Astronomy 250Problem Set No.2Due: Jan 31, 2002 5pm

Remember that you may discuss these problems with others in the class but you must turn in your own work. Be careful in writing up your calculations and results as items will be marked as incorrect if illegible. This problem set is worth a total of 25 points with the value of each problem as marked.

Problem 1 (5 points): Two stars are observed. One has its peak output at 550 nm while the other has its peak at 920 nm. What are the temperatures of these two stars? Assuming that they are at the same distance from us, what are their relative total fluxes? Plot the curve of relative flux versus wavelength for the cooler star.

Problem 2 (3 points): A photon is observed to have a wavelength of 21 cm. What is the frequency of this photon? What is the energy of this photon? In what part of the electromagnetic spectrum does this photon lie?

Problem 3: (6 points) The infrared flux from an asteroid is half the visible flux. The reflected flux measured from this asteroid is 3.3x10-16 watts/m2. The asteroid is at opposition meaning that it is exactly opposite the Sun in the sky. Its distance from the Sun is 2.7 AU and being at opposition, it is 1.7 AU from Earth. Using the fact that LSun=3.9x1026 watts, compute the diameter of this asteroid.

Problem 4: (6 points) Compare the average velocities of oxygen and hydrogen molecules on the surfaces of the Earth, Moon and Mercury with the escape velocities from these bodies. To facilitate the comparison, plot the Maxwell-Boltzmann distribution for hydrogen on each of these objects and indicate the most probable velocity on the plot. For computational purposes, assume that 1000 hydrogen molecules are being described by the Maxwell-Boltzmann distribution. Assume that the surface temperature of the Earth is 290K, the Moon is 300K, and Mercury is 550K.

Problem 5 (5 points): A rock sample contains 40Ar and 40K in the ratio of 40Ar/40K = 3. How old is the rock? What assumptions do you have to make to calculate an age? The half life for the decay of 40K to 40Ar is 1.3x109 years.