a) Describe how we measure distance using parallax. What is the practical limitation of this technique, and what is the approximate distance (in parsecs) out to which this technique is useful.
b) Describe how we measure distance using "spectroscopic parallax". What is the practical limitation in using this technique, and what is the approximate distance (in parsecs) out to which this technique is useful.
c) How do we use the spectral class and the apparent color of a star to determine the amount of dust and gas (the "crud") that lies between us and the star.