Assignment:
Part 1:
1. Star X has a surface temperature 2 times higher than the Sun and a radius 0.01 times that of the Sun.
Star Y is 50 times farther away from the Earth than is star X; it has a surface temperature 4 times hotter than the Sun and a radius√2 times that of the Sun. Which star is brighter as observed from the Earth and by how many times brighter is it than the other star? (That is, what is the ratio of its brightness to that of the fainter star?)
2. A star has a "surface" temperature of 10,000 K.
a. Calculate the peak wavelength of its brightness vs. wavelength curve.
b. What color does this wavelength correspond to? (Note: if the wavelength is in the infrared or ultraviolet range, state "IR" or "UV" as the color.)
c. Now imagine that the star is moving away from us at 0.2c, where c is the speed of light. What peak wavelength would we observe in this case?
d. What color does the peak wavelength obtained in part (c) correspond to? (See note in part b.)
Part 2:
1. Astronomers observe two stars, A and B.
a. Star A has a parallax of 0.02 arcseconds. Calculate the distance to star A.
b. Star B has a spectrum that is identical to that of star A, indicating that the two are the same type of star with the same luminosity. However, the brightness of star B as observed from the Earth is only 0.0025 times that of star A. Calculate the distance to star B.
2. Star J, a Cepheid variable star observed in a cluster of stars in the Milky Way lying at a distance of 5.0 kpc (= 0.0050 Mpc) from the Earth, has a brightness that changes in cycles with a period of 3.0 days. Star K, a Cepheid variable in another galaxy, has a period of 60 days and a brightness that is 1.0x10-7 times that of star J. What is the distance in Mpc to the galaxy containing star K?
3. A very luminous type of star is observed in galaxy X, and another star of identical type is observed in galaxy Y. The distance to galaxy X has already been determined to be 5.0 Mpc. The star in galaxy X is 10,000 times brighter than the star in galaxy Y. Calculate the distance to galaxy Y.