years d) 2 × 105 years e) 0.0059 years 3. Which of the following terms of the Drake equation will most likely have a good estimate in the near future? a) The fraction of stars that have planets. b) The fraction of planets that have life. c) The fraction of life-bearing planets with intelligent life. d) The fraction of intelligent life that is communicative. e) The average lifetime of a technical civilization. 1