Chapter 12, Problem 18SEQ

Explain all answers clearly, with complete sentences and proper essay structure if needed. An asterisk (*) designates a quantitative problem, for which you should show all your work.

Cepheids in M100. Consider these actual data for three Cepheids in the galaxy M100 (measured with observations from the Hubble Space Telescope). The luminosities were determined from the observered periods using Leavitt’s Law.

• Cepheid 1 : $\text{luminosity}=3.9\times {10}^{30}\text{watts}$

$\text{apparent}$ $\text{brightness}=9.3\times {10}^{-19}\text{watt}/{\text{m}}^2$

• Cepheid 2 : $\text{luminosity}=1.2\times {10}^{30}\text{watts}$

$\text{apparent}$ $\text{brightness}=3.8\times {10}^{-19}\text{watt}/{\text{m}}^2$

• Cepheid 3 : $\text{luminosity}=2.5\times {10}^{30}\text{watts}$

$\text{apparent}$ $\text{brightness}=8.7\times {10}^{-19}\text{watt}/{\text{m}}^2$

Compute the distance to M100 with data from each of three Cepheids. Do the three distance computations agree? Based on your results, estimate the uncertainty in the distance you have found.