91Ó°ÊÓ

The average density of interstellar gas within the Local Bubble is much lower than the value mentioned in the text \(-\) in fact, it is roughly \(10^{3}\) hydrogen atoms \(/ \mathrm{m}^{3}\). Given that the mass of a hydrogen atom is \(1.7 \times 1^{-27} \mathrm{kg}\), calculate the total mass of interstellar matter contained within a bubble volume equal in size to planet Earth.

Interstellar extinction is sometimes measured in magnitudes per kiloparsec \((1 \mathrm{kpc}=1000 \mathrm{pc})\). Light from a star \(1500 \mathrm{pc}\) away is observed to be diminished in intensity by a factor of 20 over and above the effect of the inverse-square law. What is the average interstellar extinction, in \(\mathrm{mag} / \mathrm{kpc}\) along the line of sight?

A beam of light shining through a dense molecular cloud is diminished in intensity by a factor of 2 for every \(5 \mathrm{pc}\) it travels. By how many magnitudes is the light from a background star dimmed if the total thickness of the cloud is 60 pc?

A star of apparent magnitude 10 lies 500 pc from Earth. If interstellar absorption results in an average extinction of \(2 \mathrm{mag} / \mathrm{kpc},\) calculate the star's absolute magnitude and luminosity.

To carry enough energy to ionize a hydrogen atom, a photon must have a wavelength of less than \(9.12 \times 10^{-8} \mathrm{m}\) \((91.2 \mathrm{nm}) .\) Using Wien's law, calculate the temperature a star must have for the peak wavelength of its blackbody curve to equal this value.