Suppose we observe the Ho line from a spherical planetary nebula, and find it has a maximum wavelength of 656.32 nm and minimum wavelength of 656.24. a. Estimate how fast the nebula is expanding? Give your answer in both km/s and au/year. b. Now suppose that over a time of 10 years the nebula's angular diameter is observed to expand from 10 arcsec to 10.1 arcsec. What is the distance to the nebula, in pc? c. What is actual physical diameter of the nebula, in au?